neural bases of approach and avoidance 1 neural bases of...

Neural Bases of Approach and Avoidance 1

Neural Bases of Approach and Avoidance

Eddie Harmon-Jones

Texas A&M University

Acknowledgements. Work on this article was supported by National Science Foundation grants

BCS 0350435 and BCS 0643348. Correspondence concerning this article should be addressed to

Eddie Harmon-Jones, Department of Psychology, Texas A&M University, 4235 TAMU, College

Station, TX, USA 77845. Email: [email protected]

mailto:[email protected]


Self-enhancement can be viewed as varying along several bipolar dimensions, as noted

by Sedikides and Gregg (2008). One dimension ranges from self-advancing to self-protecting,

and this typically occurs by augmenting the positivity or diminishing the negativity of the self-

concept or self-regard (Arkin, 1981). This dimension of self-enhancement may be a subset of the

more general distinction between approach and avoidance (Alicke & Sedikides, 2009; Elliot &

Mapes, 2005), a fundamental motivational dimension present in most living organisms

(Schneirla, 1959). Approach motivational processes underlie self-enhancement or self-

advancement strivings that guide individuals toward selecting situations in which they are likely

to excel and toward promoting their virtues when fear of contraction is low (Alicke & Sedikides,

2009). Avoidance motivational processes, on the other hand, underlie self-protection strivings

that assist in processes such as retreating from threatening situations, staying away from

situations that threaten failure, and misremembering negative information about the self (Alicke

& Sedikides, 2009).

This chapter provides a review of research on the neural bases of approach and avoidance

motivation, that is, brain regions involved in responses to rewards and punishments. Much of this

research is predicated on models that assume approach motivation and responses to rewards

involve a positive affective system, whereas avoidance motivation and responses to punishments

involve a negative affective system.

The basic motivational dispositions toward approach and withdrawal are often associated

with emotions. However, an emotion is not a ―thing‖ but is a multi-component process made up

of basic processes such as feelings of pleasure or displeasure, facial/body expression

components, particular appraisals, and particular action plans and activation states (Frijda, 1993).

Moreover, these components are not perfectly correlated with each other (Lang, 1995).


Approach and withdrawal motivational processes likely involve brain systems and not

only specific brain structures. However, this systems level analysis has yet to be well

investigated because of the empirical difficulties of mapping these micro-processes in time.

Consequently, I will focus this review on brain regions that have received the most research

attention in motivation. These are the amygdala, nucleus accumbens/ventral striatum, the

orbitofrontal cortex, the anterior cingulate cortex, and asymmetrical frontal cortical regions. The

following review is necessarily incomplete because of the vast amount of research currently

being conducted.

Finally, I should emphasize that it is difficult to make one-to-one associations between

psychological processes and physiological processes. For example, if neurons in the amygdala

become more active, it is almost impossible to claim that this activation reflects a certain

psychological variable like fear. As will be reviewed, amygdala neurons become active in

response to a wide range of psychological variables, including uncertainty (Whalen, 1998),

positive affect (Anderson et al., 2003), and motivational relevance (Cunningham, Van Bavel, &

Johnsen, 2008).

Perception of Motivational Relevance

Many of the stimuli that arouse motivation are perceived with the visual or auditory

system. The processes of orienting and attending have been posited to ―stem from the activation

of defensive and appetitive motivational systems that evolved to protect and sustain the life of

the individual‖ (Bradley, 2009, p. 1). Attention and emotive processes are inextricably linked.

Novel and significant events attract our attention. Novel and significant or relevant events

evoke an orienting or ―what is it‖ response. Of course, defining ―significance‖ can be difficult,

but several researchers have suggested that significance can be defined in terms of approach and


avoidance behavior (Thorndike, 1911) or in terms of the pleasure and arousal or emotion evoked

(Bradley, 2009; Maltzman, 1979). Emotion is often theorized to fundamentally be a disposition

to act, to behave effectively to events that threaten or promote life (Frijda, 1986; Lang, 1985).

These motivational tendencies are realized in general systems of approach and avoidance, with

approach processes often acting to promote survival and avoidance processes often acting to

prevent threats to well-being. Some theorize that judgments of positivity reflect approach

motivation, judgments of negativity reflect avoidance motivation, and judgments of arousal

index the intensity of activation or motivation (Bradley, 2009). Although this may often be the

case, the relationship between emotional valence and motivational direction (i.e., approach

motivation is positive) is not always that direct. For instance, anger, a negatively valenced

emotion, is often associated with approach motivation (Carver & Harmon-Jones, 2009), a point

to which we return later.

Emotional stimuli automatically capture attention (Ohman, Flykt, & Esteves, 2001). The

neural specifics of this process have been examined most extensively using auditory conditioned

stimuli (single tones) that evoke fear in rats. The conditioned stimulus is transmitted through the

auditory system to the auditory thalamus, including regions of the medial geniculate body and

regions of the posterior thalamus (LeDoux, Farb, & Ruggiero, 1990). Then, signals are sent from

all regions of the auditory thalamus to the auditory cortex, while a subset of thalamic nuclei send

signals to the amygdala. This thalamo-amygdala pathway begins in the medial division of the

medial geniculate body and associated posterior intralaminar nucleus (LeDoux, Cicchetti,

Xagoraris, & Romanksi, 1990). Signals from the auditory cortex also project to the amygdala

(Mascagni, McDonald, & Coleman, 1993). These two pathways to the amygdala, the thalamo-

amygdala and thalamo-cortico-amygdala pathways, terminate in the sensory input region of the


amygdala, the lateral nucleus (LeDoux et al., 1990; Mascagni et al., 1993). These two pathways

are often referred to as the low road (thalamo-amygdala) and high road (thalamo-cortico-

amygdala) to the amygdala. However, the high road is not necessary for the acquisition of

conditioned fear (Romanski & LeDoux, 1992). But the high road is likely more involved in

processing of more complex stimuli (LeDoux, 1996).

Once sensory information enters the lateral nucleus of the amygdala, it is then transmitted

via intra-amygdala connections to the basal and accessory basal nuclei (Pitkänen, Savender, &

LeDoux, 1997). There, it is integrated with other incoming information from other areas and then

transmitted to the central nucleus of the amygdala. The central amygdala is the main output

system of the amygdala and it projects to structures that affect blood pressure, freezing behavior,

and hormone release (LeDoux, 1996).

Research with primates has demonstrated extensive neuroanatomical connectivity

between the amygdala and the visual cortex (Amaral, Price, Pitkanen, & Carmichael, 1992;

Freese & Amaral, 2005). In humans, amygdala responses predict neural activity in areas of the

visual cortex in response to emotional images (Morris et al., 1998; Sabatinelli, Bradley,

Fitzsimmons, & Lang, 2005). In addition, damage to the amygdala has been associated with

decreased activity in the visual cortex to emotional stimuli. Research with humans measuring

event-related brain potentials (ERPs) recorded over the parietal region has revealed that pictorial

emotional stimuli show differences from neutral stimuli as early as 136 ms following stimulus

onset (Foti, Hajcak, & Dien, 2009), and it has been suggested that this early ERP reflects

selective attention.

Amygdala


As illustrated above, one of the most investigated structures in emotive research is the

amygdala. It is well-known for its involvement in fear, although more recent research has

revealed the story to be more complex than that, as will be reviewed below. The amygdala,

which is composed of approximately a dozen nuclei (Pikänen et al., 1997), is critically involved

in learning, storage, and expression of emotive processes. The amygdala is an almond-shaped

structure on the medial temporal lobe, sitting slightly in front of the hippocampus. The

importance of the amygdala in emotive processes was first recognized by Kluver and Bucy

(1937) who demonstrated that lesioning the medial temporal lobe of monkeys caused the

monkeys to approach normally feared objects and exhibit unusual sexual behaviors. Weiskrantz

(1956) later demonstrated that it was lesioning the amygdala within the medial temporal lobe that

caused these behaviors.

Three amygdala nuclei have been identified as important in fear – the lateral nucleus,

central nucleus, and basal nucleus. The lateral nucleus receives input from thalamic and cortical

regions, and the lateral nucleus connects to the central nucleus both directly and indirectly via

projections to the basal nucleus. The lateral nucleus is involved in the acquisition and storage of

fear conditioning, whereas the basal nucleus and central nucleus are involved in the expression

of fear (Cain & LeDoux, 2008).

Animal research has also revealed that the amygdala is involved in positive emotional

reactions. For example, in rats, amygdala lesions cause a failure to work for a salty reward even

when rats are in a physiological state of sodium depletion (Schulkin, 1991). Moreover, amygdala

lesions cause rats to fail to consume salt that is freely given to them, even though they display

positive reactions to a salty taste if it is placed in their mouths (Schulkin, 1991). Other research

has suggested that amygdala damage causes a disruption of reward learning (Everitt & Robbins,


1992). Male rats fail to perform a learned task to gain access to sex after amygdala damage, even

though the same rats will engage in sex if access to the female is freely granted (Everitt, 1990).

The animal research has revealed that destruction of the amygdala is clearly not sufficient

to eliminate all emotional learning, because many aspects of learned reward and learned fear

exist after amygdala removal. For instance, monkeys still show fear to extremely strong stimuli

after bilateral amygdala destruction (Kling & Brothers, 1992). Along these lines, some studies

have revealed that humans with bilateral amygdala damage still show normal recognition of

vocal expressions of fear (Anderson & Phelps, 1998), and individuals with amygdala damage

show normal patterns of daily mood (Anderson & Phelps, 2002). Taken together, this work

reveals that although the amygdala may be involved in emotional processes, it is not necessary

for the production of these states.

Human research has largely confirmed the animal results, although with less spatial

precision. Currently, the best technique for measuring amygdala activation in humans is

functional magnetic resonance imaging (fMRI). The spatial resolution for a 3 Tesla magnet is on

the order of a 3 mm cube or voxel, but such a voxel contains hundreds if not thousands of

neurons. Moreover, fMRI relies on blood flow, blood volume, and blood oxygenation to detect

neuronal activation, and regions that contain neurons too closely packed together, such as the

hypothalamus or amygdala, do not permit detailed measurements of subpopulations of neurons

within the regions.

Human neuroimaging research has converged with the animal research to reveal that the

amygdala is important in fear processing. For instance, the amygdala region is more activated by

a neutral stimulus paired with an aversive event (conditioned stimulus) compared to another

neutral stimulus that does not predict an aversive event (LaBar et al., 1998). Moreover, amygdala


activation correlates with the conditioned response of increased skin conductance (an indication

of arousal) to the conditioned stimulus (LaBar et al., 1998). Going beyond these correlations

between amygdala activations and responses to stimuli, research has revealed that patients with

lesions including the right, left, or bilateral amygdala do not demonstrate a conditioned response

as measured by skin conductance even though they respond normally to the unconditioned

(aversive) stimulus (Bechara et al., 1995). These results fit well with the animal research

demonstrating that the amygdala plays an important role in fear conditioning.

Interestingly, although the amygdala is important for the acquisition of fear as measured

by skin conductance, a measure of implicit learning, it does not appear to be important for the

acquisition of fear learning measured explicitly. Individuals who suffer bilateral amygdala

damage acquire explicit knowledge about the relationship between the conditioned stimulus and

the aversive unconditioned stimulus (Gazzaniga et al., 2002). This type of explicit knowledge is

due to the hippocampus (Squire & Zola-Morgan, 1991). Individuals who have a damaged

hippocampus but intact amygdala show normal skin conductance response to conditioned stimuli

but no explicit knowledge of the relationship between the conditioned stimulus and

unconditioned stimulus (Bechara et al., 1995).

More recent human neuroimaging research has revealed that the amygdala becomes

activated in response to a variety of emotive stimuli in addition to fear-provoking ones. For

instance, experiments have revealed that positive stimuli also evoke greater amygdala activity

than neutral stimuli (Breiter et al., 1996). Other studies have independently manipulated valence

and intensity and found that amygdala activity is more associated with processing affective

intensity than with processing any specific valence (Anderson et al., 2003). Consistent with


results obtained from these studies, several researchers have suggested that the amygdala is

generally vigilant for motivationally relevant stimuli (Anderson & Phelps, 2001; Whalen, 1998).

In an excellent illustration of this point, Cunningham, Van Bavel, and Johnsen (2008) had

participants provide bivalent (positive to negative) ratings of famous people, positive ratings

(from none to very good) of famous people, or negative ratings (from none to very bad) of

famous people. When participants provided bivalent evaluations, both positive and negative

names were associated with amygdala activation. When they provided positive evaluations,

positive names were associated with amygdala activity, and when they provided negative

evaluations, negative names were associated with amygdala activity. In addition, a negativity

bias was found, such that amygdala activity was more modulated for positive than for negative

information. These results suggest that the amygdala flexibly processes motivationally relevant

evaluative information in accordance with current processing goals, but processes negative

information less flexibly than positive information.

Other brain regions contributed to this affective flexibility observed in the amygdala.

This occurred only in the negative-only and positive-only conditions where participants had to

selectively process a subset of information to determine affective connotations, because such

requires deliberate processing. Cunningham et al. (2008) found that right dorsolateral prefrontal

cortex was more active in the positive and negative conditions than in the bivalent condition, and

that several areas were more associated with amygdala activation in the positive and negative

conditions than in the bivalent condition. These areas were medial areas of orbitofrontal cortex,

right lateral orbitofrontal cortex, right rostrolateral prefrontal cortex, left orbitofrontal cortex, and

anterior cingulate. Taken together, these results suggest that the amygdala is responsive to


motivational relevance and that areas of the prefrontal cortex play a role in amygdala activation

particularly when individuals deliberately process motivational information.

Nucleus Accumbens/Ventral Striatum

Other brain regions critically important for emotive processes are the nucleus accumbens

and ventral striatum. The nucleus accumbens lies at the front of the sub-cortical forebrain. It is

rich in dopamine and opioid neurotransmitters, and it is famous for being involved in positive

affect or feeling good. However, like the amygdala, research has revealed the story of the

nucleus accumbens to be more complex than only one of positive affect.

Dopamine cell bodies in the ventral tegmental area have projections to forebrain regions

including the nucleus accumbens, amygdala, ventral pallidum, and prefrontal cortex. These

regions also project back both directly and indirectly to the ventral tegmental area. A number of

theories have developed to explain the psychobehavioral functions of this mesocorticolimbic

dopamine system. Incentive salience theory posits that the mesolimbic dopamine system

provides the motivation to direct behavior toward reward-related stimuli (Berridge, 2000, 2007).

Increased dopamine function in these regions is critical to the ―wanting‖ of stimuli and not

critical for pleasure, hedonic impact, of the ―liking‖ of rewarding stimuli. Consistent with this

hypothesis, research has found that drug craving but not drug pleasure to a pleasurable drug

(amphetamine or cocaine) was reduced when suppression of dopamine neurotransmission in

humans was manipulated (Brauer & DeWit, 1997). Similarly, human functional neuroimaging

research has revealed that the nucleus accumbens is activated during pre-goal positive emotion

but not during post-goal positive emotion. In contrast, the medial prefrontal cortex is activated

during post-goal positive emotion but not during pre-goal positive emotion (Knutson &

Wimmer, 2007).


In humans, functional magnetic resonance imaging research has revealed that the nucleus

accumbens becomes active during the anticipation of rewards. For instance, Knutson, Wimmer,

Kuhnen, and Winkielman (2008) found that anticipation of viewing rewarding stimuli (erotic

pictures for heterosexual men) increased nucleus accumbens activity and financial risk taking.

Nucleus accumbens activity also increased in anticipation of making a risky decision, that is, a

high ($1.00) as compared to a low ($0.10) risk financial gamble. Moreover, the risk taking was

partially mediated by increases in nucleus accumbens activation.

However, dopamine and the nucleus accumbens have been revealed to be involved in

more than only wanting. Specific subregions of the nucleus accumbens in combination with

specific neurotransmitters may be involved in ―liking‖ or post-goal positive affect. For instance,

microinjection of morphine, which activates opioid receptors, into posterior and medial regions

of the accumbens shell increases positive affective reactions to sweet tastes (Peciña & Berridge,

2000). Other research has revealed that the nucleus accumbens is critical in regulating effort-

related functions (Salamone, 2007), such that lever pressing schedules that require minimal work

are unaffected by accumbens dopamine depletions, whereas lever-pressing schedules that require

high work are impaired by accumbens dopamine depletions (Salamone, 2007).

Other research has revealed that dopamine accumbens systems are activated in aversive

situations such as expecting or receiving footshock or other stressors (Gray et al., 1997;

Salamone, 1994). More recent research has examined both appetitive and aversive behaviors and

tested whether sub-regions of the nucleus accumbens are responsible for these different emotive

reactions (Reynolds & Berridge, 2001, 2002). Injections of GABA agonists into the rostral

(front) shell of the nucleus accumbens, which should increase GABAergic neural transmission,

increased appetitive behaviors (e.g., eating, place preference, orofacial expressions of taste-


elicited liking). In contrast, injections of the same substance into the caudal (back) shell of the

nucleus accumbens increased fearful defensive behaviors (e.g., place avoidance, orofacial

expressions of taste-elicited disliking). Human neuroimaging research has replicated this rostral-

caudal distinction in the nucleus accumbens (Seymour, Daw, Dayan, Singer, & Dolan, 2007).

Other work has suggested that dopamine and acetylcholine have opposing roles in the nucleus

accumbens, with dopamine fostering approach and acetylcholine fostering inhibition or

avoidance (Hoebel, Avena, & Rada, 2007).

In a fascinating extension of this research, Reynolds and Berridge (2008) found that

exposing rats to stressful environments caused the caudal fear-generating zones to expand

rostrally, filling approximately 90% of the nucleus accumbens shell. In contrast, a preferred

home environment caused fear-generating zones to shrink and appetitive-generating zones to

expand caudally, filling approximately 90% of the shell. This work illustrates that emotional

environments can modify the generation of motivation in specific brain circuits. It also illustrates

the plasticity of brain regions involved in motivation.

Orbitofrontal Cortex

The bottom (ventral) one-third of the pre-frontal cortex is called the orbitofrontal cortex.

It is most developed in humans and primates but it is present to some extent in all mammals. The

orbitofrontal cortex receives inputs from sensory modalities including gustatory, olfactory,

somatosensory, auditory, and visual. It also receives visceral sensory information. This large

amount of input makes the orbitofrontal cortex one of the most polymodel regions in the cortex

(Kringelbach, 2005). The orbitofrontal cortex has direct reciprocal connections with a number of

other brain structures, including the amygdala, cingulate cortex, insula/operculum,


hypothalamus, hippocampus, striatum, periqueductal grey, and dorsolateral prefrontal cortex

(Kringelbach & Rolls, 2004).

Neurons in this region fire when monkeys taste desired foods and even when the

monkeys only see the food or an associated stimulus (Rolls, 1997, 2000; Rolls, Yaxley, &

Sienkiewicz, 1990). These neurons respond to affective, rewarding qualities of the stimulus and

not simply the sensory quality of the taste. For example, neurons stop firing once the monkey has

eaten its fill of the desirable food (Rolls et al., 1988). In rats, orbitofrontal cortex neurons fire

action potentials in response to cocaine or heroin (Chang, Janak, & Woodward, 1998), and rats

will work to obtain a microinjection of cocaine or related drugs into the medial prefrontal region

(Carlezon & Wise, 1996). Animal research has also revealed that orbitofrontal cortex is activated

to negative affective stimuli (Berridge, 2003).

Human neuroimaging studies have also found increased activity in the orbitofrontal

cortex in response to pleasant and unpleasant stimuli. Using functional magnetic resonance

imaging (fMRI) and many affective stimuli (e.g., faces, odors, gambles, tastes), research has

found that different subregions of the orbitofrontal cortex are involved in reward and punishment

processing. Monetary reward and pleasant odors, smells, and faces activate the medial

orbitofrontal cortex. In contrast, monetary punishment and unpleasant odors, smells, and faces

activate the lateral orbitofrontal cortex (O’Doherty, Winston, Critchley, Perrett, Burt & Dolan,

2003; Gottfried, O’Doherty & Dolan, 2002; O’Doherty, Kringelbach, Rolls, Hornak & Andrews,

2001; O’Doherty, Deichmann, Critchley & Dolan, 2002). In addition to this mediolateral

distinction, a posterior–anterior distinction exists within the orbitofrontal cortex: more complex

or abstract reinforcers (such as monetary gain and loss) involve more anterior regions, whereas


more simple reinforcers involve more posterior regions (see Kringelbach & Rolls, 2004, for

review).

However, the complete loss of affective reactions due to orbitofrontal cortex damage is

extremely rare (Damasio, 1994, 1996). Individuals with lesions to this region still seek some

simple pleasures (e.g., they choose palatable foods and eat them), and they react to pains and

avoid unpleasant events. Similar effects have been observed in animals (Berridge, 2003). These

results suggest that the orbitofrontal cortex is not the chief site for the representation of primary

reinforcers and that it may be involved in other aspects of emotional processing (Berridge, 2003),

as noted below.

Another body of research has emphasized the importance of the orbitofrontal cortex for

reversal learning (Schoenbaum, Setlow, & Ramus, 2003) or self-monitoring (Prigatano, 1991;

Stuss, 1991; Stuss & Benson, 1984). In reversal learning, an animal is taught that responding to

one cue produces reward, whereas acting similarly to another cue produces nonreward or

punishment. After the animal learns to respond correctly, the experimenter switches the cue–

outcome associations, and the animal must learn to change its behavior. During cue-outcome

learning across reversals, the orbitofrontal cortex is activated (O’Doherty, Critchley, Deichmann,

& Dolan, 2003). However, orbitofrontal lesions do not affect reversal of some innate response

tendencies (Chudasama, Kralik, & Murray, 2007). In the literature on the orbitofrontal cortex,

self-monitoring is defined as the ability to evaluate one’s behavior in the moment in reference to

higher order goals or the reactions of other people (Beer, John, Scabini, & Knight, 2006). This is

the process ―by which individuals evaluate their behavior in the moment to make sure that the

behavior is consistent with how they want to behave and how other people expect them to

behave‖ (Beer et al., 2006, p 872). Individuals with orbitofrontal cortex damage have an


impaired ability to prioritize solutions to interpersonal problems (Saver & Damasio, 1991), a

tendency to greet strangers in an overly familiar manner (Rolls, Hornak, Wade, & McGrath,

1994), and behave in disruptive manners in hospital settings (Blair & Cipolotti, 2000). They also

tease strangers inappropriately and are more likely to include unnecessary personal information

when answering questions (Beer, Heerey, Keltner, Scabini, & Knight, 2003; Kaczmarek, 1984).

This self-monitoring perspective on orbitofrontal cortex is consistent with the previously

reviewed research on the emotional functions of the orbitofrontal cortex when functional

accounts of emotion are considered. That is, self-monitoring may be critical for generating social

emotions that help promote adaptive social behavior (Beer et al., 2006).

Anterior Cingulate Cortex

Sometimes, stimuli may directly cause behavior. In such cases, information may proceed

from sensory processing areas of the brain to structures involved in approach and avoidance. In

other cases, however, information may be more complex or multiple response options exist. In

such cases, brain regions implicated in decision making become active to assist in deciding

whether to approach or avoid. One area that has received research attention on these issues is the

anterior cingulate cortex.

In much of this research, response conflicts are examined on task such as the color-

naming Stroop (1935) task. For example, when completing the color-naming Stroop task, one’s

goal is to identify the ink color of a word stimulus, regardless of the word’s meaning. However,

the processing of word meaning is typically automatic, and when a word’s meaning is

incongruent with one’s goal to judge the word’s color, such as when the word ―red‖ is presented

in blue ink, there is conflict between the intended and the automatic response tendencies. In

studies examining neural activity during the Stroop task, anterior cingulate cortex activity is


greater during incongruent trials than congruent trials (Carter et al., 1998; Gehring, Goss, Coles,

Meyer, & Donchin, 1993). Similar findings have been observed using other response-conflict

tasks, such as the Eriksen and Eriksen’s (1974) flanker’s task and the Go/No-Go task (Botvinick,

Nystrom, Fissel, Carter, & Cohen, 1999; Keihl, Liddle, & Hopfinger, 2001). Researchers have

interpreted these findings as evidence that the anterior cingulate cortex plays an important role in

monitoring the moment-to-moment representations of action tendencies for potential conflicts,

presumably so that other mechanisms may be engaged to override the unwanted tendency and to

promote an effective goal-directed response (Botvinick, Barch, Braver, Cohen, & Carter, 2001).

Thus, conflict monitoring represents the first component of a dual-process model of cognitive

control, whereby the need for control is initially detected.

Amodio et al. (2004) integrated the conflict-monitoring framework with social

psychological theories of self-regulation by examining conflict between automatic stereotyping

tendencies and participants’ goals to respond without prejudice. In this study, anterior cingulate

cortex activity was monitored using an event-related potential measure referred to as the ―error-

related negativity‖ component (Gehring et al., 1993; van Veen & Carter, 2001). When

participants – who reported low-prejudice attitudes– accidentally made responses that reflected

the application of racial stereotypes, thus constituting a clear response conflict, the anterior

cingulate cortex was strongly activated. By comparison, anterior cingulate cortex activity was

lower on other trial types that did not elicit conflicting actions. In subsequent research, Amodio,

Devine, and Harmon-Jones (2008) demonstrated that heightened anterior cingulate cortex

activity associated with racially-biased responses was only observed for participants with strong

personal motivations to respond without prejudice. Furthermore, across studies, participants with

stronger anterior cingulate cortex activity were more likely to engage in controlled behavior


(slower, more careful responding). These results suggest that the anterior cingulate cortex may

be involved in coping with conflicts between various responses such as approach-avoidance

conflicts.

Asymmetric Frontal Cortical Regions

The asymmetric involvement of prefrontal cortical regions in positive affect (or approach

motivation) and negative affect (or withdrawal motivation) was suggested over 70 years ago by

observations of persons who had suffered damage to the right or left anterior cortex (Goldstein,

1939). Later research supported these observations using the Wada test, which involves injecting

amytal, a barbiturate derivative, into one of the internal carotid arteries and suppressing the

activity of one hemisphere. Amytal injections in the left side produced depressed affect, whereas

injections in the right side produced euphoria (Alema, Rosadini, & Rossi, 1961; Perria, Rosadini,

& Rossi, 1961; Rossi & Rosadini, 1967; Terzian & Cecotto, 1959). These effects were

interpreted as reflecting the release of one hemisphere from contralateral inhibitory influences.

Thus, activation in the right hemisphere, when not inhibited by the left hemisphere, caused

depression; an uninhibited left hemisphere caused euphoria.

Subsequent studies appeared to confirm these results, finding that persons who had

suffered left hemisphere damage or lesions tended to show depressive symptoms (Black, 1975;

Gasparrini, Satz, Heilman, & Coolidge, 1978; Gainotti, 1972; Robinson & Price, 1982), whereas

persons who had suffered right hemisphere lesions tended to show manic symptoms (Gainotti,

1972; Robinson & Price, 1982; Sackeim et al., 1982). Other research has revealed asymmetries

underlying appetitive and avoidant behaviors in non-human animals, in species ranging from

great apes and reptiles (Deckel, Lillaney, Ronan, & Summers, 1998; Hopkins, Bennett, Bales,

Lee, &Ward, 1993) to chicks (Güntürkün et al., 2000), amphibians (Rogers, 2002), and spiders


(Ades & Ramires, 2002).

More recent research suggests that in humans these asymmetric activations are often

specific to the frontal cortex. This research often uses asymmetric activation in right versus left

frontal cortical areas as a dependent variable, usually assessed by electroencephalographic (EEG)

recordings. Frontal cortical asymmetry is assessed by comparing activation levels between

comparable areas on the left and right sides. Difference scores are widely used in this research,

and their use is consistent with the amytal and lesion research described above that suggests that

asymmetry may be the key variable with one hemisphere inhibiting the opposite one. Consistent

with that view is evidence from studies of transcranial magnetic stimulation, discussed later

(Schutter, 2009; Schutter, van Honk, d’Alfonso, Postma, & de Haan, 2001).

Much of this evidence has been obtained with EEG measures of brain activity, or more

specifically, alpha frequency band activity derived from the EEG. Research has revealed that

alpha power is inversely related to regional brain activity using hemodynamic measures (Cook,

O’Hara, Uijtdehaage, Mandelkern, & Leuchter, 1998) and behavioral tasks (Davidson, Chapman,

Chapman, & Henriques, 1990). Source localization of EEG signals (Pizzagalli, Sherwood,

Henriques, & Davidson, 2005) and fMRI results obtained in emotion-frontal asymmetry studies

converge in suggesting that the dorsolateral prefrontal cortex is responsible for these effects

(Berkman & Lieberman, in press).

Trait Affective Styles and Resting Asymmetric Frontal Activity

Depression has been found to relate to resting frontal asymmetric activity, with depressed

individuals showing relatively less left than right frontal brain activity (Jacobs & Snyder, 1996;

Schaffer, Davidson, & Saron, 1983), even when in remission status (Henriques & Davidson,

1990). Other research has revealed that trait positive affect is associated with greater left than


right frontal cortical activity, whereas trait negative affect is associated with greater right than

left frontal activity (Tomarken, Davidson, Wheeler, & Doss, 1992).

Subsequent studies observed that trait approach motivation was related to greater left than

right frontal activity at resting baseline (Amodio, Master, Yee, & Taylor, 2008; Harmon-Jones &

Allen, 1997; Sutton & Davidson, 1997). These studies suggested that asymmetric frontal cortical

activity could be associated with motivational direction instead of affective valence. However,

avoidance and approach motivation are mostly associated with negative and positive affect,

respectively (Carver & White, 1994), and consequently, the interpretation is clouded. Similarly,

the finding of promotion (versus prevention) focus being associated with greater relative left

(versus right) frontal activation at baseline (Amodio, Shah, Sigelman, Brazy, & Harmon-Jones,

2004) could be interpreted from a motivational direction view or an affective valence view

because promotion (versus prevention) is more often associated with positive (versus negative)

affect. That is, past research had essentially confounded emotional valence with motivational

direction, but researchers had made the interpretation that relatively greater left than right frontal

cortical activity reflected greater approach motivation and positive affect, whereas relatively

greater right than left frontal cortical activity reflected greater withdrawal motivation and

negative affect. These claims fit well into dominant emotion theories that associated positive

affect with approach motivation and negative affect with withdrawal motivation (Lang, 1995;

Watson, 2000).

However, other theories suggested that approach motivation and positive affect are not

always associated with one another. Anger, for example, is a negatively valenced emotion that

evokes behavioral tendencies of approach (e.g., Darwin, 1872; Ekman & Friesen, 1975; Plutchik,

1980; Young, 1943). Anger is associated with attack, particularly offensive aggression (e.g.,


Berkowitz, 1993; Blanchard & Blanchard, 1984; Lagerspetz, 1969). And offensive aggression

can be distinguished from defensive aggression, which is associated with fear. Offensive

aggression leads to attack without attempts to escape, whereas defensive or fear-based

aggression leads to attack only if escape is not possible. Other research also suggested that anger

was associated with approach motivation (e.g., Izard, 1991; Lewis, Alessandri, & Sullivan, 1990;

Lewis, Sullivan, Ramsay, & Alessandri, 1992). More recent studies examined whether trait

behavioral approach or BAS related to anger-related responses. Several studies have found that

trait behavioral approach sensitivity (BAS), as assessed by Carver and White’s (1994) scale, is

positively related to state and trait anger (Carver, 2004; Harmon-Jones, 2003; Smits & Kuppens,

2005). Because of the large body of evidence suggesting that anger is often associated with

approach motivation (see Carver & Harmon-Jones, 2009, for a review), research has been

conducted to examine the relationship between anger and relative left frontal activation to test

whether asymmetric frontal cortical activity is due to emotional valence, motivational direction,

or a combination of emotional valence and motivational direction.

Trait anger. Because anger is associated with approach motivation, assessing the

relationship of anger and asymmetric frontal cortical activity can assist in determining whether

asymmetric frontal cortical activity relates to motivational direction or affective valence. If

asymmetric frontal cortical activity relates to motivational direction, then anger should relate to

greater left than right frontal activity, because anger is associated with approach motivational

direction. However, if asymmetric frontal cortical activity relates to affective valence, then anger

should relate to greater right than left frontal activity, because anger is associated with negative

valence.


In a study testing these competing predictions, Harmon-Jones and Allen (1998) assessed

trait anger using the Buss and Perry (1992) questionnaire and assessed asymmetric frontal

activity by examining baseline, resting EEG activity. In this study of adolescents, trait anger

related to increased left frontal activity and decreased right frontal activity. Asymmetric activity

in other regions did not relate with anger. The specificity of anger to frontal asymmetries and not

other region asymmetries has been observed in all of the reviewed studies on anger. These results

have been replicated in a study that revealed that these results were not due to anger being

evaluated as a positive feeling (Harmon-Jones, 2004), and in other studies (Hewig, Hagemann,

Seifert, Naumann, & Bartussek, 2004; Rybak, Crayton, Young, Herba, & Konopka, 2006).

Manipulations of Asymmetric Frontal Cortical Activity and Emotion

Neurofeedback. To test whether these individual differences in asymmetric frontal

cortical activity were causally involved in the production of the affective response, research has

used neurofeedback training to manipulate asymmetric frontal cortical activity (Allen, Harmon-

Jones, & Cavender, 2001). Neurofeedback presents the participant with real-time feedback on

brainwave activity. If brainwave activity over a particular cortical region changes in the direction

desired by the experiment, then the participant is given ―reward‖ feedback; if brainwave activity

does not change in the desired direction, either negative feedback or no feedback is given.

Rewards can be as simple as the presentation of a tone that informs the participant that brain

activity has changed in the desired way. Neurofeedback-induced changes result from operant

conditioning, and these changes in EEG can occur without awareness of how the brain activity

changes occurred (Kamiya, 1979; Siniatchkin, Kropp, & Gerber, 2000). Participants typically are

not aware of how they brought about changes in brain activity; in fact, extensive practice is


required to gain awareness of how one may intentionally cause changes in brain activity (e.g., 8

weeks of practice, Kotchoubey, Kübler, Strehl, Flor, & Birbaumer, 2002).

In the experiment by Allen et al. (2001), individuals were exposed to neurofeedback

training designed to increase relative right versus relative left frontal activity over several days.

Then, on the last day following training, participants were exposed to film clips designed to

evoke emotions, and zygomatic (cheek) and corrugator (brow) muscle region activity was

recorded, to measure positive and negative emotional reactions, respectively. As expected,

neurofeedback training altered asymmetric frontal activity, with individuals who received

neurofeedback training to increase relative right frontal activity showing a significant change in

relative right frontal activity from day 1 to day 3 and 4. Individuals who received training to

increase relative left frontal activity did not show a significant change in asymmetric frontal

activity, but did differ from the relative right frontal training condition on the latter days. More

importantly, this manipulated change in asymmetric frontal cortical activity caused changes in

emotional responses, with the increase in right frontal cortical activity condition showing less

zygomatic and more corrugator muscle region activity in response to all film clips than the

increase left frontal cortical activity condition. This research suggests that asymmetric frontal

cortical activity is causally involved in emotional responses.

Hand contractions. Other research has suggested that asymmetric frontal cortical activity

is causally involved in emotional experience. Contractions of the left hand and of the left side of

the lower third of the face induce sadness and bias perceptions and judgments negatively,

whereas contractions of the right hand and of the right side of the face induce positive affect and

assertiveness and bias perceptions and judgments positively (Schiff & Lamon, 1989, 1994).


The effects of contractions of muscles on one side of the body affecting emotional and

motivational outcomes have been explained as a result of activation of the contralateral

hemisphere. Innervation of facial muscles in the lower third of the face (Rinn, 1984) and of

muscles in the hand is contralateral (Hellige, 1993). Thus, it has been assumed that the emotive

outcomes produced by the contractions resulted from the spread of activation to, or recruitment

of, contralateral frontal areas (Schiff & Lamon, 1989, 1994).

To test these ideas, an experiment was conducted in which participants were randomly

assigned to contract their left or right hand by squeezing a ball for roughly four minutes

(Harmon-Jones, 2006). Then, participants were exposed to a mildly positive, approach-oriented

radio editorial about apartment living options in the city where the participants lived. EEG was

recorded followed by completion of an emotion scale that included items designed to measure

positive activation. Results revealed that the unilateral contraction of the hand increased the

activation of the contralateral hemisphere, as measured by EEG alpha suppression, over the

central and frontal regions. The hand contraction manipulation also affected positive activation,

with the right-hand contraction causing greater positive activation than the left-hand contraction.

Finally, in the right-hand condition, positive activation related to greater relative left frontal

activity at mid-frontal sites, but not other sites.

Repetitive transcranial magnetic stimulation. Other research has manipulated

asymmetrical frontal cortical activity and examined how it affected anger-related responses. For

example, d’Alfonso et al., (2000) used slow repetitive transcranial magnetic stimulation (rTMS)

to inhibit the left or right prefrontal cortex. Slow rTMS produces inhibition of cortical

excitability, so that rTMS applied to the right prefrontal cortex decreases its activation and

causes the left prefrontal cortex to become more active, while rTMS applied to the left prefrontal


cortex causes activation of the right prefrontal cortex. They found that rTMS applied to the right

prefrontal cortex caused selective attention towards angry faces, whereas rTMS applied to the

left prefrontal cortex caused selective attention away from angry faces. Thus, an increase in left

prefrontal activity led participants to attentionally approach angry faces, as in an aggressive

confrontation. In contrast, an increase in right prefrontal activity led participants to attentionally

avoid angry faces, as in a fear-based avoidance. Conceptually similar results have been found by

van Honk and Schutter (2006). The interpretation of these results concurs with other research

demonstrating that attention toward angry faces is associated with high levels of self-reported

anger and that attention away from angry faces is associated with high levels of social anxiety

(van Honk, Tuiten, de Haan, van den Hout, & Stam, 2001).

We recently extended the work of van Honk, Schutter, and colleagues by examining

whether a manipulation of asymmetric frontal cortical activity would affect behavioral

aggression. Based on past research showing that contraction of the left hand increases right

frontal cortical activity and that contraction of the right hand increases left frontal cortical

activity (Harmon-Jones, 2006), we manipulated asymmetric frontal cortical activity by having

participants contract their right or left hand. Participants then received insulting feedback

ostensibly from another participant. They then played a reaction time game on the computer

against the other ostensible participant; the game was designed so that participants would lose on

half of the trials and they could choose how much aversive noise to administer to their opponent,

so that aggression could be unobtrusively measured. Results indicated that participants who

squeezed with their right hand gave significantly louder and longer noise blasts to the other

ostensible participant than those who squeezed with their left hand (Peterson, Shackman, &


Harmon-Jones, 2008). Also, within the right-hand contraction condition, greater relative left

frontal activation was correlated with more aggression.

State Manipulations of Affect and Asymmetric Frontal Cortical Responses

Research has also demonstrated that asymmetric frontal brain activity is associated with

state emotional responses. For instance, Davidson and Fox (1982) found that 10-month-old

infants exhibited increased left frontal activation in response to a film clip of an actress

generating a happy facial expression as compared to a sad facial expression. Frontal brain

activity has been found to relate to facial expressions of positive and negative emotions, as well.

For example, Ekman and Davidson (1993) found increased left frontal activation during

voluntary facial expressions of smiles of enjoyment. Coan, Allen, and Harmon-Jones (2001)

found that voluntary facial expressions of fear produced relatively less left frontal activity.

Other studies have examined emotional processes and frontal asymmetry using event-

related potentials (ERPs). In one study, Cunningham, Espinet, DeYoung, and Zelazo (2005)

measured the late positive potential (LPP) while participants made evaluative (good versus bad)

and non-evaluative (abstract versus concrete) judgments about socially relevant concepts. The

concepts were then rated for goodness and badness. Concepts rated bad caused greater LPPs over

the right frontal hemisphere, while concepts rated good caused greater LPPs over the left frontal

hemisphere. Similarly, van de Laar, Licht, Franken, and Hendriks (2004) found that cocaine-

addicted individuals, but not non-addicted individuals, showed larger positive slow wave

responses over the left (but not right) frontal cortex to cocaine-related photographs as compared

to neutral photographs. Ohgami et al. (2006) also found ERP evidence that suggested that reward

cues caused greater left frontal cortical activity.


The separation of emotional valence from motivational direction suggests that positive

affects vary in motivational intensity. That is, some positive affects are lower in approach

motivation, whereas others are higher in approach motivation. An important question remains

regarding the valence versus motivational direction models of asymmetric frontal cortical

activity: Do positive affects of any approach motivational intensity cause increases in relative

left frontal activation? An experiment addressed this question by assigning participants to write a

short essay on one of three topics (Harmon-Jones, Harmon-Jones, Fearn, Sigelman, & Johnson,

2008). In the neutral mindset condition, participants wrote about an ordinary and neutral day in

their life. In the high-approach-positive mindset condition, participants wrote about a goal that

they intend to accomplish within the next 3 months. In the low-approach-positive mindset

condition, participants wrote about a time when something exceptionally positive happened to

them that did not result from something they did (e.g., when someone did something wonderful

for them). After writing about the event, participants were instructed to think about the event

while EEG was recorded. Consistent with predictions, participants in the two positive mindset

conditions reported feeling more positive affect than participants in the neutral mindset

condition. More importantly, the high-approach-positive mindset condition caused greater

relative left frontal cortical activity than the other conditions. These results support the

hypothesis that it is the approach motivational aspect of some forms of positive affect, and not

the positive valence per se, that causes greater relative left frontal cortical activation (as

measured by EEG).

State anger. To further test the motivational direction model of asymmetrical frontal

cortical activity, experiments have been conducted in which anger was manipulated. Harmon-

Jones and Sigelman (2001) found that individuals who were insulted evidenced greater relative


left frontal activity than individuals who were not insulted. Additional analyses revealed that

within the insult condition, reported anger and aggression were positively correlated with relative

left frontal activity. Neither of these correlations was significant in the no-insult condition.

Harmon-Jones, Peterson, and Harris (2009) conceptually replicated the above research and

extended it by showing that social rejection causes increased relative left frontal activity that is

associated with anger and jealousy. Jensen-Campbell, Knack, Waldrip, and Campbell (2007) and

Verona, Sadeh, and Curtin (2009) also replicated Harmon-Jones and Sigelman‟s (2001) results,

with the latter group extending them by showing that an impersonal stressor (high pressure air

blasts assigned by a computer) also evokes greater relative left frontal activity, which correlates

with aggression in an “employee-supervisor” lab task.

Other work replicated these results and revealed that state anger evokes both increased

left and decreased right frontal activity. In the same experiment, when participants were first

induced to feel sympathy for a person who insulted them, this reduced the effects of insult on left

and right frontal activity (Harmon-Jones, Vaughn-Scott, Mohr, Sigelman, & Harmon-Jones,

2004), consistent with the idea that sympathy reduces aggression (Miller & Eisenberg, 1988).

Independent Manipulation of Approach Motivation within Anger. In the experiments just

described, the designs were tailored in such a way as to evoke anger that was approach oriented.

Although most instances of anger involve approach inclinations, it is possible that not all forms

of anger are associated with approach motivation. To manipulate approach motivation

independently of anger, Harmon-Jones, Sigelman, Bohlig, and Harmon-Jones (2003) performed

an experiment in which the ability to cope with the anger-producing event was manipulated.

Based on past research that has revealed that coping potential affects motivational intensity

(Brehm, 1999; Brehm & Self, 1989), it was predicted that the expectation of being able to take


action to resolve the anger-producing event would increase approach motivational intensity

relative to expecting to be unable to take action. In support of this prediction, angered

participants who expected to engage in the approach-related action evidenced greater left frontal

activity than angered participants who expected to be unable to engage in approach-related

action. Moreover, within only the action-possible condition, participants who evidenced greater

left frontal activity in response to the angering event also evidenced greater self-reported anger

and engaged in more approach-related behavior.

The research of Harmon-Jones, Sigelman et al. (2003) suggests that the left frontal region

is most accurately described as a region sensitive to approach motivational intensity. That is, it

was only when anger was associated with an opportunity to behave in a manner to resolve the

anger-producing event that participants evidenced the increased relative left frontal activation.

The effect of approach motivation and anger on left frontal activity has also been produced using

pictorial stimuli that evoke anger (Harmon-Jones, Lueck, Fearn, & Harmon-Jones, 2006).

The above findings may suggest that relatively greater left frontal activity will occur in

response to an angering situation only when there is an explicit approach motivational

opportunity. However, it is possible that an explicit approach motivational opportunity is not

necessary for increased left frontal activity to anger to occur, but that it only intensifies left

frontal activity. In other words, other features of the situation or person may make it likely that

an angering situation will increase approach motivational tendencies and activity in the left

frontal cortical region. For example, individuals who are chronically high in anger may evidence

increased left frontal activity (and approach motivational tendencies) in response to angering

situations that would not necessarily cause such responses in individuals who are not as angry.

This prediction is predicated on the idea that individuals high in trait anger have more extensive


associative networks for anger than individuals with lower trait anger, and that anger-evoking

stimuli should therefore activate parts of the network more readily in individuals high in trait

anger (Berkowitz, 1993; Berkowitz & Harmon-Jones, 2004).

In the study, participants were exposed to anger-inducing pictures (and other pictures)

and given no explicit manipulations of action expectancy (Harmon-Jones, 2007). Across all

participants, a null effect of relative left frontal asymmetry occurred. However, individual

differences in trait anger related to relative left frontal activity to the anger-inducing pictures,

such that individuals high in trait anger showed greater left frontal activity to anger-producing

pictures (controlling for activity to neutral pictures). These results suggest that the explicit

manipulation or opportunity for approach motivated action may potentiate the effects of

approach motivation on relative left frontal activity, but may not be necessary.

Additional support for the role of approach motivational intensity being involved in the

anger and frontal asymmetry relationship comes from a recent experiment in which body posture

was manipulated to influence approach motivational intensity (Harmon-Jones & Peterson, in

press). Past research has suggested that manipulated body postures can affect behavior, with

slumped postures leading to more ―helpless behaviors‖ (Riskind & Gotay, 1982). Similarly,

lying flat on one’s back may be antithetical to approach motivation, or the urge to move toward

something. In the experiment, participants were randomly assigned to an upright or reclined

body position, and then they received neutral or insulting interpersonal feedback, as in previous

research (Harmon-Jones et al., 2004). For participants who received the feedback while upright,

results replicated past research, with the insulting feedback causing greater relative left frontal

activation than the neutral feedback. In contrast, participants who were insulted while in a

reclined position did not show the typical increase in relative left frontal activation. This research


further supports the role of approach motivation in the anger-related left frontal activity

relationship.

Anger and Withdrawal Motivation. The reviewed research suggests that greater relative

left frontal activation is associated with anger because anger is often associated with approach

motivation. This conclusion is most strongly supported in the studies by Harmon-Jones et al.

(2003, 2006) that showed that reducing the approach motivational intensity of anger reduces

relative left frontal activation.

Is it possible for anger to be associated with an increase in right frontal activation? Based

on the motivational direction model, we would expect that anger may be associated with right

frontal activation if the anger evoked withdrawal motivational tendencies. However, anger may

be evolutionarily prepared to evoke approach motivation, and it thus may be difficult for anger to

activate withdrawal motivation. Indeed, research with infants (Lewis, Sullivan, Ramsay, &

Alessandri, 1992) and non-human animals (Blanchard & Blanchard, 1984) suggests that anger is

predominantly associated with approach motivational tendencies.

Despite the above caveats, it is possible that anger may be associated with withdrawal

motivation when the angering situation also evokes punishment concerns. If the expression of

anger is perceived to be socially inappropriate, some individuals may withdraw from the context

rather than evidence approach-oriented anger.

To test these ideas, Zinner, Brodish, Devine, and Harmon-Jones (2008) created a social

context in which the experience of anger was considered socially inappropriate. Because of the

norms discouraging public expressions of racial prejudice (Plant & Devine, 1998), some

individuals may become angered by the pressure to behave in a ―politically correct‖ manner but

also want to avoid expressing anger, leading them to withdraw. Indeed, our research revealed


this to be the case in a situation in which individuals were pressured to behave in a ―politically

correct‖ manner. In this situation, anger related to greater relative right frontal cortical activity.

Moreover, anger was associated with anxiety suggesting that this situation had evoked concerns

of punishment among individuals who became angry. These results support the idea that anger

was associated with relative right frontal activation because of withdrawal motivation.

Conclusion

This chapter provided a selective review of some of the most researched neural substrates

of approach and avoidance motivation. The research suggests that the amygdala is involved in

determining motivational relevance. The anterior regions of the nucleus accumbens are generally

involved in appetitive processes and the posterior regions of the nucleus accumbens are generally

involved in avoidance processes. The orbitofrontal cortex is involved in both approach and

avoidance motivation, with the medial areas being more involved in approach-related

motivational processes and the lateral areas being more involved in avoidance-related

motivational processes. The anterior cingulate cortex is critically involved in the detection of

response conflict and as such may assist in resolving approach-approach, approach-avoidance,

and avoidance-avoidance conflicts. Finally, the dorsolateral prefrontal cortex is asymmetrically

involved in motivational direction, with the left dorsolateral prefrontal cortex being involved in

approach motivational processes and the right dorsolateral prefrontal cortex being involved in

withdrawal motivational processes. Although the current research clearly supports the above

summary, it is important to note that plasticity exists throughout the brain and life experiences

can modify how given brain regions process positive and negative emotional information, as

Reynolds and Berridge (2008) have shown within the nucleus accumbens.


As noted above, each structure is densely connected with other structures and infused

with multiple neurochemicals. These connections and chemicals will likely prove important in

unraveling the role of the brain in motivation. Ultimately, the story of the neural substrates of

motivational direction will become more complex as scientists develop better techniques to track

the fleeting communications among neurons and chemicals and better theories and behavioral

methods to understand approach and avoidance motivation. Unraveling how self-enhancement

and self-protection processes unfold within the neural circuits devoted to approach and

avoidance motivation will undoubtedly assist in better understanding this neural circuitry, as

these self processes play significant roles in our everyday lives (Alicke & Sedikides, 2009).

Moreover, the investigation of neural circuits involved in these self-processes may assist in

testing competing psychological explanations of processes underlying self-enhancement and

self-protection (Beer & Hughes, 2009).


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