PHYSIOLOGY OF HIGHER FUNCTION OF BRAIN

Integrative teaching bloc 16Dr. Swanny, MSc

ObjectivesDescribe the functions of the different areas of the brain.Distinguish between different types of memory and describe the roles of different brain regions in memory.Describe the location of the hypothalamus and explain the significance of this region.Explain the role of the limbic system in the control of behavior and emotion.

IntroductionHIGHER FUNCTION OF BRAINNeurobehavioral function.

What is the part of brain?What is the function ?How is the mechanism ?

Neuronal part of brainCEREBRAL CORTEX :the functional part of cerebral cortex a thin layer of neurons 2 to 5 mm in thickness covering the surface of all convolutions of cerebrum a total area of one quarter square meter contains about 100 billions neurons.

Function of cerebral cortexIntellectualLearningMemory

Behavioral and motivationalThe control of behavior is the function of ENTIRE nervous system wakefulness, sleep cycle.Brain control the level of activity.Motivational drives control of learning process, feeling of pleasure and punishment performed by basal regions of brain LIMBIC SYSTEM.

Behavioral State System: Emotion and MotivationThe link between emotions and physiological functionsThe amygdala is the center of emotion in the brainStimulus to Cerebrum- creates perception, limbic creates emotion, cerebrum becomes aware of emotion while hypothalus stimulates multiple responses

Behavioral/Cognitive State : MotivationDefined as internal signals that shape voluntary behavior (related to survival or emotions)Some states known as drives create increased arousal, goal-oriented behavior, and disparate behavior to achieve the goal.Works with autonomic and endocrine responses to maintain homeostasisMotivated behaviors stop SatietyPleasure is related to addictive behaviors which can be changed if given a different motivation.

Behavioral State System: MoodsSimilar to emotions but longer-lasting- related to sense of being, not purely psychological, related to sense of well-being and proper neurotransmitter functionMood disordersFourth leading cause of illness worldwide todayDepression Sleep and appetite disturbancesAlteration of mood and libidoAntidepressant drugs alter synaptic transmission allow a neurotransmitter to remain at the synapse longer, change the receptor, or the amount of NT released.

Cognitive State: Learning and MemoryLearning has two broad typesAssociative links two stimuli or a stimulus to a behaviorNonassociative- change behavior due to repeated exposureHabituation do not respond to an irritant stimulus, filters out insignificant stimulusSensitization- enhanced response to irritant stimulus, helps avoid harmful stimuliMemory has several typesShort-term and long-term- combined by working memory, consolidation turns short-term into long term. Changes in synaptic connections are requiredReflexive and declarative- requires unconscious (procedural) or conscious recall (infer, compare, evaluate). Declarative can become reflexive

Brain Function: Memory Processing

Brain Function: LanguageCerebral processing of spoken and visual language Damage to Wernickes causes receptive aphasia- unable to understand spoken or visual informationDamage to Brocas area causes expressive aphasia- can understand information but cannot speak or write in proper order, are aware of mistakes

Functional Divisions - Cerebrumprimary sensory or motor areas secondary sensory or motor areas association cortex

Functional Divisions - Cerebrumprimary sensory areas somatosensory cortex - postcentral gyrusvisual cortex - occipitalauditory cortex - temporalolfactory cortex - olfactory bulbgustatory - part of somatosensory primary motor area - precentral gyrus

Cortical Areas

Neocortical Layers (I-VI)

Organization of nerve fibers within layer of cortexMolecular layerExternal granular layerPyramidal cells layerInternal granular layerLarge pyramidal cell layerFusiform or polymorphic cells.

Granular/ stellate cell short axon, function as intracortical interneurons.Pyramidal and fusiform cells long nerve fibers give rise to almost all output fibers from cortex. They also give rise to most of large subcortical association fiber bundles that pass from one major part of brain to the other.

Function of fibersHorizontal fibers extend between adjacent areas of cortex.Vertical fibers to and from cortex to lower areas of brain and to spinal cord or to distant regions of cerebral cortex through the long association bundles.

Sensory,association,and motorcortex

Layer IV vs.Layer V

Layer I, II and III perform most of the intracortical association functions.Layer IV incoming sensory signals terminate in this layer.Layer V, VI output signals leave cortex from neurons located in these layer. The very large fibers to brain stem and cord arises in layer V. The fibers to thalamus arises from neuron in layer VI.

Brain Function: complex processing and responses

Hemispheric Dominance (Lateralization)90% of humans are right handed - left hemisphere is dominant for handedness many animal species also show handedness 98% of humans - comprehension of spoken and written word and motor control of speech is in the left hemisphere

Hemispheric Dominance - Humanleft hemisphere (analytical)

speechwritingmain language centercalculationright hemisphere (creative)

spatial constructionnonverbal ideationsimple language comprehension

Hemispheric Dominancehemispheric damage in the adult nearly permanent loss damage in the child (up to age 3 yrs) results in functions being assumed to variable extents by the other hemisphere plasticity some hemispheric differences are present before birth, so anatomically predetermined

class demo

MemoryEncoding, sorting, storage, retrieval, and transfer of acquired verbal and nonverbal sensory experiences, concepts, and sensorimotor behavioral patterns. Memory is the substrate for all higher mental functions and the prerequisite for learning and adaptive behavior.

Memory & LearningLearning: the process by which we and other animals acquire knowledge about the world. Memory: the retention or storage of that knowledge.

Alternate DefinitionsLearning: the acquisition of an altered behavioral response due to an environmental stimulus.Memory: the process through which learned information is stored.Recall: the conscious or unconscious retrieval process through which this altered behavior is manifest.

Classification of Memory Formsclassified by how information is stored and recalled: explicit (declarative) memory implicit (procedural) memory

Explicit/Declarative Memorystorage (& retrieval) of material that is available to the conscious mind"what" the world is aboutknowledge of people, places, and things that are available to the conscious mindinvolves evaluation, comparison, and inferencecan be recalled by a deliberate act of recollecting birth date, Social Security Numberfrom single or multiple trials

Implicit/Procedural Memorynot available to the conscious mindinvolves skills and associations that are acquired and retrieved at an unconscious level"how" to do thingsmotor or perceptual skills unavailable to conscious mindacquired slowly through repetitionexpressed primarily by improved performancesigning your name or riding a bicycle

Implicit/Procedural Memory (cont.)motor memory: physical acts learned through multiple repetitions to the point where conscious thought is not required for their performanceother types emotions associated with a memory, etc.

Subdivisions of Human Memory

Time Domains of Memoryboth explicit and implicit memories have short-term forms and long-term (nearly permanent) forms (more below)consolidation from short-term to long-term requires protein synthesis (and sleep!)recently acquired memories are more easily disrupted than older oneslong-term memories gradually diminish with time, especially with disuse

Time Domains (3) of Memory1. immediate memory lasts a few seconds, large capacity, all sensory modalities, awareness of environment2. short-term memory - seconds to minutes; e.g. strings of digits; limited storage capacity, then either lost or transferred to more stable memory forms; rapid retrieval

working memory - form of short-term conscious memory used to carry out sequential actions toward a goal, i.e. searching for a lost object; not stored.

Time Domains of Memory3. long-term memory - days, weeks, or a lifetime; requires transfer (consolidation) from short- term; depends on changes in synaptic strength or synapse numbers; vast capacity, rapid recall intermediate-term memory - name used by some to describe the memories that overlap short-term and long-term memory

Time Domains of MemoryConsolidation of memory from short-term to long-term:

hippocampus is required for memory consolidation

requires protein synthesis

requires sleep REM and possibly SWS at least in animals

Short-termmemory storeLong-termmemory storeSearch and read outSimplified Model of Memory Processes During LearningInputOutputconsolidation

Proposed Anatomic Correlates of Memoryexplicitimmediate: prefrontal cortex and dorsal medial thalamus or primary & secondary sensory cortex short-term: hippocampus and temporal lobe, mammillary bodies, midline diencephalic structures long-term: diffuse throughout the cerebrum

Anatomic Correlates of Memoryimplicit motor: cerebellum, basal ganglia, secondary motor cortex emotion-associated: amygdala

Mechanisms of Memoryimmediate and short-termreverberating circuits (minutes)altered electrical excitability changes in [Ca++] and altered ionic conductances due to neurotransmitters (minutes to hours)transient changes in receptorslong-term potentiation (LTP)long-term depression (LTD)

Mechanisms of Memorylong-termlong-term potentiation (LTP)long-term depression (LTD)gene expressionprotein synthesis-mediated changesnew dendritic spinesreplication and/or strengthening of synaptic contactsformation of new neuron-to-neuron contacts

Dendritic Spines: Young vs. Old Animals

Long-Term Potentiation (LTP)strengthening the synaptic connections between activated neurons, especially in the hippocampus, cerebral cortexpostsynaptic potential amplitudes are increased by tetanic stimulation of the presynaptic terminal (50 Hz, 1 sec) enhanced response can last for minutes to hours to days, perhaps longercan selectively enhance one input to a neuron without changing the strength of other inputs

Long-Term Potentiation

Long-Term Depression (LTD)weakening of established synaptic connections between activated neurons"turning off" LTPresults from reversing the biochemical pathways that produced LTPactivated by low frequency activation of the same or different presynaptic terminalseen especially in cerebellum

Long-Term Depression

Ca++ Trigger of Both LTP & LTD

Memory DisordersAmnesia (or pathological forgetting) Anterograde amnesiaRetrograde amnesia

Hyperthymestic syndrome

Memory DisordersAnterograde amnesia - deficit in registration and storage of new recent or long-term memories Korsakoff syndrome (chronic alcoholics) damage to mammillary bodies & medial thalamus, confabulationKlver-Bucy syndrome bilateral lesion of hippocampal/temporal lobe; patient H.M.head trauma and/or impaired consciousness

Memory DisordersRetrograde amnesia - deficit in ability to retrieve memories head traumaimpaired consciousnessAlzheimer's diseaseelectroconvulsive therapy Clinical amnesia cases typically show a mix of anterograde and retrograde amnesia

Memory DisordersHyperthymestic syndrome - deficit in ability to forget or suppress memories Details of events going back 30 yearsPatient describes being consumed by the "burden" of memories that were "non-stop, uncontrollable and totally exhausting." Normal IQTwo cases reported

SpeechCommunication or expression of ideas or information through vocalization of standardized sounds (and/or words) with accepted associations

Speech In Humans - Left Hemisphere (98%)Broca's area - frontal lobe, secondary motor cortex area for muscles involved in speech Wernicke's area tempero-parietal lobe, secondary auditory cortex Arcuate fasciculus - pathway from Wernicke's area to Broca's area

Language Areas of the Brain

Language Areas of the Brain

Speaking/Repeating a Heard WordPrimary auditory cortex Wernicke's area Arcuate fasciculus Broca's area Motor cortex

Speaking a Heard Word

Speaking a Written WordVisual cortex Angular gyrus Wernicke's area Arcuate fasciculus Broca's area Motor cortex

Speaking a Written Word

Speaking a Written Word

Cerebral Cortex: Outer layer of neurons (1mm thick)Perception: hearing, vision, olfaction, muscles & visceraReasoning, information integrationDirecting voluntary behavior

Lobes of Cerebral Cortex and Associated IntegrationFrontal: voluntary movement, behavior, perceptionParietal tactile sensory Occipital vision Temporal olfactory, auditory & gustatory

Perception: hearing, vision, olfaction, muscles & visceraReasoning, information integrationDirecting voluntary behaviorCerebral Cortex: Outer layer of neurons (1mm thick)

Lobes of Cerebral Cortex and Associated IntegrationFrontal: voluntary movement, behavior, perceptionParietal tactile sensory Occipital vision Temporal olfactory, auditory & gustatory

HYPOTHALAMUS & LIMBIC SYSTEM

EMOTIONEmotion has been a notoriously difficult concept to define. Many psychologists argue that an emotion comprises three different elements:cognitive (thinking) component: an appraisal or judgment feeling (subjective) component: what a person experiences privately action (or, action tendency) component: either an action or, at least, a tendency to an action

Limbic System Functions

Limbic System FunctionsRH more sensitive to emotional stimuli than the left hemisphere (LH). For example, Right amygdala: activated by laughing or crying Right temporal cortex: scanning faces for emotional expression increases activity RH damage: Difficulty interpreting facial expression indicating viewing pleasant or unpleasant scene LH damage: Higher than normal ability to interpret facial expression + greater than even chance to detect lying (60% vs. 50%) RH inactivation: facts, but not strong emotions, of past events remembered RH > LH activity: associated with shyness LH > RH activity: associated with outgoing & fun-loving personality

The Pleasure (Reward) CenterThe nucleus accumbens is the engine of the reward response. And, in recent studies researchers determined that the reward pathway activates pain relief through the release of both opioids, a morphine-like drug produced by the body, and dopamine, a chemical messenger whose effects can be mimicked by amphetamine and cocaine, in this structure. The finding overturns the long-held assumption that the release of dopamine in the nucleus accumbens is associated only with positive experiences.Nociceptive (pain) stimuli depress mood and increase anxiety, irritabilityAntinociceptive (pain relief, analgesic) mechanisms elevate mood and decrease anxiety, irritability

Start (Approach, Repeat Behavior), Stop Signals, Pain and Pleasure

The reward pathway is a neural network in the middle of the brain that prompts good feelings in response to certain behaviors, such as relieving hunger, quenching thirst or having sex, and it thereby reinforces these evolutionarily important drives. However, the circuit also responds to drugs of abuse, such as heroin, cocaine, amphetamine and nicotine, which seem to hijack the circuitry, altering the behavior of its neurons.

Complex Pathways of Emotion and MotivationHypothalamus, limbic & cortex integrationEmotions: pleasure, sexual arousal, anger & fear limited cognitive control "hard to turn off"Motivation: "drives", increase arousal coordinate goal-oriented behaviorMoods: Long term emotional statesDepression, SSRI

Complex Pathways of Emotion and Motivation

Complex Pathways of Learning and Memory

Most Complex Pathways: Language and PersonalityLanguage exchange complex informationWernike's areaBroca's areaPersonalityGenetic componentsExperiencesLearningMemoryPerceptions

ReferencesText book of medical physiology.Guyton & Hall.Human PhysiologyDee ungland SilverthornNeuronal control of mood, emotion and state of awareness. Dianna A. Johnson

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