Inhibition

Chris Jung

Department of Integrative Physiology

09/23/08

Outline

• Prefrontal Neurons Coding Suppression of Specific Saccades– Hasegawa RP, Peterson BW, and Goldberg ME

• The role of inhibitory control in forgetting unwanted memories: A consideration of three methods. – Anderson MC

• In Opposition of Inhibition– MacLeod CM, Dodd MD, Sheard ED, Wilson DE, and

Bibi U

Prefrontal Neurons Coding Suppression of Specific Saccades

Hasegawa, R.P., Peterson, B.W., & Goldberg, M.E. (2004).

Neuron, 43, 415-425.

• Introduction• Methods• Results• Conclusions

Introduction

• Monkey and humans that do not avoid looking at something can be seen as socially offensive, unacceptable.

Introduction

• Eye fixation is an active process• Two mechanisms have been proposed:

– An inhibition of the saccadic system by the fixation system

• When fixation occurs, the threshold for evoking saccades increases by electrical stimulation from the frontal eye field (FEF) and the superior colliculus, which are apart of the fixation system

– Some neurons of the FEF are activated if a stimulus is present to cancel the saccade such as in a “go/no go task”

Methods• Caudal part of dorsolateral prefrontal

cortex

• Match/Non Match Task

Figure 1

• Look neurons– Enhanced

response if the monkey knew a priori of a saccade target

– 10% of samples

Sample Period: 3 Different Responses

• Don’t look neurons– Enhanced

response if the monkey knew a priori of a non-saccade target, or to avoid looking at the original stimulus

– 10% of sample

Sample Period: 3 Different Responses

Sample Period: 3 Different Responses

• Pure visual neurons– No difference

between tasks– 80% of sample

Delay Period: 3 Different Responses

• Look neurons 53%– Greater activity if the stimulus was to saccade

to the original sample stimulus

• Don’t look neurons 19%– Greater response if the stimulus was to not

look where the sample stimulus was

• Memory neurons 28%– Responded equally to both stimuli– Believed to be working memory

• The authors report to have located neurons that help to plan a behavior or suppress it, whether immediately or during the delay.

• Temporal progression– Neurons often switched functions during the

different phases of the test

Conclusions

The role of inhibitory control in forgetting unwanted memories: A consideration of

three methods

Anderson, M.C. (2005). In C. MacLeod & B. Uttl (Eds.) Dynamic Cognitive Processes (pp. 159-190). Tokyo: Springer-Verlag.

• Central claim• Retrieval-induced forgetting• Directed forgetting • Conlusions

Central claim:

• Humans can control memory by overriding prepotent responses to unwanted memories

Figure 1

Within-Category Retrieval-Induced Forgetting Study

Figure 2

Retrieval-Induced Forgetting

• Inhibition or response competition theory of interference?

• Response competition theory of interference– Target will suffer because increased competition

from the alternative response is strengthened– Practiced items become so strongly linked to the

practice cue that they block other examples

Retrieval-Induced Forgetting

• Inhibition or response competition theory of interference?

• Inhibition– Recall specific

• Retrieval practice impairs the delayed recall of competing items

– Cue independence• Retrieval induced forgetting when novel cues are used

Directed Forgetting

Roach--Ordeal

Directed Forgetting

• Dorsolateral prefrontal cortex• Lateral premotor cortex

Conclusions

• Controlled inhibition may be recruited for our goals, regardless if the goals are to forget (Flexible inhibition hypothesis)

• Can help to explain the directed forgetting and retrieval induced forgetting

In Opposition of InhibitionMacLeod, C. M., Dodd, M. D., Sheard, E. D.,

Wilson, D. E., & Bibi, U. (2003).

In B. H. Ross (Ed.), The Psychology of Learning and Motivation, Vol. 43 (pp. 163-214). San

Diego, CA: Academic Press.

• Problem

• Examples

• Proposed Solution

The Main Problem:

“…the concept of inhibition at the cognitive level cannot derive directly from the concept of inhibition at the neural level.”

• The term “inhibition” is too flexible of a term

Negative Priming

• They report:– No conclusive evidence that inhibition can

explain negative priming.

RED

GREEN

• Automatic memory retrieval– If there is disagreement between the task at

hand and a recent memory, this will take longer because you need to resolve the conflict

Inhibition of Return

Inhibition of Return

Inhibition of Return

• Inhibition of Return – Past researchers have concluded that there is

an inhibitory mechanism to look towards the area of a stimuli that was already presented

• Attentional Momentum Hypothesis– MacLeod et al. believe that attention can be

more easily and faster oriented in a direction of a location in which it already has been rather than shifting to another location

• Inhibition is too broad of a term• The terms “interference”, “selective rehearsal”

should be used instead depending on the task• Inhibition has been labeled as below baseline

performance.• For a decrement in baseline performance, the

term “cost” should be used.• For an increment in baseline performance, the

term “benefit” should be used.

• Two mechanisms that are inhibition free:– Automatic memory retrieval

• If there is disagreement between the task at hand and a recent memory

– Conflict resolution