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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 Sample Period: 3 Different Responses • 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 nonsaccade target, or to avoid looking at the original stimulus – 10% of sample 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 Conclusions • 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 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 Inhibition MacLeod, 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