Psych 414; 4-23-09; Lecture 24: EXECUTIVE FUNCTION: *Note that the ?decider? is placed in prefrontal cortex? *Phineas Gage?metal rod through head in railwork accident. Rod goes through prefrontal cortex. This brain damage change his disposition/planning. Dysexecutive syndrome?occurs w damage to prefrontal cortex. Inappropriate behavior/disinhibition; poor planning/judgment, etc. (W.R. another famous pt. Had tumors in prefrontal corex=produce sx?s) Q: What happens when you damage your frontal lobes? A: Working memory impairment Clinical test for frontal lobe dysfunction=Wisconsin card sort task(every card have 1 of 4 objects on it, 1 of 4 different colors, different number of objects on it. Start with one ?rule? for classifying cards. Test=figure out what the rule is. Present card, ask what category fits, get feedback of y/n. Use shape, number of objects, or color as the rule. Allow P to guess until figure out rule. Once person gets three in a row correct *you, without telling them, change the rule. **most ppl recognize the rule has been changed and will alter responses **If have frontal lobe damage, perform normally in determining first rule. BUT, terrible at switching from this original rule. **Monkeys, young children, & schizo?s all differ in prefrontal cortex function from ?normal? adults. (In schizo?s, not receive normal amt dopamine=affect prefrontal cortex) Have trouble ?switching? from one rule/goal to another? (test with Wisconsin card sort variant When switch rule this time, can do so either intradimensionally or extradimensionally. Pt=both shifts require inhibition of previous rule. Front pts perform worse w extradimensional shift because have to also change what dimension pay attn to=evidence, yes, pts have trouble ?switching.? Have trouble inhibiting (?tamping down?) previously used rule? (test with Stroop task. (word/color ink). Task=name color of ink word is printed in. This is not a well-practiced activity. Reading words, however, is. Neutral=non-color word (?dog?) Congruent=color name and color ink are same Incongruent=color name and color ink are different **Frontal pts have VERY hard time with incongruent condition =evidence frontal damage=inhibition problems Trouble in generating responses: Letter fluency task that frontal pts impaired in(List as many words as can beginning with letter ?F?? DV=how many words generated (Healthy older controls ~ave 12-14 items vs. prefrontal pts ~4-6 items *also produce repetitions??fire, found, fox, fire, folder, found?) Trouble selecting among many competing responses(another test=?what do you do with a?computer?? For some objects, only one use (scissors=cut; typewriter=type) For other objects, many possible uses (computer=email, type, etc.) **need to select one of many possible actions** Prefrontal pts do well if only one use The more possible responses to choose from, the more metabolic activity seen in the PFC (so PF pts worse here) *pathways are competing. If one pathway is activated, inhibits the other. Activated pathway is the one that ends up generating the end response. *Because so well-practiced at reading words, synaptic weights are bigger overall than those leading from the ink color. ? Word? ends up producing end output. *If given instruction of ?name ink? ?turns on? ?some representation may prime less well-practiced pathway *Prefrontal cortex is most important in performing tasks that require responses that are not well-learned. *Does absence of PFC lead to apathy? N-back task: Working memory task. Requires both memory and updating. Need to mentally compare stimulus with what saw 2 steps ago (if N=2), but need to continuously update which letters ?were two stimuli ago.? Ex. have representation of ?seeing a B when it was preceded by an A??then see an A, copy over memory? AXCPT task(Say yes if ?X??unless preceded by an ?A??many ?X?s? so get used to saying yes to X. Rely on memory to inhibit ?yes? if preceded by memory of an A?inhibit that pathway.
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