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Executive Control

• Chris Rorden• Executive Control, Problem Solving

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Prefrontal Cortex

Prefrontal Cortex are all regions of the frontal lobe exceot the motor and premotor regions.

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Dolphin Brain

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Phineas Gage– Injured in 1848– Foreman for construction– Railway tamping iron accidently

launched through skull1.1 meters longOver 6kgLanded 25 meters behind himTreated by Dr John Harlow

– Lived until 1860

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Phineas Gage

Harlow (1868) wrote report on Gage Before

– efficient foreman– well-balanced mind– shrewd smart business man

After– Fitful– Irreverent, and grossly profane– Little deference for his fellows– Impatient and obstinate, yet capricious and vacillating– Poor planning

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Frontal Lobotomy (Leucotomy)

Moniz (1936) Severed frontal lobe nerve fibers

– 20 patients– Anxiety, depression, schizophrenia– ‘Improvement’ subjective– Moniz was already famous for X-ray angiography,

this added acceptance for his new work In USA, Freeman became advocate

– Reported substantial improvements– Noted that patients lost some spontaneity, sparkle

5,000 lobotomies performed in 1949 alone Moniz won 1949 Nobel prize for medicine Popularity only declined with introduction of

neuroleptic drugs.

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Early criticism of lobotomy

Hoffman (1949)– "these patients are not only no longer

distressed by their mental conflicts but also seem to have little capacity for any emotional experiences - pleasurable or otherwise. They are described by the nurses and the doctors, over and over, as dull, apathetic, listless, without drive or initiative, flat, lethargic, placid and unconcerned, childlike, docile, needing pushing, passive, lacking in spontaneity, without aim or purpose, preoccupied and dependent."

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Was lobotomy effective?

Tooth et al. (1961)– 9,284 patients examined– 41% improved– 28% minimally improved– 25% no change– 2% worse

However, about 30% spontaneous recovery rate.

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Classic consequences of frontal damage

Frontal lobe patients can show normal IQ on standard tests. However,they are typically impaired in many functions:– Poor control of reasoning, planning and emotions– Poor mental flexibility: perseveration– Frontal lobe modulates functions of other regions– Disinhibition: poor control of emotions– Perseveration: e.g. trouble stopping action once

initiated, e.g. dialing 999.

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Consequences of PFC damage Ventromedial: Cofabulation, poor creativity, poor attention, inappropriate emotions and behavior. Orbital Fibers: (Connects to amygdala and hypothalamus): inappropriate emotions. VLPFC: Language impairments DLPFC: Motor impairments: perseveration, incoordination, hypokinesia

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Real world difficulties

Goel et al. (1997) describes difficulty in financial planning task.

Asked to evaluate different costs for family and economize

Control patients came up with realistic suggestions (e.g. hand down clothes to younger children).

Patients were less practical:– PATIENT: Shelter was the biggest expense. Now, if they

eliminate that, $10,800 they save a year.– EXPERIMENTER: But you need a place to live.– PATIENT: Yes. Course I know a place that sells tents cheap.

You can buy one of those.

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A: Tower of London

Shallice (1982)– Two tasks:

Tower of London WAIS block design

– Two patient groups Parietal Frontal

Start Position Goal 2 (2 moves) Goal 10 (5 moves)

WAIS blocks

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B: Results

Shallice (1982)– Frontal patients:

Impaired with Tower of London (requires planning) Fine with WAIS blocks

– Parietal Patients Fine with Tower of London Impaired with WAIS blocks (spatial skills)

Conclusion: double dissociation highlights frontal deficit in strategic planning.

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A: Thompson-Schill et al., 1998

Inferior Frontal Gyrus – Language comprehension intact following

Left IFG damage.– However, neuroimaging suggests region is

activated in verb generation.

IFG aka VLPFC

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B: Verb generation task

Present noun and ask participant to say what object does or what it is used for.

Low selection nouns: few relevant verbs: ‘scissors>cut’, ‘kite>fly’

High selection nouns: ‘string’ has many correct answers: ‘swing’, ‘tie’, ‘hang’

High selection nouns appear easier: many chances of providing a correct answer.– But we must choose between competing responses.

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C: Patient Groups

4 groups:– Left IFG– Left frontal (IFG spared)– Right frontals– Controls Lesion incidence for

Left IFG patients

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D: Results/Conclusions

Results:– Left IFG impaired when faced with high

selection nouns, fine with low selection nouns.– BA44 correlated with deficit.

Left IFG deficit is not in semantic retrieval per se:– They have no problem retrieving

correct answer to low selection nouns. Left IFG required to select between

competing semantic information.

High SelectionLow Selection

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Verb generation

Hillis et al. describe patients who had hypoperfusion of the left posterior inferior frontal and precentral gyri.

Impaired writing names of verbs, but fine for nouns. Deficits eliminated with perfusion intervention.

Case 1

Case 2

before intervention after intervention60 picturesof nouns

30 picturesof verbs

50:58 10:28

56:48 16:21

Verbal : Written Naming

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A: Task switching

Perseveration is a common feature of frontal lobe patients: difficulty stopping a task.

What portions of the frontal lobe are responsible for this?

Aron et al. (2003) examined this with a stop-signal task.

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B: Design

On each trial, arrow presented.– Left arrow: press left button– Right arrow: press right button

On a few trials (25%) beep occurs after arrow. This means you should not press a button.

The time between arrow and beep varies, allowing us to calculate how much time is required to repress a planned response.

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C: Patients

18 patients with right focal frontal lesions– For each patient, the damage in 5

anatomical regions was measured.

medial orbital IFG MFG SFG

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D: Results

Correlation analysis: relate patient lesion size in each region to deficit.

Damage to the right inferior frontal gyrus (IFG) best predictor of deficit.– In particular, pars

triangularis damage BA45 Poor correlation in other

regions.

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Swainson et al. (in press)

How about healthy people?Swainson et al. (in press,

Journal of Cognitive Neuroscience) has shown similar right hemisphere IFG activity in healthy adults during response suppression.

Additional evidence of cortical assymetry.

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A: Knight and Grabowecky (1995)

P30 is initial response found 30ms after presentation of auditory stimulus

P30 occurs regardless of whether participant is required to make response.

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B: Results

Parietal patients intact P30 Temporal patients:

reduced P30 (auditory cortex damaged)

Frontal patients show enhanced P30 (stronger response than in controls)

Control SignalLesion Signal

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C: Conclusions

Study indicates failure to inhibit irrelevant information.

Suggests early role of frontal cortex in inhibition of redundant sensory information.