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4: Executive Control

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Prefrontal Cortex are all regions of the frontal lobe exceot the motor and premotor regions. ... Low selection nouns: few relevant verbs: scissors cut', kite fly' ... – PowerPoint PPT presentation

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Title: 4: Executive Control


1
4 Executive Control
  • Chris Rorden
  • Lecture 4
  • Executive Control, Problem Solving

www.mricro.com
2
Prefrontal Cortex
  • Prefrontal Cortex are all regions of the frontal
    lobe exceot the motor and premotor regions.

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  • Phineas Gage
  • Injured in 1848
  • Foreman for construction
  • Railway tamping iron accidently launched through
    skull
  • 1.1 meters long
  • Over 6kg
  • Landed 25 meters behind him
  • Treated by Dr John Harlow
  • Lived until 1860

9
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

10
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.

11
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."

12
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.

13
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.

14
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

15
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.

16
A Tower of London
WAIS blocks
  • 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)
17
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.

18
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
19
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
    scissorsgtcut, kitegtfly
  • 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.

20
C Patient Groups
  • 4 groups
  • Left IFG
  • Left frontal (IFG spared)
  • Right frontals
  • Controls

  • Lesion incidence for Left IFG patients

21
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 Selection
  • Low Selection

22
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.
  • Verbal Written Naming
  • before intervention
  • after intervention
  • 60 pictures
  • of nouns
  • 30 pictures
  • of verbs
  • Case 1
  • Case 2
  • 5058
  • 1028
  • 5648
  • 1621

23
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.

24
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.

25
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
26
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.

27
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.

28
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.

29
B Results
Control Signal Lesion Signal
  • Parietal patients intact P30
  • Temporal patients reduced P30 (auditory cortex
    damaged)
  • Frontal patients show enhanced P30 (stronger
    response than in controls)

30
C Conclusions
  • Study indicates failure to inhibit irrelevant
    information.
  • Suggests early role of frontal cortex in
    inhibition of redundant sensory information.

31
Key Readings
  • Stop-signal inhibition disrupted by damage to
    right inferior frontal gyrus in humans.
  • Aron et al. (2003) Nature Neuroscience, 6,
    115-116.
  • Review of executive function
  • Fuster (2000) Experimental Brain Research, 133,
    66-70.
  • IFG required for accurate verb generation
  • Thompson-Schill et al. (1998) Proc. Natl. Acad.
    Sci. USA, 95, 15855-15860.
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