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Executive processes

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Title: Executive processes


1
Executive processes
  • Properties of executive processes
  • Executive processes coordinate mental activity so
    that a particular goal is achieved
  • They do this by modulating the operation of other
    processes (modulate to guide or modify)
    however, executive processes do not actually
    carry out these activities

2
Executive processes
  • Different types of executive processes
  • Several different types of executive processes
    have been identified. There is currently
    controversy about whether there are several types
    of executive processes or a single type (we are
    assuming several)
  • 1. selective attention. (sometimes called
    executive attention (sustained attention) this
    type of attention is believed to act on the
    contents of working memory and directs future
    mental activity in order to achieve a goal (e.g.,
    driver focuses on traffic signs in order to take
    correct exit)
  • 2. switching attention switching attention from
    one activity to another (e.g., having a
    conversation and driving)
  • Inhibiting information that has been perceived
    (e.g., ignoring music on radio when traffic is
    heavy and one is driving)
  • Scheduling a sequence of activities planning
    the order in which a activities will be carried
    out in order to achieve goal(s) (e.g., order in
    which you will pick up groceries, dry cleaning,
    medications)
  • Performance monitoring review performance to
    ensure it is acceptable (e.g., checking speed
    limit while driving)

3
Executive processes
  • It is generally agreed that the frontal lobes
    play an important role when executive functions
    are carried out
  • The frontal executive hypothesis proposes that
    executive processes are primarily mediated by the
    prefrontal cortex (PFC)
  • PFC anterior to motor cortex (and for some
    authors the premotor cortex)
  • PFC includes dorsolateral PFC, anterior
    cingulate, Brocas area, and the medial and
    orbital regions of the frontal lobes

4
Executive processes
  • Frontal lobes
  • Prefrontal cortex massive network that links the
    motor, perceptual, and limbic (emotional network)
    regions
  • Limbic system include amygdala, cingulate gyrus,
    orbitofrontal cortex and parts of basal ganglia

5
Executive functions
6
Executive functions
  • Frontal lobe
  • Major subdivisions of prefrontal cortex lateral
    prefrontal cortex, ventromedial prefrontal
    cortex, and anterior cingulate

7
Executive processes
  • Frontal lobes
  • About third of cerebral cortex in humans frontal
    lobes are much larger in humans and are much
    larger than in other mammals, especially its
    anterior aspect
  • Frontal lobes separated from parietal lobes by
    central sulcus and from temporal lobes by lateral
    sulcus

8
Kolb Whishaw frontal lobe figure
  • Lateral area 6 premotor cortex
  • Medial area 6 supplementary motor cortex
  • Area 8 frontal eye field

9
Executive processes
  • Dorsolateral prefrontal cortex (areas 9 and 46)
  • Medial frontal cortex (areas 25 and 32)
  • Inferior (ventral) prefrontal cortex (areas 11,
    12, 13, and 14) also called orbitofrontal cortex

10
Executive processes
  • Anatomical properties of PFC that are crucial for
    executive processing
  • Perceptual, motor, cortical, and subcortical
    brain structures project to PFC
  • This makes it possible to combine information
    from diverse sources, thereby enabling complex
    behavior
  • PFC has multiple projections to multiple brain
    structures
  • This permits it to modulate (exert top-down
    guidance) on other neural processes

11
Executive processes
  • Working memory and lateral prefrontal cortex
  • A previous lecture discuss working memory
  • Baddeleys model of working memory was presented

12
Baddeleys working memory model
Visuo-spatial sketchpad
Phonological loop
Central Executive
13
Executive processes
  • Content-based model of working memory
  • This is known as a content-based model of working
    memory because it assumes that different systems
    represent different content
  • Phonological stores linguistic info and
    visusospatial represents visual and spatial
    information
  • Model based on behavioral data reviewed in prior
    lecture

14
Executive processes
  • Process-based models of working memory
  • It has been hypothesized that different regions
    of the PFC are recruited to carry out different
    tasks
  • In other words different processes are associated
    with different brain regions

15
Executive processes
  • Different types of working memory
  • In some tasks a participant is presented a
    stimulus, then is required to internally maintain
    a representation of that stimulus, until a probe
    is presented (maintenance condition)
  • In an n-back task the participant is required to
    keep in mind a stream of stimuli and respond only
    if the stimulus was presented n-back
  • Requires maintenance manipulation

16
Executive functions
  • Illustration of n-back task
  • Note, the need to maintain information in memory
    and manipulate it

17
Executive processes
  • DEsposito et al. (1998)
  • Meta-analysis
  • DEsposito and colleagues performed a
    meta-analysis to investigate content-based and
    process-based accounts of working memory
  • meta-analysis quantitative review of findings
    from several studies

18
Executive processes
  • DEsposito et al. (1998)
  • One might expect based on the content account of
    working memory that the phonological loop might
    be left lateralized and the spatial sketchpad
    should be right lateralized as it is for
    perception
  • To investigate this possibility DEsposito
    categorized studies based on their content
    (spatial, nonspatial)

19
Executive processes
  • DEsposito et al. (1998)
  • Results support the hypothesis that spatial tasks
    tend to be associated with activation of the
    right prefrontal cortex, whereas nonspatial tasks
    are associated with activation of the left
    prefrontal cortex
  • However, there was bilateral activation in many
    studies
  • See top panel

20
DEsposito et al. (1998)
  • Top panel shows active foci for spatial and
    nonspatial tasks (content)
  • Bottom panel shows active foci for maintenance
    and maintenance tasks

21
Executive processes
  • DEsposito et al. (1998)
  • to investigate the process-based account of
    working memory, tasks were categorized as
    requiring maintenance or maintenance plus
    (maintenance manipulation)
  • Results showed that tasks requiring maintenance
    plus had more dorsolateral activation
  • See bottom panel

22
DEsposito et al. (1998)
  • Top panel shows active foci for spatial and
    nonspatial tasks (content)
  • Bottom panel shows active foci for maintenance
    and maintenance tasks

23
Executive functions
  • Stroop test
  • This test assesses the ability to maintain a goal
    and ignore/suppress habitual (prepotent)
    responses

24
Executive functions
  • Stroop effect demonstration
  • in this next slide I want you to name the ink
    colours of the words as rapidly as possible

25
Stroop (slide 1)
  • red yellow blue red
  • green red yellow green
  • blue green red yellow
  • red green red yellow

26
Executive functions
  • Stroop effect demonstration
  • in this next slide I want you to name the ink
    colours of the words as rapidly as possible

27
Stroop (slide 2)
  • red yellow blue red
  • green red yellow green
  • blue green red yellow
  • red green red yellow

28
Executive functions
  • Stroop effect demonstration
  • in this next slide I want you to name the ink
    colours of the colour patches as rapidly as
    possible

29
Stroop (slide 3)
30
Executive functions
  • Stroop effect
  • The increase in time it takes to name of color
    when the word name does not match the color
    versus naming color patches is called the
    color-word interference effect (slide 1
    time/slide 3 slide)
  • Note different versions of the Stroop assess
    interference in slightly different ways

31
Executive functions
Age Dot time (DT) M (SD) Color word time (CWT) M (SD) Interference CWT/DT Errors Color word M (SD)
18-39 11.0 (2.5) 22.1 (7.2) 2.0 (0.6) 0.8 (1.0)
75-74 13.3 (3.6) 32.6 (9.6) 2.6 (0.9) 0.6 (1.2)
Dot time name dot color color word time name
word color
DT Name color of dot CWT Name color of word
designating color
Troyer, Leach, Strauss (2006), 13, 20-35
32
Executive functions
  • Stroop effect
  • Age effects age significantly increases the
    magnitude of the interference effect
  • Gender differences are not always present in the
    interference score
  • The higher the IQ score the lower the
    interference effect

33
Executive functions
  • Stroop effect
  • Standard interpretation of Stroop participant
    must selectively attend to the name of the ink
    color and ignore the word name (of a color)

34
Executive functions
  • Wisconsin Card Sort
  • Used to assess for frontal lobe damage
  • 4 stimulus cards are arranged in front of a
    participant cards vary on 3 dimensions shape,
    color, number
  • Participants are given a deck of cards and must
    match each card with 1 of the stimulus cards, but
    are not told on which dimension they are matching
  • Participants are told right or wrong

35
Executive functions
36
Executive functions
  • Participants are given a deck of cards and must
    match each card to 1 of the 4 stimulus cards
  • Participants guess at first, but since they are
    given feedback, they learn the correct attribute
  • After sorting about 10 cards correctly, the
    examiner changes the attribute without warning
  • Normal participants soon figure out correct
    attribute for sorting

37
Executive functions
  • Frontal lobe patients and normal participants do
    not differ in learning first critical trial, but
    they differ in the ability to switch attributes
  • Normal participants switch after a few trials of
    negative feedback frontal lobe patients are less
    able to switch

38
Executive functions
  • Executive attention is needed whenever multiple
    representations in working memory or multiple
    processes are competing for control of behavior
    and thought
  • In Stroop task there is competition, but this
    sort of competition is a feature of a broad range
    of tasks
  • E.g., it has been shown that naming the color of
    a picture of a banana is slowed when it is not
    yellow (e.g., red)
  • in general when there is an incompatibility
    between an automatic response and a correct
    response you get Stroop-like effects

39
Executive functions
  • Stimulus response compatibility exists when the
    response required is compatible with the way
    people would naturally respond to that stimulus
  • E.g., high pitch respond up low pitch
    respond down
  • E.g., stimulus presented on left or right side of
    display requires a response on same side as
    stimulus was presented

40
Executive functions
  • Stimulus response compatibility is strong and is
    observed even when position of object is
    irrelevant to response (Simon, 1990)
  • E.g., suppose task is to make a right-handed
    response when a circle is presented and a
    left-handed response to a triangle reaction time
    is faster when the circle or triangle is
    presented on the side of the response
  • Interpretation when there is an automatic
    connection between a stimulus and a response,
    little executive attention is required
  • when 2 sources of information are incompatible,
    attention must be paid in order to focus on the
    relevant information and inhibit/ignore the
    irrelevant information

41
Executive functions
  • Cohen and colleagues have developed a neural
    network model of Stroop task
  • It proposes that in addition to initial visual
    perceptual processing of color (occipital lobes)
    and visual words (temporal lobes), two additional
    attentional processes are required

42
Executive functions
  • Stroop effect demonstration
  • in this next slide I want you to name the ink
    colours of the words as rapidly as possible

43
Executive functions
  • 1. attention controller
  • This process keeps track of the task goal this
    is necessary because during incompatible trials
    in the color word condition, the name of the
    color font and the name of the word, which
    designates a color are two competing responses
  • In the color-word condition it does this by
    activating more strongly the processes associated
    with the task goal (in this case the color of the
    word)

44
Executive functions
  • 2. conflict monitor
  • This process monitors the amount of conflict
    between potential responses. When there is more
    conflict as there would be in the word-colour
    condition, the conflict monitor increases
    executive attention

45
Executive functions
  • Stroop effect
  • Other points neuroimaging and lesion studies
    are consistent with hypothesis that frontal lobes
    are associated with Stroop
  • Data also suggest that performance is mediated by
    a more broadly based system

46
Executive functions
  • Neuroimaging evidence
  • Jonides and colleagues (2002) performed a
    meta-analysis of Stroop studies and related
    studies
  • Results showed that the anterior cingulate and
    dorsolateral PFC were activated this is
    consistent with theory because it is known from
    other research that the anterior cingulate is
    activated mediates conflict and the dorsolateral
    PFC is involved in executive attention

47
Executive processes
  • Executive processes effects on longer-term
    memory
  • Individuals with PFC damage may be impaired in
    their ability to organize temporally events in
    memory
  • Milner (1995) performed a recency experiment in
    which participants were required to discriminate
    which of two events was presented more recently

48
Executive processes
  • Memory for temporal order Milner (1995)
  • Participants were presented pairs of stimuli
    (e.g., 2 pictures of objects)
  • Every so often a probe card is presented with ?
  • Task to choose picture with more recently
    presented object

49
Executive processes
  • Milner (1995) Memory for temporal order
  • Experimental condition both objects had been
    presented previously
  • Control condition one picture presented
    previously one picture new (Recognition test)

50
Executive processes
  • Memory for temporal order Milner (1995)
  • 3 groups of participants were tested
  • Controls
  • Unilateral damage to dorsolateral PFC px
  • Unilateral damage to temporal px
  • Px underwent surgery for relief from focal
    epilepsy

51
Milner recency discrimination experiment
  • Top panel shows stimuli used in expt
  • Bottom panel shows that PFC participants were
    impaired relative to other 2 groups on recency
    discrimination test but not on recognition test

52
Executive processes
  • Memory for temporal order Milner (1995)
  • Other findings this experiment was also
    performed with word stimuli
  • Results showed that the effect was lateralized
  • Patients with LHD were more impaired on recency
    discrimination when words were used, whereas px
    with RHD were more impaired with pictures

53
Executive functions
  • Memory for temporal order
  • Milner et al. (1991) performed an experiment in
    which frontal and parietal patients were shown
    pairs of items
  • Occasionally the pairs had a question mark
    between them
  • Participants task was to decide which item had
    been presented more recently
  • When only 1 item had been actually presented the
    test was an item recognition test
  • When both items had been presented, the test
    requires order (and item) information

54
Executive functions
  • Memory for temporal order
  • Patients with frontal lobe damage were impaired
    in their memory for order but not item
    information
  • Patients with parietal lobe damage were impaired
    in their memory for item but not order information

55
Executive processes
  • Memory for temporal order Self-ordered pointing
  • Keeping track of previous experienced events
    (memory for temporal order) has been examined
    using a self-ordered pointing task
  • In this task participant is presented n card with
    n objects depicted on it
  • The same objects are present on each card but
    their order is scrambled from card to card

56
Executive processes
  • Memory for temporal order Self-ordered pointing
  • Task of participant is to point to the a
    different object on each card (one that hasnt
    yet been pointed to)
  • Results
  • Frontal lobe patients made more errors than
    controls discrepency between 2 groups increased
    with n, the number of objects and cards

57
Executive processes
  • Source memory
  • Source memory refers to when we learned a fact or
    the context in which a fact was learned e.g.,
    who told you fact or in what context you viewed a
    face
  • Source memory appears to require frontal lobe
    function

58
Executive processes
  • Source memory
  • Janowsky, Shimamura, Squire (1999)
  • In this experiment participants were taught new
    facts (e.g., The name of the dog on the cracker
    box is Bingo)

59
Executive processes
  • Source memory
  • Janowsky, Shimamura, Squire (1999)
  • 6-8 days later participants were asked to answer
    questions about these newly learned facts and
    other facts that might have been acquired outside
    of the experiment if they recalled the fact they
    were asked questions about when they learned the
    fact (during the previous session or reading,
    school etc.)

60
Executive processes
  • Source memory
  • Janowsky, Shimamura, Squire (1999)
  • Results
  • Controls and frontal lobe patients did not differ
    in recall of facts
  • Frontal lobe participants were impaired in recall
    of source of facts

61
Executive processes
  • Source memory
  • Glisky et al. (1995)
  • Investigated role of memory and executive
    function on item and source memory
  • Neuropsychological tests assessed memory
    (temporal) and executive (frontal) function
  • Performance on these two types of tests was
    weakly correlated

62
Executive processes
  • Source memory
  • Glisky et al. (1995)
  • Study participants heard sentences describing
    events (e.g., The boy went to the store to buy
    apples and oranges)
  • Half were read aloud in mans voice and half in a
    womans voice

63
Executive processes
  • Source memory
  • Glisky et al. (1995)
  • Memory test
  • Item memory recognition test in which pairs of
    studied and unstudied sentences were presented
    together
  • Source memory participant heard sentence read
    aloud in a man or womans voice and decided which
    voice matched the studied sentence

64
Executive processes
  • Source memory
  • Glisky et al. (1995)
  • Results
  • Controls and frontal lobe patients did not differ
    in recall of facts
  • Frontal lobe participants were impaired in recall
    of source of facts

65
Glisky (1995)
  • Source memory relatively more impaired than item
    memory by low frontal function
  • Item memory relatively more impaired than source
    memory by low temporal function

66
Executive processes
  • Executive processes effects on longer-term
    memory
  • Individuals with PFC damage may be impaired in
    their ability to organize temporally events in
    memory
  • Milner (1995) performed a recency experiment in
    which participants were required to discriminate
    which of two events was presented more recently

67
Executive functions
  • Sequencing
  • Many activities of everyday living require people
    to plan and then carry out a sequence of
    activities, which must satisfy certain
    requirements in order to achieve a goal
  • Studies have shown that patients with PFC damage
    are impaired on certain sequencing activities,
    but not all sequencing activities

68
Executive functions
  • Sequencing how is temporal order coded?
  • An important component of sequencing is coding
    temporal order of events
  • Evidence suggests that there are several
    different ways in which temporal order might be
    coded and that the coding of temporal order often
    involves separate processes from the coding of
    item information

69
Executive functions
  • Sequencing how is temporal order coded?
  • An important component of sequencing is coding
    temporal order of events
  • Evidence suggests that there are several
    different ways in which temporal order might be
    coded and that the coding of temporal order often
    involves separate processes from the coding of
    item information

70
Executive functions
  • Sequencing how is temporal order coded?
  • Sternberg, (1966, 1967) compared performance on
    an item recognition (was letter presented?) and
    an order task (what is the next letter?)
  • Item recognition memory set (BGRD) probe (g)
    response (yes)
  • Order task -- memory set (BGRD) probe (g)
    response (r)

71
Sternberg, (1966,1967)
72
Executive functions
  • Sequencing how is temporal order coded?
  • Sternberg, (1966, 1967)
  • note the large slope differences between the two
    tasks
  • Results suggest that different processes are
    involved item and order tasks one difficulty
    with experiment is that one task requires
    recognition while the other requires recall
    however, many studies are consistent with the
    idea that item and order information are stored
    and processed differently

73
Executive functions
  • Sequencing how is temporal order coded?
  • For example, there is evidence to suggest that
    memory for order information (information about
    associations) depends critically upon the
    hippocampus, but item information can be carried
    out independently of the hippocampus
  • There is also evidence indicating that sequential
    information can be stored and processed in a
    variety of ways

74
Executive functions
  • Sequencing how is temporal order coded?
  • There are many ways to code temporal order and
    there is evidence for each of these ways
    depending upon the task and other factors
  • 1. Associative e.g., X R C B L code as X
    precedes R R precedes C C precedes L etc.
  • 2. order tags e.g., X R C B L code as X is
    first R is second C is third, etc.
  • 3. familiarity e.g., a form of representation
    in which strength or familiarity of item is
    continuously represented, so more recent items
    are stronger than earlier items, allowing
    participants to make a judgement on that basis
    (e.g., B is stronger then C)

75
Executive functions
  • Sequencing related items
  • In many everyday situations, sequences of actions
    are related to each other, and in many cases have
    been performed several times in the past
  • E.g., eating out typically involves being
    greeted, taken to a table, ordering a meal,
    eating, getting a bill, paying, and leaving
    (Schank Abelson, 1977)
  • It is also possible to generate a novel script
    (e.g., opening a beauty salon)

76
Executive functions
  • Sequencing related items
  • Sirigu et al. (1985) performed an experiment in
    which patients with PFC damage, damage to the
    posterior cortex, and normal controls were tested
    on familiar and novel scripts
  • Participants were asked to generate familiar
    (going to a restaurant) and novel (opening a
    beauty salon) actions and then they were asked to
    order the actions into correct sequences

77
Executive functions
  • Sequencing related items
  • No significance difference in the number or type
    of actions generated
  • Individuals with PFC damage made more errors than
    other 2 groups when asked to order generated
    actions in correct sequence and the pattern was
    amplified with novel scripts
  • Similar findings were obtained when the different
    groups were given cards with actions for scripts
    written on them

78
Executive functions
  • Brain imaging studies
  • Buckner Wheeler (2001) reviewed findings from
    neuroimaging of remembering
  • Several studies have shown consistently with a
    variety of stimuli (words, faces, pictures) that
    during memory recall the dorsolateral prefrontal
    cortex and the anterior frontal-polar cortex are
    activated

79
Executive functions
  • Brain imaging studies
  • e.g., Buckner et al. (1995)
  • Participants studied a list of words (couple,
    string)
  • At test, during imaging, participants were shown
    the beginning of the word and were intstructed to
    recall the word (e.g., cou---, stri---- )
  • Results on next slide illustrate the pattern of
    activation

80
Buckner et al. (2001)
  • Typical pattern of activation during recall of
    studied material blue, dorsolateral (BA 44/6)
    green anterior frontal-polar (BA 10)

81
Buckner et al. (2001)
  • 2 brain regions appear to have distinct
    functional properties
  • Selectivity of anterior suggests it may have a
    specific memory function late onset consistent
    strategic retrieval/monitoring

82
Executive functions
  • Memory retrieval success
  • Evidence that MTL and PFC involved during memory
    retrieval, but are there additional regions?
  • Habib and Lepage (1999) meta-analysis
  • compared activation of old and new items
  • Results showed that a network consisting of left
    parietal cortex, left anterior frontal lobe (near
    frontal-polar region) responded more to old items
    (i.e., retrieval success)
  • This finding has been replicated in more recent
    studies with a variety of materials

83
Buckner et al. (2001)
  • Panel a. paradigm
  • Expt in which activation of old versus new items
    is compared

84
Buckner et al. (2001)
  • Panel b.
  • fMRI imaging show differential activation of
    brain regions associated with retrieval of
    success note left parietal cortex activation
    (green arrow)

85
Buckner et al. (2001)
  • Panel c.
  • Event-related potential (ERP) shows a rapid
    positive waveform that develops over left
    parietal sites during remembered old items (red)
    as compared to new items (green)

86
Executive functions
  • Spontaneous confabulations
  • Individuals, who spontaneously confabulate have
    also been used to investigate role of the frontal
    lobes and executive function in memory
  • Spontaeous confabulation statements are actions
    that reflect unintentional but obvious
    distortions of memory
  • honest lying
  • Spontaeous confabulation is found sometimes but
    not always after px who survive aneurysms of the
    anterior communicating artery (ACoA)

87
ACoA
  • Ventral view of arteries in brain
  • Damage to ACoA may result in memory loss,
    personality change and amnesia
  • Damage to ACoA often results in PFC damage

88
Executive functions
  • Spontaneous confabulations
  • Gilboa et al. (2006) investigated spontaneous
    confabulations
  • Participants were ACoA individuals who
    confabulate, ACoA individuals who do not
    confabulate, and controls

89
Executive functions
  • Spontaneous confabulations
  • Temporal context judgment experiment
  • In this experiment participants were required to
    make temporal context judgments about pictures of
    objects (Was this object presented earlier in
    this list i.e., not a previous list?)
  • Results
  • Not all ACoA patients were impaired on the
    temporal context confusion experiment, but those
    with ventromedial prefrontal cortex damage were
    impaired

90
Executive functions
  • Spontaneous confabulations
  • Familiar narratives experiment (fairy tales and
    bible stories)
  • In this experiment participants were asked to
    recall familiar narratives
  • Results spontaneous confabulators did not differ
    from ACoAs in terms of details recalled, but
    differed in terms of the number and type of
    errors (e.g., incorporation of details from other
    stories, idiosyncratic details)

91
Semantic narrative performance
  • Top mean details produced
  • Bottom proportion errors T total errors D
    distortions E external details (other
    stories) I idiosyncratic errors

92
Executive functions
  • Spontaneous confabulations
  • Further analyses
  • Only px with ventromedial prefrontal and
    orbitofrontal cortical damage were spontaneous
    confabulators

93
Executive functions
  • Spontaneous confabulations
  • Conclusion spontaneous confabulation does not
    appear to be a result of confusing true memories
    in time (evidence spontaneous confabulator
    errors such as semantic narrative external
    details)
  • instead it appears to be a difficulty of
    strategic retrieval and difficulties of
    monitoring
  • Strategic retrieval refers to a type of memory
    retrieval in which the target memory is not
    directly elicited by the retrieval cue (e.g.,
    what did you do on your birthday?), but appears
    to require problem solving

94
Executive functions
  • Spontaneous confabulations
  • Evidence for strategic retrieval
  • 1. Evidence from current study
  • 2. Finding that spontaneous confabulation is
    observed even for remote memories acquired prior
    to brain damage (when encoding of memories was
    intact) suggests stored memory is relatively
    intact and problem is in retrieval

95
Executive functions
  • Spontaneous confabulations
  • Gilboa et al. proposed
  • Strategic retrieval helps frame the memory
    problem and memory search
  • Constrains memory search
  • Once a memory is retrieved strategic retrieval
    monitors recovered memory for plausibility

96
Executive functions
97
Executive functions (social, personality and
emotional functions)
  • Overview
  • Gage walked away from accident, could describe
    the accident the next day, and within a month was
    deemed able to resume work as a foreman
  • It became clear that Gage was no longer Gage
  • Prior to injury Gage was a sober, responsible,
    intelligent, home body, with no peculiar or bad
    habits he was a responsible, valued employee
  • After injury he was erratic, given to grossest
    profanity, impatient, unwilling to listen to
    advice, and unable to plan effectively
  • Subsequent research has shown that damage to
    frontal lobes can lead to dramatic changes in
    personality while keeping perception,
    consciousness, and most cognitive functions
    intact
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