Lec 4 Executive function and executive dysfunction Flashcards
1. to understand that different diseases, with different mechanisms can share the same symptom, e.g., executive dysfunction in ADHD and frontal lobe syndrome 2. to appreciate the blurred line between 'treatment' and 'enhancement', given that transient executive dysfunctuion can occur inthe healthy brain (i.e., under sleep deprivation or stress)
Definition of executive function
inhibit inappropriate behaviour
visual imagery (foresight, hindsight, a sense of time)
verbal working memory (talk to oneself in one’s mind)
control emotions
plan and problem solve
what is the difference between intelligence and executive function
executive dysfunction is an impairment in major life activities despite normal IQ
One study used 149 adults (19-25yrs) diagnostic with ADHD during childhood and 79 community controls, and followed up for 13 years, and controlled for age, duration of follow up and IQ matched or statistically controlled. They used interview, employers questionnaire (anonymized) and schoold records,
they found that impairment insocial life in ADHD with IQ regressed out, teenage pregnancies 38% ADHD vs. 4% controls, fewer friends more trouble keeping friends and more social problems as rated by parents in ADHD group
what are the symptoms of executive dysfunction
Core symptom: AHDH, Frontal lobe lesion
Additional symptom: schizophrenia, depression, dementia, basal ganglia lesion/ Parkinson Disease
Can also occur transiently in healthy people, i.e., if sleep deprived or stressed out
Clinical view of executive dysfunction
a mismatch btw a relatively preserved IQ and a profound fisability at real life tasks such as holding employment or maintaining social relationships
disinhibited/ inappropriate behaviour
inability to maintain goals and to plan
emotion dysregulation
lack of flexibility (apathy, perseveration)
the cognitive psychology view of the executive function
a family of top-down mental processes needed when you have to concentrate and pay attention, when going on automatic or relying on instinct or intuition would be ill-advised, insufficient or impossible
inhibition
working memory
flexibility
what neuropsychological tests can be applied to executive function?
Stroop test: report ink color
Wisconsin Card Sorting Test (WCST)
Participants see piles of cards with different characteristics. they are asked to sort each card into the piles based on their similarity. the rules of sorting cards are changing between ‘same background’, ‘same shapes’, and ‘same number’. You must infer what rule is active based on the feedback you get. If your response is correct you know what rule is active.
Fluency test
generate as many words as possible beginning with one letter, typically ‘B’, ‘F’, ‘A’, ‘S’, ‘T’ in 2 minutes
what are the similarities of neuropsychological tests used to test executive function
Stroop, WCST, fluency task all inhibit inappropriate response. Both WCST and fluency task test working memory and flexibility
what are the limitations of neuropsychological tests used to test executive function
Do these tests predict other aspects of executive function, i.e., emotion regulation?
Do these tests predict the patient’s impairment in real life?
Low scores in brain lesion patients due to other impairments independent of executive function (EF) (i.e., visual acuity or intelligence or memory)
Are the tests tapping into similar or different cognitive components?
what are the brain mechanism that support executive function
1) structural damage of prefrontal cortex
executive dysfunction occurs after a lesion in the prefrontal cortex
a) prefrontal cortex is not special due to its size. Although human frontal lobes are largest in terms of volume compare to other species, the relative size compared to the other parts of the brain is the same as it is in other animals,
b) human frontal cortex helps mediate working memory.
however, frontal lobe is the only structure that is active during working memory task. parietal cortex is also active. however, a lesion in parietal cortext doesnt leads to executive dysfunction. hence working memory could not be the only side of the story
c) frontal cortex is shown to be very flexible
one fMRI study record healthy subjects brain activation time series (e.g., from one voxel with all other voxels in the brain), brain connectivity can be understand as correlation.
the frontal cortex is indeed very correlatied and flexible, but it is not the only highly correlated, parietal cortex (which also mediates working memory), is flexible, too.
d) the flexibility of frontal cortex is also seen in measureof single prefrontal cortex cells. single cell recording on monkey who trained to perform category differentiation tasks showed that same neuron could respond differently to cats and dogs. it showed distinct firing for stimuli of one category versus the other and responded to the category membership of the stimuli.
2) Pharmacological imbalance of dopamine system or norepinephrine
the system that are thought to be connected to excutive function are dopamine and norepinephrine system
key structure of dopamine system is substantia nigra, from there project to basal ganglia, striatun, thalamus, and then to frontal cortex and other associated area
key structure of norepinephrine system are the tegmental fields and locus ceruleus, from there projection to thalamus–>limbic system–>frontal cortex–>other association area and cerebellum
prefrontal cortex shows persisten firing during the delay period if the cue had occured at the preferred direction for this neuron (oculomotor delayed response task).
Neurotransmitters are found to modulate the neurons in the receptive field. Catecholamine influences on PFC physiology and function.
Both NE and dopamine have inverted U-shaped influences on PFC physiology and cognition, whereby either too little or too much of the neurotransmitter impairs PFC function.
atomoxetine, a selective norepinephrine reuptake inhibitor (ADHD treatment) show similar pattern
How effective are the rehabilitation strategies of executive dysfunction
In adults: cognitive rehabilitation involving training of working memory, compensatory strategies or independence wih daily living, measured global EF, working memory, ADL, quality of life, participation in vocational activity. no evidence for an effect of cognitive rehabilitation of executive dysfunction in adults with brain lesion
In children:cognitive training, sports-aerobics, yoga, tae-kwon-do, pretend play, few studies and poorly investigated, training helps most in kids with lowest executive function score, effects do not transfer between executive functions (i.e. working memory training does not help inhibition
what are the factors that worsen executive function in healthy population
academic stress; reversibly; sleep deprivation; not being physically fit; exerting self-control
Does self-control resemble a muscle?
one expt looked into consecutive act of self-control in the form of resisting temptation.
manipulated self-control by instructing some hungry individuals to eat onl radishes while they were faced with the tempting sight and aroma of chocolate. thus, they had to resist the temptation to perform one action while making themselves perform a similar but much less desirable action.
we then thought to measure self-control in an unrelated spere, b persistence at a frustrating puzzle-solving task. A series of frustrating failures may often make people want to stop doing the task, and , so, self-control is needed to force oneself to continue working.
Result: people who forced themselves to eat radishes instead of tempting chocolates subsequently quit faster on unsolvable puzzles than people who had not exert self-control over eating
this is an evidence of ego depletion. resisting temptation seems to have produced a psychic cost, in the sense that afterward participants were more inclined to give up easily in the face of frustration.
an initial act of resisting temptation (i.e. an act of impulse control) impaired subsequent persistence at a spatial puzzle task
this suggest that the self’s capacity for active cvolition is limited and that a range of seemingly differenet, unrelated acts share a common resource
effect of cognitive enhancement in healthy population
Metaanalysis on Ritalin (288 studies): single dose showed significant improvement in memory, no significant effect on executive function. In sleep deprived individuals: over-estimating performance
Metaanalysis on Modafinil -130 studies
single dose lieads to significant improvement in attention and wakefulness, in sleep deprived individuals: significant improvement of executive function
