EXECUTIVE FUNCTIONS

EFs are multifaceted control processes that
regulate thought and behavior
A family of general-purpose mechanisms

Critical to other higher cognitive abilities
including planning, reasoning, long-term memory, decision making, and problem solving

Mediated mainly by prefrontal cortex, the parietal lobes, and subcortical regions, including the thalamus, basal ganglia, limbic system, mid-brain, and the cerebellum

Test used for EF
• Wisconsin card sorting test (WCST)
• N-back
• Trail making test B
• Stroop Task
• Stop signal
• AX-CPT

Miyake's model

  • inhibition
  • switching
  • updating
    They are related but independent

Working Memory

age related deficit in all of these factors

Complex tasks require that information are stored and
manipulated in a short-term storage system

Older adults have a reduction in WM storage capacity

This lead to deficits in several cognitive tasks but tasks that seem to tap into the function of WM capacity show minimal effect of age

it is not just the reduction in the storage capacity,
But rather an interaction of storage and control mechanisms

Age deficits in complex WM span tasks seem to mainly reflect a decline in executive control, rather than a decline in storage capacity

Executive deficit theories of cognitive aging
Goal manteinance deficit

  • Inhibitory Deficit Theory (Hasher & Zacks)
  • Frontal Lobe Hypothesis of Cognitive Aging
  • Goal Maintenance Deficit (Braver & West)

Goal Maintenance Deficit

  • deficits in executive control = which consists of the internal representation, maintenance, and updating of goal information in the service of exerting control over thoughts and behavior

executive control tasks rely on internal representations of tasks-set goals

  • Critical role of the lateral PFC in executive control processes
  • Critical role of the dopamine (DA) in executive control processes
  • DA modulates PFC function by regulating the way that goal representations are maintained and updated DA regulates the access of afferent inputs to lateral PFC

Lateral PFC:

  • exerts a top-down control on posterior and subcortical brain systems engaged in task-specific processing based on actively maintained goal representations
  • It's important in maintain in mind goals of the task and to transform goal representations into plan to respond to upcoming stimulus
  • required when multiple conflicting responses are activated but some are irrelevant

clarifies the relationship between attention, working memory and inhibition, and the role of lateral PFC in these domains: in situations of behavioral inhibition (stroop) top-down control may have a suppressive effect

Stroop

  • multiple perceptual dimensions that compete for attention
  • tendency to make an inappropriate response

Age-related declines in lateral PFC and dopamine function result in a specific impairment in the ability of older adults to actively represent and maintain goal information over time

Goal e Working memory

age effects on WM can be explained by the older adults’ reduced ability to maintain goal representations in working memory

  • Increased susceptibility to interference
  • declines in the ability to control the focus of attention within working memory
  • memory impairments occurring in task condition that require the binding of arbitrary stimulus features together in working memory

Susceptibility to interference

  • Proactive interf: previous stored info interfere with processing e tretrieval
  • Retroactive interf: interfering info is presented successively
  • minimizing proactive interference: better performance

Decline in the ability to control the focus of attention within working memory

  • short-term memory zone is very close to the conceptualization of actively maintaining goal representations within the goal maintenance account
  • O have a decline in refreshing and updating the focus of attention, in switching between the processing of no more relevant items and now relevant items

Binding deficit hypothesis

  • a disruption in the ability to bind together the various elements of a representation within working memory
  • memory tasks with retrieve of item based on a conjunction of more features show age-related deficit
  • Decline in left anterior hippocampus and right rostral prefrontal cortex

Inhibition of responses

  • inhibit irrelevant, inappropriate, but dominant or prepotent responses

Stroop task
This interference effect accelerates in an exponential fashion from the sixth to eighth decades

Antisaccade task
Difficulty in suppression of an automatic tendency to attentionally orient towards abrupt visual cues

Task management

difficulties in managing and coordinating multiple task demands

  • studies with task switching

no ages differences in SWITCHING COST
Only differences in MIXING COST

  • if there's a preparatory interval Y e O are facilitated but switching cost is greater in old

O unable to use info to appropriately select the current relevant task and deselect the irrilevant task

Lateral anterior PREFRONTAL CORTEX (PFC) plays a key role in maintaining task goals active in mind

  • in task switching blocks activation of Lateral PFC, which resulted associated with mixing costs
  • in O REDUCED activation of lateral PFC during task-switching blocks

Goal manteinance theory explain

  • WM
  • ep memory
  • prospective memory
  • inhibition of responses
  • task management

Paradigm AX-CPT:

  • Respond to an X following and A
  • errors in BX
  • errors in AY
  • O errors in BX, Y in AY
  • age related deficit in contextual info
  • in Y activation of lateral PFC: successful in BX inhibition but AY facilitation
  • impairment in the use of context info in O are caused by changes in lateral PFC

Temporal dynamic of Ex control

Dual mechanism of control DMC

  • proactive control = active manteinance of goal representation and anticipatory preparatory attention
  • reactive control = stimulus-driven reactivation of goal information in situation where such info is critical to avoid inappropriate performance

Older adults may have a reduced tendency to use proactive control, but a relatively spared or even enhanced tendency to engage in reactive control

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Ex control is more then a process
more areas:

  • left e right DLPFC activation,
  • inferior medial PFC monitoring,
  • superior medial PFC inhibition

Error/Performance monitoring

  • ERN error-related negativity: a specific ERP brain wave sensible to error monitoring and detection
  • electrophysiological signal associated with ACC monitoring process, occurring 100ms after an errors is made
  • activated not only for errors made, but also for response conflict
  • ACC provides a signal to PFC about the correction of behavior
  • It requires high degree of cognitive control
  • lateral PFC can adjust the actions based in ACC signals
  • amplitude of ERN is attenuated in O
  • reduction in the magnitude of dopamine-mediated error feedback signal from the basal ganglia to the anterior cingulate
  • DECLINE IN DOPAMINE ACC-PFC MONITORING SYSTEM

Somatic marker theory

  • Affective bodily signals can bias our decision
  • ventromedial regions of PFC
  • no age related effects in task used for vmPFC, aging effects on dlPFC
  • O show slower learning curves from negative feedback (errors) and higher tolerance to risk
  • O better control their emotions than Y and there's a reduced impact of negative info of memory and attention
  • even if vmPFC regions are not impaired, O show some deficits in affective-directed tasks due to deficit in dlPFC
  • Anterior PFC is involved in Ex processes related to integration of higher-order goal info actively maintained in WM
  • age differences in reasoning, high order thinking, planning, integration (aPFC dependent)