Executive processes

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

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)

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, Broca’s area, and the medial and orbital regions of the frontal lobes

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

Executive functions

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

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

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

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

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

Executive processes • Working memory and lateral prefrontal cortex • A previous lecture discuss working memory • Baddeley’s model of working memory was presented

Baddeley’s working memory model Visuo-spatial sketchpad Phonological loop Central Executive

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

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

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

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

Executive processes • D’Esposito et al. (1998) • Meta-analysis • D’Esposito 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

Executive processes • D’Esposito 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 D’Esposito categorized studies based on their content (spatial, nonspatial)

Executive processes • D’Esposito et al. (1998) • Results partially 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, but not • However, there was bilateral activation in many studies • See top panel

D’Esposito et al. (1998) • Top panel shows active foci for spatial and nonspatial tasks (content) • Bottom panel shows active foci for maintenance and maintenance + tasks

Executive processes • D’Esposito 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

D’Esposito et al. (1998) • Top panel shows active foci for spatial and nonspatial tasks (content) • Bottom panel shows active foci for maintenance and maintenance + tasks

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

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

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

Stroop (slide 2) • redyellowblue red • greenred yellow green • blue green redyellow • red green redyellow

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

Stroop (slide 3)

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

Executive functions 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

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

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)

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”

Executive functions

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

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

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

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

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

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

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)

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

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

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

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

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

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)

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

Executive processes