Executive Functions

1. Executive Functions Nathan Spreng Cognitive Neuroscience: Psy393 August 8, 2005

2. Preliminary issues • Lecture slides & email • Last exam • Paper – download problems? • www.library.utoronto.ca/resources • Final Exam: Tuesday August 16, 2-5pm • Room: SF 3202 • Basic frontal lobe neuroanatomy

3. Who is the Central Executive?

4. Lecture Outline • PFC and overcoming the “default mode” • Attributes of executive functions • Goal Directed Behaviour • Video • Supervisory System • Capgras case study • Video (?)

5. Default mode • Default mode: • inflexible stimulus-response linkages • promotes automatic reactions and immediate gratification • sensitive predominantly to the internal milieu • remains resistant to modification by context or experience • Preference for sameness and certainty • Which promotes stimulus bound or stereotyped behaviour • Ego-centric, here-now perspective. • More conspicuous in sub-mammalian species, children, FL patients • Remains in latent form for healthy normals

6. Default mode • The principle physiological function of the PFC is to suppress and transcend the default mode • introducing circuitry where neuronal responses can become contingent rather than obligatory • Stimulus - Response: • one-to-one relationship • One-to-many response options afforded by the PFC, tolerates greater uncertainty, diversity and choice

7. Frontal Lobes • Four core functions: • Working memory & attention • Inhibition of distraction, perseveration, and immediate gratification • Ability to encode context and perspective • Dynamic mapping of significance

8. Executive Function: Attention • Enables on-line holding of information. • Incorporates info into a stream of consciousness • Maintenance of convergent information from different modalities • Shifting attention from external events to their internal representations • On-line manipulation of information • important role in the voluntary scanning and reorganization of mental content • Enables one to transcend stimulus bound thought that is reflexive and environmentally based towards a selective and deliberate consciousness

9. Executive Function: Future Perspective • PFC mediates shifts in time so that intended actions and their consequences can be apprehended from the vantage point of the future. • PFC neurons in monkeys fire in anticipation of reward (Hikosaka and Watanabe, 2000) • PFC activation in estimation of temporal intervals in humans (Coull and Nobre, 1998) • shifting awareness to the inferred future • Enables the prediction of consequences for contemplated behaviours, essential for planning, sequencing and foresight • -impaired in PFC damage

10. Fuster J., 2003

11. Executive Functions • Plan actions towards a goal • Use information flexibly • Realize consequences • Draw inferences • Independent of IQ

12. Frontal lobe damage produce deficits in: • Initiation, cessation and control of action • Abstract and conceptual thinking • Cognitive estimation and prediction • Cognitive flexibility and response to novelty • Goal directed Behaviours

13. Initiation, Cessation & Control of Action • “Psychological Inertia” (Luria, 1966) • Spontaneity and Fluency loss • Perseveration: repetitive behaviour unresponsive to feedback or reward • Environmental dependency syndrome (Lhermitte, 1983) • Separation of knowledge and actions

14. Psychological Inertia • Tasks assess ease and fluidity of concept generation • Verbal Fluency: words starting with “s” • L-PFC sensitivity • repetitions, halting speech • Non-verbal Fluency: figures with 4 straight lines • R-PFC sensitivity

15. Executive functions • Shifting concepts • Part-whole relations • Integrating isolated ideas • Handling simultaneous sources of information • Use of feedback • Translation of knowledge to action

16. Shifting & sorting tests -task demands- • Find a rule that can be used to group or sort disparate stimuli • Shift attention to see the stimuli in a new way

17. Sorting tests – sub-processes • Identification and generation of concepts • Hypothesis testing • Maintenance of attention • Resistance to interference • Utilization of feedback to guide behavior • Inhibition of perseveration • Shifting of cognitive set • Perceptual, motor processes

18. Wisconsin Card Sorting Test(Grant & Berg, 1948; Milner, 1963) • Wisconsin Card Sorting Task (WCST) • no explicit rules • learn from feedback • must shift to new contingencies (10 correct) • Test characteristics • Administration methods • Nelson, 1976:"Having failed to grasp the test requirements, bewilderment frequently turns to distress as responses are negatively reinforced on a basis that to the patient appears totally arbitrary (if not perverse)." • Measures • Categories, Perseverations, Loss of Set

19. Wisconsin Card Sorting Test • Measures: • Categories, Perseverations, Loss of Set

20. Wisconsin Card Sorting Test • What frontal subregions are implicated? • DLPFC: Milner (1963) • Medial frontal: Drewe (1974) • Orbitofrontal: Stuss et al. (1983) • Posterior lesion effects

21. Wisconsin Card Sorting Test • Is it sensitive and specific to frontal function in healthy adults? WCST vs. sensorimotor control (Berman et al., 1995)

22. Wisconsin Card Sorting Test • Sensitive to diffuse injury and certain posterior damage • With proper controls • Perseveration sensitive to DLPFC and superior medial frontal damage • Set loss sensitive to inferior medial and right DLPFC damage • Task sensitivity modulated by examiner-provided structure • Not a proxy for frontal function in healthy participants

23. Psychological Inertia • Environmental dependency syndrome (Lhermitte) • Utilization behavior • Actions impelled by the physical or social environment • Excessive dependency on the immediate environment • stereotyped responses • ignoring context. • Interferes with behavioural flexibility and individual autonomy (free will).

24. Neuroimaging • Go/No Go • go trial: push button • no-go: withhold response (more difficult if rare) • fMRI • R-DLPFC (BA46/9) • R-VLPFC (BA44) • Anterior Cingulate (ACC)

25. Abstract v Concrete Thinking • Modified WCST • Conceptual sorting criteria • 2 groups, 8 dimensions • water/land, triangle location, etc. • 2 groups, 8 dimensions Conceptual sorting criteria • Deficit in sorting into meaningful piles even with concrete clues

26. Cognitive Estimation & Prediction • Cognitive estimation deficits: deducing judgment from known information • Prices • Time to complete • Prioritizing becomes difficult • Intact knowledge base (Semantic memory) • Prediction impaired for social and ToM

27. Cognitive flexibility and response to novelty • FL deficits when... • Learned behaviour must be overridden • Environmental information doesn’t guide behaviour

28. Goal Directed Behaviours • Staying on task • Sequencing • Shifting Set & Strategy Modification • Using information to guide behaviour • Self-monitoring

29. Staying on task • Prerequisite for success • FL patients wander off... • DLPFC: maintenance of attention • establishes task relevancy

30. Sequencing • Determining steps to achieve a goal • Recognition v Recency • TL v FL • Self-ordered pointing

31. Sequencing • Tower of London (Shallice, 1982) • Move balls one at a time • Desired position • Minimum moves • FL lesions, L > R deficit. Aimless moves • Neuroimaging: DLPFC, L > R activity

32. Shifting Set & Strategy Modification • Conceptual or perceptual shift deficits • Changing directions midway through • sorting task • Switching: FL region determined by task demand • Involves inhibition of previous set • Formation of new set (Dias et al, 1997; Slamecka, 1968; Owen, 1991)

33. Shifting Set & Strategy Modification • A Respond according to shape • B Respond according to shape • Shapes replaced with novel exemplars • Intradimentional • C Shift to other dimension (lines) • Previously relevant dimension must be present to evoke deficits • D Reversal of reward contingencies (within dimension) (Dias et al, 1997; Slamecka, 1968; Owen, 1991)

34. Shifting Set & Strategy Modification • L-PFC shifts attention between perceptual dimensions • OFC reverses stimulus-reward associations within perceptual domains • Mechanisms of on-line processing are independent of inhibitory control in PFC • Impairment of inhibitory control is restricted to novel situations • PFC areas involved in • suppression of previously established response sets • not involved in the acquisition of these response sets (Dias et al, 1997; Slamecka, 1968; Owen, 1991)

35. Guiding behaviour • Environmental contingencies influence effective goal directed behaviour • ex: Telephone call while making dinner • Sub-goals interwoven • Neuroimaging hierarchical subgoals: OFC • 2 tasks performed in succession towards a general goal • baseline: task switch no retention • and holding info over delay

36. Self-monitoring • Is the goal being approached? • Diminished motivation • Error monitoring involved? (ACC) • error detecting • conflict monitoring • FL works with the ACC to monitor action and subjective (not absolute) detection of errors

37. Video

38. Theoretical Account of Executive Functions

39. Theoretical accounts • Feedback utilization (Luria) • Inhibition (Dias, 1996; Diamond, 1989) • Working memory (Goldman-Rakic, 1987; Kimberg & Farah, 1993) • Scripts & “managerial knowledge units” (MKU; Grafman, 1989) • Supervisory Attention (Norman & Shallice, 1986; Stuss et al, 1995)

40. Controlled vs. Automatic Processing • Contention Scheduling • automatic processing • time & learning • role of FL diminishes with experience • Supervisory Attention System • effortful/controlled processing • where automatic processing would fail and must be overcome • novel events without processing schemes • when tasks are technically difficult • problem solving required

41. Supervisory Attention System • Modules: Basic cognitive operations • Schemata: Standard and routine programs for the control of overlearned skills in the modules • Contention Scheduling: The lateral inhibitory mechanisms that control competition between schemata • Supervisory System: General executive • Situations where incorrect response is liable to be produced by unmodulated contention scheduling • Situations in which no routine exists (novel). Shallice (1982); Norman & Shallice (1980)

42. Supervisory Attentional System Supervisory Attentional System (4) Schema Control Units Trigger Data Base Contention Scheduling (3) Perceptual System (2) Special-purpose Cognitive Subsystems (1) (Action) Shallice (1981)

43. Four Components of the Supervisory System 1) Cognitive units or modules 2) Schemata 3) Contention scheduling 4) Supervisory (attentional) processes

44. Four Components of the Supervisory System 1) Modules: Basic cognitive operations 2) Schemata: Standard and routine programs for the control of overlearned skills in the modules 3) Contention Scheduling: The lateral inhibitory mechanisms that control competition between schemata 4) Supervisory System: General executive component - top down processing

45. Schema interactions

46. Seven Anterior AttentionCategories of Tasks • Sustaining • Concentrating • Sharing • Suppressing • Switching • Preparing • Setting

47. Supervisory System • Energize a Schema • Inhibit a Schema • Adjust Contention Scheduling • Monitor Goal Fulfillment • If-then Logic E I C M L

48. Anterior Attention System Supervisory System E I C M L Schemata Perceptual Information Effector System

49. Sustaining attention • Definition: • Attention to relevant events occurring at a relatively slow rate over prolonged periods of time

50. Sustaining Attention a. Energize task schema b. Inhibit competing schema c. Monitor responses on and off tasks E I C M L a b c c