Executive Functions

Nathan Spreng

Cognitive Neuroscience: Psy393

August 8, 2005

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

Who is the Central Executive?

Lecture Outline

• PFC and overcoming the “default mode”

• Attributes of executive functions

• Goal Directed Behaviour

• Video

• Supervisory System

• Capgras case study

• Video (?)

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

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

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

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

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

Fuster J., 2003

Executive Functions

• Plan actions towards a goal

• Use information flexibly

• Realize consequences

• Draw inferences

• Independent of IQ

• 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

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

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

Executive functions

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

• Find a rule that can be used to group or sort disparate stimuli

• Shift attention to see the stimuli in a new way

Shifting & sorting tests -task demands-

• 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

Sorting tests – sub-processes

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

Wisconsin Card Sorting Test

Measures:

Categories, Perseverations, Loss of Set

Wisconsin Card Sorting Test• What frontal subregions are implicated?

– DLPFC: Milner (1963)

– Medial frontal: Drewe (1974)

– Orbitofrontal: Stuss et al. (1983)

• Posterior lesion effects

Wisconsin Card Sorting Test

• Is it sensitive and specific to frontal function in healthy adults?

WCST vs. sensorimotor control(Berman et al., 1995)

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

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).

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)

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

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

Cognitive flexibility and response to novelty

• FL deficits when...

– Learned behaviour must be overridden

– Environmental information doesn’t guide behaviour

Goal Directed Behaviours

• Staying on task

• Sequencing

• Shifting Set & Strategy Modification

• Using information to guide behaviour

• Self-monitoring

Staying on task

• Prerequisite for success

• FL patients wander off...

• DLPFC: maintenance of attention– establishes task relevancy

Sequencing

• Determining steps to achieve a goal

• Recognition v Recency– TL v FL

• Self-ordered pointing

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

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)

Shifting Set & Strategy Modification

(Dias et al, 1997; Slamecka, 1968; Owen, 1991)

• 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)

Shifting Set & Strategy Modification

(Dias et al, 1997; Slamecka, 1968; Owen, 1991)

• 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

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

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

• Video

Theoretical Account of Executive Functions

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)

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

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)

ContentionScheduling

(3)

TriggerDataBase

Special-purposeCognitiveSubsystems (1)

PerceptualSystem

SupervisoryAttentional System (4)

SchemaControl Units

(Action)

(2)

Supervisory Attentional System

Shallice (1981)

Four Components of the Supervisory System

1) Cognitive units or modules

2) Schemata

3) Contention scheduling

4) Supervisory (attentional) processes

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

Schema interactions

Seven Anterior AttentionCategories of Tasks

· Sustaining

· Concentrating

· Sharing

· Suppressing

· Switching

· Preparing

· Setting

Supervisory System

• Energize a Schema

• Inhibit a Schema

• Adjust Contention Scheduling

• Monitor Goal Fulfillment

• If-then Logic

E I C M L

Supervisory System

PerceptualInformation

EffectorSystem

E I C M L

Anterior Attention System

Schemata

Sustaining attention

• Definition:

• Attention to relevant events occurring at a relatively slow rate over prolonged periods of time

a b c c

E I C M L

Sustaining Attention

a. Energize task schema

b. Inhibit competing schema

c. Monitor responses on and off tasks

Concentrating Attention

• Definition

• Attention when task is demanding and relevant events occur too quickly rather than too slowly

Concentrating Attention

a. energize task schema b. decrease inhibition among similar schema to allow high activity levels in several schema c. monitor responses on tasks for minutesd. If-then logic

E I C M L

a b cd

d

Fractionating the SAS

Process Goal Putative localization

Sustain Mitigate schema decay R Frontal

Concentrate Activate one schema, inhibit others Anterior cingulate

Sharing Activate two schemas Orbitofrontal, ACG

Suppress Inhibit selection of inappropriate schema

DLPFC (L?)

Switch Activate recently inhibited schema DLPFC, medial PFC

Prepare Submaximal activation for later response

DLPFC

Set Consistent mobilization of most appropriate schema across sessions

L DLPFC

Stuss et al. (1995)

Capgras Syndrome

Misidentification of people as other people, or locations as other locations

(Stuss & Alenxander, 1979;1999)

Reduplicative Paramnesia: Subjective certainty that a familiar place or person

has been duplicated

Capgras Syndrome

• CT

• Diminished density– Bilateral frontal

– Right temporal (including amygdala)

• Enlarged ventricles – (R > L)

• Significant cognitive impairment, including executive functioning and memory;

• Slow recovery10 months after injury: first weekend visit

wife - new hair cut, new carteenage kids - a year older

Capgras Syndrome

• Reports disorientation

• New family has replaced the old– with notable similarity

• Desertion of previous wife not distressing– kind enough to find replacement

Capgras Syndrome

Demonstrates implausibility but cannot change feeling

Capgras Syndrome

• Years later:– Maintained belief of second family– Neuropsychological testing: normal IQ,

memory, language, basic attention; impaired on “frontal tests”

• Why?– Executive functioning impairment

• Failure of personal evaluation or validation of the situation