The Executive Brain

The executive brain.

Progress Njomboro

Phineas Gage (1823-1860)

Temperate habits

Considerable energy of character

Well balanced mind

Shrewd, smart, and persistent

A horrible accident!
Phineas Gage (1823-1860)

Gage was a respected and hard working foreman of a crew of railroad construction workers who were excavating rocks to make way for the railroad track. This involved drilling holes deep into the boulders and filling them with dynamite. A fuse was then inserted, and the entrance to the hole plugged with sand, so that the force of the explosion would be directed into the boulder. This was done with a crow bar-like tool called a tamping iron.

On 13th September, 1848, 25-year-old Gage and his crew were working on the Rutland and Burlington Railroad near Cavendish in Vermont. Gage was preparing for an explosion by compacting a bore with explosive powder using a tamping iron. While he was doing this, a spark from the tamping iron ignited the powder, causing the iron to be propelled at high speed straight through Gage’s skull. It entered under the left cheek bone and exited through the top of the head, and was later recovered some 30 yards from the site of the accident.

Whether or not Gage lost consciousness is not known, but, remarkably, he was conscious and able to walk within minutes of the accident. He was then seated in an oxcart, on which he was transported three-quarters of a mile to the boarding house where he was staying. Here, he was attended to by Harlow, the local physician. At the boarding house, Harlow cleaned Gage’s wounds by removing small fragments of bone, and replaced some of the larger skull fragments that remained attached but had been displaced by the tamping iron. He then closed the larger wound at the top of Gauge’s head with adhesive straps, and covered the opening with a wet compress. Gage’s wounds were not treated surgically, but were instead left open to drain into the dressings.

Phineas Gage (1823-1860)

Harlow, Gage’s physician, describes how Gage regained his strength and how his physical recovery was complete.

‘He could touch, hear, and see, and was not paralysed of limb or tongue. He walked firmly, used his hands with dexterity, and had no noticeable difficulty with speech or language.

And yet, the ‘equilibrium or balance, so to speak, between his intellectual faculty and animal propensities’ had been destroyed.

Phineas Gage (1823-1860)

‘He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint of advice when it conflicts with his desires, at times pertinaciously obstinent, yet capricious and vacillating, devising many plans of future operation, which are no sooner arranged than they are abandoned in turn for others appearing more feasible’.

To his friends and work mates, he was “no longer Gage”  

Gage’s brain.

Hanna Damasio & Thomas Grabowski

Motor  & premotor cortices, Broca’s area spared.

VMPC among the damaged areas.

Objectives

Describe executive processes

Outline the neurological substrates of executive functions,

Review the neuroanatomical features  of the prefrontal cortex and the Anterior Cingulate Cortex

Evaluate some cognitive models of executive functions.

Discuss clinical profiles of executive function deficits.

Executive Functions (EF)

They are processes responsible for the cognitive control of goal-directed behavior.

Instructs other areas of the brain to perform, or remain silent...

Executive Functions (EF)

They are processes responsible for the cognitive control of goal-directed behavior.

Components

Volition

Planning

Purposive action

Affective performance

Executive Functions (EF)

Monitoring

Sequencing

Planning

Decision making

Error correction

Trouble shooting

Dealing with novelty

Response suppression / inhibition

Response initiation

Mental set shifting/ switching

For instance.....

An executive system is able to:

focus attention against potentially distracting irrelevant information

Switch attention between two or more stimulus sources or actions

Divide attention in order to perform two concomitant tasks

Interface with long term memory

                                               (Baddeley, 1996)

Executive Functions (EF)

 Enables self-regulation, problem-solving and goal directed behaviour.

They are necessary for adaptive, appropriate, socially responsible, self-serving adult conduct.

Domain specific

top down vs bottom-up processes

The frontal lobe link.

Frontal lobotomy

The frontal lobe link.

The frontal lobe link.

Functional divisions of the PFC.

Lateral

Medial

Orbital (VMPC)

Hemispheric specialization in the PFC

Dorsolateral PFC

Left - response selection

Right – monitoring

Ventrolateral PFC – maintenance

Left – word processing (Wagner et al., 1998)

Right- spatial working memory (Manoach et al., 2004)

Inhibition (Aron et al., 2004)

Anterior PFC- multi-tasking.

The Anterior Cingulate cortex (ACC)

Response conflict (stroop)

Drive/ motivation

Error detection

The Frontal lobes and Intelligence

Most frontal lobe Patients do well on IQ tests than patients with lesions elsewhere.

Unless the tests tape into Efs (e.g. situations of novelty, requiring flexible thinking and problem solving).

Social intelligence (cooperation, empathy, deception, etc) which is not tapped by most IQ tests - appears to be dependent on the integrity of the PFC.

Are EF limited to the prefrontal cortex?

Frontal sub-cortical circuits link the frontal lobes with other areas of the brain

Disconnection between the PF and areas for various cognitive processes, (eg., language) may cause dysexecutive symptoms within that respective process.

Executive deficits become apparent when the

environment contains distracters, ambiguity

and conflict are high, appearance and

significance are at odds, events must be

interpreted in light of contextual peculiarities,

prepotent response tendencies must be

restrained for long-term purposes, decision

trees have multiple branches, and an

egocentric point of view must be transcended.

                                                                                (Stuss & Knight 2002)

Measurement and Assessment of EF.

Where are they recruited?

Situations involving :

Planning and decision making

Error correction or trouble-shooting

Novelty or response that are not well learnt

Danger or difficulty

Need to over-come strong habitual response

Planning and decision making

    Tower of Hanoi

Patients must move disks from one stake to another to reach a specified end-point

Planning and decision making

   The Multiple Errand test

Requires the patient to multi-task in a shopping precinct (e.g. finding the price of tomatoes, being in a certain place 15 minutes after starting)

Error Correction and trouble-shootingWisconsin card Sorting test

Color

Shape

number

Error Correction and trouble-shooting

Novelty

Cognitive Estimates test

How many camels are in Holland?

How many seeds are there in a water melon?

How many brushings can one get from a large tube of tooth paste

How long is a table spoon

Novelty

FAS test 

participants must generate a sequence of words (not proper nouns) beginning with a specified letter in a 1-minute period.

Eg., F, A, and S.

Difficult situations

Wilkins, Shallice and McCarthy (1987) - easy and difficult tasks (sustained attention) involving the counting of clicks.

Patients with lesions to the PFC (particularly on the right) were impaired on the difficult but not easy task

Risky/Dangerous situations

Situations of danger and risk are likely to involve affective, reward/punishment processing.

Ventromedial and orbitofrontal cortex implicated in this aspect of EF

Response suppression/conflict

                The Stroop Test

Response suppressionThe Hayling Sentence Completion Task

Assessment problems

Task impurity problem (Burgess, 1997; Phillips,1997).

Tests engage multiple cognitive processes.

The tasks are complex and poor performance on them could arise for many different reasons.

deficits are therefore difficult to interpret.

Assessment problems

People can adopt different strategies on different occasions (or even within a session) when performing these tasks…

Repeated encounters with the task reduces its effectiveness in capturing the target executive process…

..so executive tasks suffer from relatively low internal and/or test–retest reliability

Assessment problems

their construct validities are not well established (Phillips, 1997; Rabbitt, 1997b; Reitan & Wolfson,1994).

Eg.,

The WCST, has been suggested by different researchers as a measure of ‘‘mental set shifting,’’ ‘‘inhibition,’’ ‘‘flexibility,’’ ‘‘problem solving,’’ and ‘‘categorization’.

Assessment issues

Patients with clear real life dysexecutive symptoms sometimes do well on these tests:

Probably because instructions and feedback  give participants some structure that is absent in real-life goal directed activity.

Models of Executive function

EF models focus on how executive functions are organized and what roles they play in complex cognition.

They also try to answer some basic questions in the area. For instance;

How functionally and neurologically separable are Efs like shifting of mental sets, monitoring and updating of working memory representations, and inhibition of prepotent responses.

Unitary Models of Executive Functions

Evidence of correlation between EF tests a common basis or a unifying mechanism across Efs

Goal maintenance (e.g. Duncan)

Goal neglect produces EF deficits.

Associative networks (Kimberg & Farah)

Competition (and weakening associations) across the network leads to some tasks being prioritised over others

In support of these models, literature suggest individual EFs are hard to localize.

Goldman-Rakic’s Working Memory Model (1992, 1996)

PFC updates( (monitors) information stored in posterior regions of the brain.

VLPFC – working memory for objects

DLPFC – spatial working memory

Petrides’ model of maintenance vs. manipulation.

Supervisory Attentional System Model
 Norman & Shallice, 1986; Shallice & Burgess, 1996

Controlled behavior arises through selection of schemas that comprise stored action and problem-solving routines.

eg., Schemas can be triggered:

•          by stimuli or individual goals

•          By the outcome of a problem-solving phase

•          by a prior intention

•          Contention scheduling selects an adaptive schema

•          The 1996 SAS model contains separate Efs for implementing the schema, and monitoring and checking its appropriateness in terms of behavioral outcomes.

Miller & Cohen’s integrative model

The PF maintains goals and rules

that help create maps between sensory inputs, internal states, and response outputs

There may be differences in how appetitive and socio-emotional processes are regulated compared to more cognitive processes.

The PF is involved in both working and prospective memory

Fractionating the Executive?

Clinical observations indicate some dissociations in performance among the executive tasks, suggesting that executive functions may not be completely unitary

Intercorrelations among different executive tasks are low.

Factor analysis studies show Efs tend to yield multiple separable factors (rather than a single unitary factor) for a battery of executive tasks.

BUT: It is quite possible that differences in nonexecutive processing requirements (e.g., language and visuospatial processing) mask the existence of some underlying commonalities among executive tasks.

Functional specialisation within the lateral prefrontal cortex

If EFs consist of distinct processes, its possible they also have distinct neural substrates.

Brain imaging and lesion studies suggest some degree of PF functional specialisation

Specialization may also be a result of different PF areas connecting to different areas of the brain.

Response selection: L/DLPFC

Activated in ‘free choice’ and ‘free word generation’ PET tasks (eg., Frith et al., 1992)

Also active when participants select when to make a response

TMS over the L/DLPFC gives less random and more familiar sequences on random digit generation tasks

Monitoring : R/DLPFC

Checking and Relating infor back to task requirements

eg., working memory, sustained attention in conditions of uncertainty

Activated under complex N back and rule induction tasks

Maintenance: VLPFC

Maintenance of infor in working memory

Activate stored knowledge

Refreshing/ rehearsal mechanisms to sustain posterior brain activity

L/VLPFC: words memorisation

R/VLPFC: Unfamiliar faces/ inhibition

Multi-tasking: Anterior PFC.

Carrying out several tasks in succession is thought to involve the anterior PFC

(Also called the rostral PFC or frontal pole)

Activated when participants hold a main goal in mind while concurrently performing other subgoals.

The ACC

An interface between the limbic and frontal lobes.

Dorsal ACC region: cognitive/excutive  division

Error monitoring

Response conflict (stroop)

Evaluation of response?

Rostral ACC region : affective division

Task switching

Discarding a previous schema and establishing a new one incurs a ‘switch cost’.

Task switching

Task switching

Task switching

Task switching

Task switching

Rogers & Monsell, 1995’s task produced a switch cost

What produces the switch cost?

Retrieval of alternative schema from memory

Automatic trigger of old schema

Interference from an old schema that’s compatible with the new schema

Suppressing old schema

Setting up new one

Conclusion

E
N
D