Lecture 3: Part 2:

Executive control and the prefrontal cortex:

Executive functions:

• Executive functions give organisations and order to our actions and behaviour.

• Govern a number of different domains (cognitive, linguistic, motor) and involve pre-frontal and subcortical loops.

• Includes:

  • Representing and maintaining goals

  • Planning for the future

  • Inhibiting or delaying responding

  • Initiating behaviour

  • Shifting between activities flexibly.

The prefrontal cortex:

• Dorsolateral

• Ventrolateral

• Anterior pole

• Ventromedial

3 characteristics of PFC neuroanatomy:

• Late phylogenesis (evolutionary history)

• Late ontogenesis (developmental history)

• Highly interconnected with virtually all other brain areas (bilaterally)

PFC damage:

• Dorsolateral lesions lead to frontal executive syndrome.

• Constellation of problems in planning, flexibility adapting to new situations, withdrawal from social situations.

• Ventromedial damage can lead to problems with emotional control.

PFC and working memory:

• Dorsolateral PFC lesions lead to stimulus-driven behaviour.

• Disrupts alternation task in humans and monkeys

• Perseveration: Repetition of response.

Wisconsin card sorting task in humans:

• Sorting rule changed during task

• Learning rule requires WM.

• Lateral PFC patients perseverate with old rule.

• Sustained DLPFC activation over delay period in working memory tasks with fMRI.

• Greater activity with greater WM demand.

Goal oriented behaviour:

• Patients with frontal brain damage have problems with everyday life.

• Planning involves creating a hierarchy of goals and sub-goals.

• Patients fixate on certain aspects and fail to consider others.

• Individuals first taught to respond to one of two black shapes and to ignore the white shapes. (A)

• Intradimensional shift - discriminate between two new black shapes (B)

• Extradimensional shift - discriminate between two white shapes (C)

• Greater deficit apparent in extradimensional shift.

Staying on track:

• How are interactions between frontally-mediated WM systems and posterior processing areas governed?

• As task difficulty increases, the Anterior Cingulate (AC) gyrus becomes increasingly active

• The AC is involved in monitoring the environment, one‘s behaviour, and the relationship between the two

• This keeps behaviour on track (goal directed)

• The Error-Related Negativity (ERN)

Detecting errors: The error related negativity:

• A negative component thought to be generated in AC

• Occurs following error decisions

• May aid learning

Avoiding errors:

• Avoiding errors – AC activation is greater when people do tasks that elicit errors, such as the hard condition of the Stroop task, or with incompatible flankers

• Inhibiting habitual responses

Impulse control:

• Phineas Gage had problems with impulsive decisions

• He also had problems with inappropriate emotions

• These two aspects of mental life may be related and dependent on overlapping neural substrates

• Antonio Damasio‘s somatic marker hypothesis

• Bodily sensations act as a heuristic guide to making decisions

• Emotions involve bodily sensations

• Ventromedial frontal cortex is involved in emotions

vmPFC damage:

• Lesions to vmPFC often result in:

• Reduced inhibition of affect – rude and hostile

• Deficits in reversal learning

• Impaired reward expectation/prediction – impaired long-term planning

• Impaired at maintaining a job and healthy social relationships despite their spared intellectual and mnemonic functions.

Making good decisions:

• Emotion is important:

• VM patients lack skin-conductance response to emotive stimuli

• Fail to learn aversion to a risky decision – Iowa Gambling task

Summary:

Executive Functions involve

• inhibition

• planning

• working memory

• self-monitoring

• response selection

• motor control

• regulation of emotion

• motivation