What is the Mesulam mystery?
- Clinicians working with neurological patients were noticing that often frontal lobe lesions did NOT lead to dysfunction across a wide range of tasks, as the “single account” models would predict.
- Named after Marcel Mesulam, who argued that this was the case
What are the 8 main reasons why it is unlikely that there is a single unitary frontal lobe “executive system” (Burgess & Robertson, 2002)?
- Correlations between different executive tasks are typically low (e.g. Burgess and Shallice, 1994; Robbins, 1998; Miyake et al, 2000).
- Factor analysis of the various behavioural symptoms following frontal lobe damage show that they do not seem to load on one factor (Burgess et al, 1998).
- Different behavioural symptoms are associated with performance decrements on different clinical executive tasks (Burgess et al, 1998).
- Symptoms such as confabulation or multitasking deficits may be seen independently of virtually any other signs (e.g. Shallice and Burgess, 1991; Burgess and McNeil, 1998; Burgess et al, 2000).
- Deficits such as response suppression and initiation problems can doubly dissociate on executive tests (e.g. Burgess and Shallice, 1996).
- Frontal lobe patients can show a range of different forms of error on the same executive test (e.g. Burgess and Shallice, 1996).
- Brain lesions in different parts of the frontal lobes can be associated with decrements on different executive tasks, and with different types of failure (e.g. Stuss and colleagues, 1994, 1999; Stuss and Alexander, 2000.
- Functional imaging and electrophysiological studies of the frontal lobes suggest potential fractionation of the executive system
What did Shallice and Burgess do in 1991?
- Multiple errands task
- Participants asked to:
- Buy items, e.g. bicycle bell.
- Find out information (e.g. coldest place in Britain yesterday).
- Meet E at a certain time
- Follow rules e.g. “Don’t go into a shop unless you are going to buy something”, “Spend as little money as possible”, “Don’t rush excessively”
- People with rostral PFC damage sucked at this
Which number corresponds with the location of the rostral prefrontal cortex?
What is the brixton anticipation test?
- Looked at in Burgess & Shallice, 1996, 1997
- Dots light up following a pattern, participants are asked which ones they think will light up next
- Bad at predicting when the pattern changes, and make random predictions based on whims
What is the Hayling Sentence Completion Test?
- Looked at in Burgess & Shallice, 1996
- Section 1: Straightforward Completion e.g. The old house will be torn……….. “down”
- Section 2: Anomalous Completion e.g. The whole town came to hear the mayor…… “speak”
- People with imlairments to the Hayling area suck at the latter, suggests they lack inhibition control, and that part of the PFC controls that practice
Why do we think the PFC is associated with humour?
- Damage to right FL disrupts ability to appreciate humour.
- Most people with this damage react to humour less and have diminished physical and emotional responses.
- Verbal humour is related to ability to hold info in WM and non-verbal is assoc. w/ ability to pay attention to detail.
- Concluded that right FL integrates cognitive and affecrive info required to understand jokes and find them amusing.
Why do we think the PFC is associated with social desirability?
- Early PFC lesions have more profound consequences. Lesions before 16m showed severely impaired social behviour, despite normal cognitive function otherwise.
- Early PFC lesions had similar or even more profound consequences (though did show insensitivity to future consequences)
- Unlike adult-onset PFC patients, young ones had defective social/moral reasoning, suggesting acquisition of complex social conventions and moral rules is impaired.
- So early-onset PFC damage can cause psychopathy like symptoms.
How is the PFC related to gratification?
- PPs imagine spending certain amounts of money (£35 in 180 days at the pub), or just estimated what the money could buy in the scenario.
- When imagining spending money, they more often chose delayed option (which had better reward) and thus accumulated more money across task.
- fMRI implicated medial rostral PFC in this effect; greater activity in response to delayed gratification/future-oriented responses. This kind of behaviour is impaired in PFC lesion pts.
- Damage to ventromedial PFC results in poor decision making, despite normal intellectual function.
- E.g. patient EVR: always made poor decisions, never learnt from mistakes. But had no major intellect impairment (normal STM, good at Wisconsin Card Sorting Task).
- Task designed where he had to choose cards from advantageous decks (low reward, low punishment) and disadvantageous decks (high reward, high punishment). Healthy controls learned fast the former was the better option, but EVR chose latter. PFC pts = sensitive to +ve/-ve future consequences. They CAN see the logic, but can't act on it.
Is prospective memory controlled by one neural system?
- Probably not
- Prospective memory: remembering to carry out intention after delay.
- Study had PPs perform a simple action, with a rule to perform a different action on the condition of the outcome of the first.
- Sometimes this happened every time, sometimes the action you had to do after changed etc.
- Bilateral activation of FL was observed, but many other brain regions were active specifically and only during one of the variants of the simple condition. THUS researchers said different brain regions maintain intentions and realise intentions.