the frontal lobes Flashcards
how much of the brain does the frontal lobe make up?
1/3 of the brain
Laterally, what is the major subdivision of the frontal lobe?
central sulcus
Medially, what is the major subdivision of the frontal lobe?
cingulate sulcus
what are the 3 main subdivisions of the frontal lobe?
1/ primary motor cortex
2/ premotor cortex
3/ prefrontal cortex
describe the cellular structure of the primary motor cortex
- has giant Betz cells in layer V (5)
describe the cellular structure of the premotor cortex
- has no granular cells in layer IV (4)
describe the cellular structure of the prefrontal cortex
- has granular cells in layer IV (4)
where is the primary motor cortex on Brodmann’s map?
Brodmann area 4 (BA 4)
where is the premotor cortex on Brodmann’s map?
Brodmann area 6 (BA 6)
where is the prefrontal cortex on Brodmann’s map?
Brodmann area (BA…)
8,
9,
10,
11,
45,
46,
47
outline the functions of the motor cortex
- control skeletal muscles together with other structures
- does all the controlling
other structures:
- basal ganglia (responsible for primary motor control)
- thalamus (relay station for information)
- cerebellum (modulates commands to motor neurones, balance, equilibrium)
outline the functions of premotor cortex
- does more higher order motor control
- movement planning
- movement selection
- inhibitory control of motor cortex (permits an individual to inhibit their impulse and select more appropriate behaviour)
what is the traditional approach to studying the neuropsychology of the prefrontal cortex?
- studying patients with frontal lobe lesion deficits
outline the verbal fluency task (Milner, 1964)
- had ppts write down as many words beginning with a particular letter for a minute, then changed the letter
- used to provide insight to language production ability
- provide insight into cognitive impairments
outline the Wisconsin Card Sorting Test (Milner, 1964)
- designed to measure persons ability to shift cognitive strategies and adapt to changing circumstances
- involves 128 cards
- each card marked with 4 possible stimuli
- ppt instructed to sort cards into one of 4 piles, each representing the 4 stimuli
- ppts is not told the sorting rule, this is deduced based on feedback from examiner
- sorting rule is changed multiple times throughout experiment without warning
- requiring ppt to shift their cognitive strategy
- ppts performance measured by number of errors
- test is used to asses executive function and cognitive flexibility
outline the Stroop Task (Perret, 1974)
- measures ability to inhibit cognitive interference and selectively attend to specific information
- The task involves presenting the participant with a series of colour names printed in different coloured inks
- ppt instructed to name the colour of the ink as quickly and accurately as possible, while ignoring the written word
outline the Tower of London task (Shallice, 1982)
- task measures planning, problem-solving and executive function
- ppt presented with a board that has 3 pegs of different heights and set of coloured balls arranged in specific pattern
- ppt instructed to move the balls from starting position to a target configuration
- only one ball moved at a time, balls cannot be placed on larger balls, must be completed in certain time limit
- ppt performance measured based on number of moves taken and time taken to complete task
- task shown to be sensitive to cognitive impairment
identify some issues with traditional approach to studying the neuropsychology of the prefrontal cortex
- traditional approach = issues with sensitivity (ability to identify those with the prefrontal cortex lesions)
- issues with specificity (ability of traditional tests to not identify those impaired by lesions in other areas)
- not all patients with frontal lesions have difficulties
- some patients with non-lesions have difficulties
outline Stuss’s Basic Approach
- devised simple tests that test a single process within the frontal lobe
- difficulty and context of test becomes manipulated to start testing more complex processes
what is lesion-symptom mapping?
- you have a lesion
- you have a symptom caused by lesion
- only test that symptom
- narrow down
what were Stuss et al.’s conclusions on what the areas in the prefrontal cortex are doing?
- in the lateral PFC, you have executive function
- left side = task setting (when given instructions for task, you prepare yourself with the instructions and the task)
- right side = monitoring (right/wrong behaviour based on instructions given)
- dorsomedial PFC: energisation (process of initiating and sustaining a response)
- orbital PFC: toward eye-socket, behavioural and self-regulation
- polar PFC: used for metacognition (thinking about thinking)
evaluate Struss et al. approach to studying the prefrontal cortex
exact processes still unclear
- unsure if tasks are really process-pure
general problems with patient studies
- small sample sizes
- lesions
what is the overarching theory of lateral prefrontal cortex function?
- LPFC has important role in executive function, cognitive control, top-down control, goal-directed behaviour
is the LPFC a functional unit?
- no
- some LPFC areas not typically part of top-down control
what is Duncan’s main idea over the function of the LPFC?
- LPFC adapts to tasks
- believes that LPFC is part of a multi-demand (MD) network
what are areas of multi-demand network activated by? (Duncan, 2013)
diverse cognitive demands
what does it mean that the LPFC has no distinct function?
- no distinct function
- so lateral prefrontal cortex function is to do what it is supposed to do
- supposed to adapt to task demands
outline Freedman et al. (2001) study into the idea the LPFC has no distinct function
- studied rheus monkeys
- study aimed to examine role of PFC
- monkeys trained to perform delayed match-to-sample task
- neural activity recorded
- monkeys shown visual stimulus then had to hold image in working memory during delay period
- then shown a second image
- monkey had to indicate whether the second image matched the sample (choice between dog and cat)
FINDINGS
- PFC neurones were selectively active during delay period of working memory task
- monkey could also distinguish between classes (between dog and cat)
- found that PFC could meet the demand of task changing
what was Koechlin / Badre / Nee’s main idea of what the LPFC function was?
- LPFC doesn’t adapt
- LPFC = hierarchically organised/differentiated
- exact functional descriptions differ
- anterior LPFC = deals with abstract information
- posterior LPFC = deals with concrete information
Outline Badre (2008) study
- had ppts partake in series of tasks
task 1: sensory judgement
- colour of stimuli presented
- told to press something when you see this colour
task 2: feature judgements
- texture + colour
- looking at texture of stimuli that is now paired with colour
- more abstract
task 3: dimension and context judgements
- have two objects
- told to press either match or non-match
- only match if there are two objects of the same type plus a colour
- if colour changes but objects don’t, still a non-match
- the idea that PFC functioning is hierarchically organised
- hierarchy is in order of tasks
what conclusions can be drawn about the function of the prefrontal cortex?
PFC = adaptive (Duncan)
- good idea
- but quite restrictive
PFC = hierarchically organised
- plausible
- exact process associated with different areas = still unclear
what is needed to figure out what the PFC function is?
- computational models combined with experimental evidence
what is meant by no lobe is an island?
- PFC does nothing on its own
- it is necessary for cognitive control but is not sufficient on its own
- PFC = part of neural network, tightly connected with most other cortical and subcortical areas
