Lecture 4 Introduction to human neuropsychology, what does the prefrontal cortex do? Flashcards
What is the frontal cortex made up of?
Prefrontal cortex + motor cortex
What is the prefrontal cortex made up of ?
Lateral PFC and Medial PFC
Grey matter in humans PFC compared to chimpanzees and macaques
.2x greater than in chimpanzees and 1.9x greater than macaques
White matter tracts in humans compared to chimpanzees
1.7x denser subcortical connection in humans compared to chimpanzees
Size of prefrontal cortex in human brain
Volume = 512 cm3
21% of brain
9x larger than visual areas
12x larger than motor areas
Size of prefrontal cortex in the brains of chimpanzees
Volume = 134 cm3
17% of brain
3x larger than visual areas
3x larger than motor areas
Size of prefrontal cortex in macaque monkeys
Volume = 34.3 cm3
13% of brain
The same size as visual and motor areas
Synaptogenesis:
forming new synaptic connections
Dendritic arborization
More tree-like structure in dendrites
Pros of using single case studies:
Proof of principle
Ethical
Cons of using single case studies
Causality
Non-focal
Non-human models commonly used in brain research
- Drosophila (fruit fly) models. 9 Nobel Prizes
- Rodent models
- Non-Human primate models
Pros of using non-human models to study the brain
Full experimental control
Directness
Cons of using non-human models to study the brain
Non-human
Ethics
Pros of asking patients who suffering brain difficulties to report their experiences:
View from the inside
Practicality
Cons of asking patients who suffering brain difficulties to report their experiences:
Lack of control
Subjectivity
Key info on how the Tower of London task works
Participants need to re-arrange the bottom display (from A) to look like the top display (to get to B)
Move discs varying in size from small to large across 3 pegs to build a designated tower in the fewest number of tries as possible
Independent variable: Tower of London task
Number of moves
Patient group
Dependent variable: Tower of London task
Accuracy or reaction time
Owen et al (1990) Tower of London study
Found frontal lobe patients showed impaired planning - requiring significantly more moves to solve the problem compared to controls
Evidence for frontal lobe involvement in planning
nitschke et al (2017, HBM) studies in tower of london task
Did a review of 6 studies on frontal lobe patients and planning
Found majority of studies show impaired accuracy compared to controls
No evidence that left hemisphere lesions were more disruptive than right hemisphere lesions
Pros of patient/control studies
Multiple patients
Practicality
Cons of patient/control studies
Classification issues
Lack of control
Owen et al (1995b) study Tower of London
examined planning performance in patients with lesions to the temporal cortex/medial temporal lobe
Owen et al (1995b) study findings
Patients with lesions to the temporal lobe or amygdala/hippocampus were not significantly impaired on this task (TOL)
What FMRI scans can tell us about damage to prefrontal cortex:
Lesions to the frontal cortex not only damage this region but also damage white matter connections
Van horn et al (2012)
Estimates Gage lost 10% of white connections
Why MRI scans can be useful
Help understand what the frontal lobes are doing during planning
How FMRI shows brain in action
- Brain needs oxygen
- Increase in blood flow so more oxygenated blood changing the ratio of oxygenated and deoxygenated blood
Increased “Magnetic Signal” after neural activity
What are block designs?
- We examine whether there are changes in BOLD signal when people are performing tasks in the scanner
- Have two tasks: the main task A and Task B the control
Blood oxygenation-level dependent (BOLD) signal meaning
Changes in the ratio of oxygenated and deoxygenated haemoglobin
What makes a good control task?
- Same perceptual experience
- Same motor demands
- Same emotional state
Cognitive subtraction meaning
Subtracting the two images from the FMRI scan will reveal which parts of the brain have higher activity/blood flow in task A compared to task B
FMRIS studies of the Tower of London (Fallon et al, 2013)
The dorsolateral prefrontal cortex is recruited during planning, as well as other brain areas
The scan image will show all the brian parts that increased BOLD signal compared to control, mainly lateral prefrontal cortex
Deactivation: “Default mode”
a set of brain regions that decrease their activity in task performance
When the brain is consumed by processing it’s own world - subjective
Need for balance in brain regions
Between ‘executive’ dorsolateral prefrontal cortex and “subjective” medial prefrontal cortex
Spreng and Schacter (2012) Tower of London task study
Used fMRI
Older adults showed impaired accuracy
Older adults don’t show expected decreases in medial prefrontal cortex during planning
Key takehomes from fMRI results
The occipital lobe and the parietal lobe also show increases BOLD signal in planning
Decreases in medial prefrontal cortex
Prefrontal involvement in planning seems to involve both increases and decreases
Pros of using fMRI studies
- Reveals brain networks
- precision
Cons of using fMRI studies
Practicality
Causality
Non-invasive brain stimulation: How necessary is the frontal cortex for planning performance?
- Lesion evidence implies that prefrontal cortex is necessary for normal planning performance
- Neuroimaging suggests both frontal and non-frontal regions involved in planning
- Also increases and decreases in activity in frontal lobs
Non-invasive brain stimulation: Transcranial magnetic stimulation (TMS)
Can isolate the effects after stimulation
Can be excitatory or inhibitory depending on stimulation parameters
Van de Heuvel et al (2013) TMS study
used inhibitory TMS on the left dorsolateral prefrontal cortex prior to planning:
Van de Heuvel et al (2013) TMS study, results
- Inhibition of left dorsolateral prefrontal cortex impairs planning performance
- After TMS inhibition, decreased BOLD signal was found in left premotor cortex, left anterior prefrontal cortex and praecuneus
Pros of Transcranial magnetic stimulation (TMS)
Causality
Focal
