15. Cerebral cortex

Question 1

What is grey matter?

Answer 1

• Component of the CNS, consisting of neuronal cell bodies and glial cells
• On the surface of the brain

Question 2

What is white matter?

Answer 2

• Areas of the CNS made up of myelinated axons (tracts)

* Relay and coordinating communication between different areas of the brain

Question 3

What are the 3 types of fibres in the cerebral white matter and their functions?

Answer 3

• Association fibres - connect areas within the same hemisphere (local circuitry)
• Commissural fibres - connect left and right hemispheres
• Projection fibres - connect cortex with lower brain structures e.g. thalamus, brain stem, spinal cord

Question 4

Where is the archicortex located and how many layers does it have?

Answer 4

• Most prevalent in the olfactory cortex and the hippocampus (smell and memory)
• 3 cortical layers

Question 5

What does each layer of the neocortex contain?

Answer 5

1) Mainly neuropil (fibres)
2 +3) Smaller pyramidal neurones, primary corticocortical connections (interconnectivity)
4) Rich in stellate neurones with locally ramifying axons - receive input from the thalamus
5 +6) Pyramidal neurones whose axons typically leave the cortex (output) - (6) to a lesser degree

Question 6

How is the cortex arranged?

Answer 6

• Layers - laminar organisation
• Cortical columns - more dense vertical connections, basis for topographical organisation
• Neurones with similar properties are connected in the same column

Question 7

Which lobes form the neocortex?

Answer 7

Frontal, parietal, occipital, temporal

Question 8

What is the difference between the function, topography and symmetry of the primary and association cortices?

Answer 8

Primary
• predictable function
• organised topographically
• left-right symmetry

Association
• less predictable function
• not organised topographically
• left-right symmetry absent

Question 9

What is analysed in the visual association cortex, ventral pathway and dorsal pathway?

Answer 9

• VAC - different attributes of visual images in different places
• Ventral pathway - form and colour
• Dorsal pathway - spatial relationships and movement

Question 10

What is the function of the posterior parietal association cortex and what can damage lead to?

Answer 10

• Somatosensory
• Creates a spatial map of the body in the surroundings, from multi-modality information
• Injury may cause disorientation, inability to read maps or understand spatial relationships, apraxia, hemispatial neglect - patient will only draw half a clock

Question 11

What does the temporal lobe deal with and what can damage lead to?

Answer 11

• Language, object recognition, memory, emotion
• Injury leads to agnosia (inability to process sensory information), receptive aphasia (difficulty understanding language)
• Treated by removal of damaged portion

Question 12

Where is Broca’s and Wernicke’s area located?

Answer 12

• Broca’s - inferior frontal lobe
• Wernicke’s - junction between parietal + temporal
• Lateralised to the left hemisphere

Question 13

What’s located anterior to the primary motor cortex?

Answer 13

Pre-motor cortex

Question 14

What can lesions of the visual posterior association area (fusiform gyrus) lead to?

Answer 14

Inability to recognise familiar faces or learn new faces (prosopagnosia)

Question 15

What is the entorhinal cortex?

Answer 15

• Lateral part of the temporal cortex
• Receives information from all other parts of the cortex and integrates them
• Hub in a widespread network for memory, navigation and the perception of time
• Important in decision making

Question 16

What is a callosotomy?

Answer 16

• Surgical treatment - severe epilepsy
• Commissural pathway is cut
• Stops global seizure that initiates in one hemisphere

Question 17

How will someone born without a corpus callosum be affected?

Answer 17

• They will have automatic compensatory mechanisms

* Still have subtle psychological deficits (this is more obvious in patients who have had surgery)

Question 18

Which half of the brain is dominant for the following:
• writing
• both ears
• drawing
• calculation
• music
• spatial perception

Answer 18

• writing - left
• both ears - left
• drawing - right
• calculation - left
• music - right
• spatial perception - right

Question 19

A patient who’s had callosotomy is shown the word “face” which flashes in their right, then left field of view. How will they interpret the image each time?

Answer 19

• Right field - left hemisphere is dominant for verbal processing, patient can give an answer matching the word
• Left field - patient doesn’t see anything, but they will be able to draw a face

Question 20

What is diffusion tensor imaging (DTI)?

Answer 20

• aka tractography
• Similar to MRI
• Measures alignment of water molecules
• Can build a fibre network of the brain
• Used in brain tumour patients to show break down of connections

Question 21

What is transcranial magnetic stimulation used for?

Answer 21

• Magnetic field induces an electric current in the cortex, causing the neurones to fire
• Used to test whether a specific brain area is responsible for a function

Question 22

What is transcranial direct current stimulation used for (TDCS)?

Answer 22

• Changes the local excitability of the neurones
• Does not directly induce neuronal firing
• Changes the threshold for increasing or decreasing the firing rate
• Research suggest this could be used to reduce motion sickness or vertigo - suppresses area of cortex associated with processing vestibular information

Question 23

What can PET imaging be used for in the brain?

Answer 23

• Research tool (due to expense and method)
• Look at the potential used of psychedelic drugs in therapy
• e.g. radioactively labelled DOPA will show a deficit in the dopaminergic nuclei of a Parkinson’s patient

Question 24

What can magnetoencephalography (MEG) and electroencephalography (EEG) be used for?

Answer 24

• MEG - measures magnetic fields - involves a big machine
• EEG - measures electric fields - involves lots of electrodes
• Used to map and record activity of the brain
• Multiple repeat measurements needed due to noisy signals, so have to find patterns

Question 25

What can fMRIs be used for?

Answer 25

• Information in vivo about connectivity
• Usually about monitoring blood flow and glucose metabolism
- when there is more flow, there is probably higher activity

Question 26

How can we measure optimism?

Answer 26

• Measure the brains response to imagining positive and negative events in the future or the past
• When participants imagine positive events, the amygdala and Rostral anterior cingulate cortex were more active than when they imagined negative events