15. Cerebral cortex Flashcards
What is grey matter?
- Component of the CNS, consisting of neuronal cell bodies and glial cells
- On the surface of the brain
What is white matter?
- Areas of the CNS made up of myelinated axons (tracts)
* Relay and coordinating communication between different areas of the brain
What are the 3 types of fibres in the cerebral white matter and their functions?
- 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
Where is the archicortex located and how many layers does it have?
- Most prevalent in the olfactory cortex and the hippocampus (smell and memory)
- 3 cortical layers
What does each layer of the neocortex contain?
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
How is the cortex arranged?
- Layers - laminar organisation
- Cortical columns - more dense vertical connections, basis for topographical organisation
- Neurones with similar properties are connected in the same column
Which lobes form the neocortex?
Frontal, parietal, occipital, temporal
What is the difference between the function, topography and symmetry of the primary and association cortices?
Primary
• predictable function
• organised topographically
• left-right symmetry
Association
• less predictable function
• not organised topographically
• left-right symmetry absent
What is analysed in the visual association cortex, ventral pathway and dorsal pathway?
- VAC - different attributes of visual images in different places
- Ventral pathway - form and colour
- Dorsal pathway - spatial relationships and movement
What is the function of the posterior parietal association cortex and what can damage lead to?
- 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
What does the temporal lobe deal with and what can damage lead to?
- 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
Where is Broca’s and Wernicke’s area located?
- Broca’s - inferior frontal lobe
- Wernicke’s - junction between parietal + temporal
- Lateralised to the left hemisphere
What’s located anterior to the primary motor cortex?
Pre-motor cortex
What can lesions of the visual posterior association area (fusiform gyrus) lead to?
Inability to recognise familiar faces or learn new faces (prosopagnosia)
What is the entorhinal cortex?
- 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
What is a callosotomy?
- Surgical treatment - severe epilepsy
- Commissural pathway is cut
- Stops global seizure that initiates in one hemisphere
How will someone born without a corpus callosum be affected?
- They will have automatic compensatory mechanisms
* Still have subtle psychological deficits (this is more obvious in patients who have had surgery)
Which half of the brain is dominant for the following: • writing • both ears • drawing • calculation • music • spatial perception
- writing - left
- both ears - left
- drawing - right
- calculation - left
- music - right
- spatial perception - right
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?
- 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
What is diffusion tensor imaging (DTI)?
- 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
What is transcranial magnetic stimulation used for?
- 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
What is transcranial direct current stimulation used for (TDCS)?
- 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
What can PET imaging be used for in the brain?
- 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
What can magnetoencephalography (MEG) and electroencephalography (EEG) be used for?
- 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
What can fMRIs be used for?
• Information in vivo about connectivity
• Usually about monitoring blood flow and glucose metabolism
- when there is more flow, there is probably higher activity
How can we measure optimism?
- 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
