Organisation of the Cerebral Cortex Flashcards
What are the three types of fibre that make up white matter?
Association Fibres – connect with areas in the same hemisphere
Commissural Fibres – connect the two hemispheres
Projection Fibres – connect the cortex with lower brain structures (e.g. thalamus)
How many layers of grey matter are there?
3-6 (they are usually numbered by roman numerals)
What is the neocortex?
A part of the cerebral cortex (grey matter) concerned with sight and hearing in mammals, regarded as the most recently evolved part of the cortex
Describe the arrangement of the neocortex.
- Arranges in layers (lamina structure) and columns
- More dense ventral connections - basis for topographical organisation
- Neurons with similar properties are connected in the same column
Describe the different connections of the 6 layers of grey matter.
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem and spinal cord
What does layer 1 mainly consist of?
Neutropil – an area composed mostly of unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies
What type of neurone is found in layer 4?
Stellate neurones
What type of neurone is found in layer 5?
Pyramidal neurones
What are the differnet lobes of the neocortex?
- Frontal
- Parietal
- Occipital
- Temporal
Describe the organisation of the primary cortices.
Primary cortices
- function predictable
- organised topographically
- left-right symmetry
- Taste (gustatory) cortex in the inferior frontal lobe
- Smell (olfactroy) cortex in the medial temporal lobe
Describe the organisation of the association cortices.
Association cortices
- function less predictable
- not organised topographically
- left-right symmetry weak or absent
- Broca’s area in inferior frontal lobe; Wernicke’s at junction between parietal and temporal lobe
- Broca’s and Wernicke’s found on L side thus stroke on left side causes language deficits.
What are the two parts of the visual association cortex and what are they responsible for?
WHAT and WHERE pathways for analysng different attributes of visual image in different places:
Dorsal Pathway – responsible for interpretation of spatial relationships and movements
Ventral Pathway – responsible for form and colour
What is the result of lesions of the visual posterior association area(fusiform gyrus)?
- inability to recognize familiar faces
- inability to learn new faces
=a deficit called prosopagnosia (aka face blindness).
What is the role of the frontal lobe?
Executive functions e.g. planning, judgement, foresight, personality
What two areas does the prefrontal cortex receive massive inputs from?
- Sensory association cortex (somatosensory, visual and auditory)
- Dorsomedial Nucleus of the thalamus
NOTE: lesion of the dorsomedial nucleus will have similar consequences to prefrontal lobotomy
What could injury of the posterior parietal association cortex lead to?
- Disorientation
- Inability to read a map or understand spatial relationships
- Apraxia
- Hemispatial neglect
Describe hemispheric specialisation.
Right hemisphere = spacial perception, drawing, music.
Left hemisphere = language dominant + calculations, writing, both ears.
Describe the effects of a callosotomy.
Input from the left field of vision is processed by the right hemisphere and vice versa.
In split brain patients:
- Word flashed on right side will enter the left hemisphere –> patient will be able to say what they say because it is the verbal processing dominant side.
- If word flashes on the left then the right hemisphere processes it –> unable to share information with the left –> patient is unable to say what he saw but he can draw it (since this is the spacial percpetion side)
State a type of imaging that uses the movement of water molecules in the brain to infer the underlying structure of white matter.
Diffusion Tensor Imaging – Tractography
Describe how PET scanning can be used in Parkinson’s Disease.
- It can be used in Parkinson’s disease to see the uptake of dopamine precursors by dopaminergic terminals in the striatum - 18-fluoro-levodopa given to show degree of presence of terminals.
- Degree of uptake should be homogenous throughout striatum
- BUT in PD there is profound loss in the posterolatral putamein with relative preservation of the caudate.
- If the PD mainly affects the right arm then there will be reduced dopaminergic innervation most on the right posterolateral putamen (as shown below)
What is a major problem with MEGs and EEGs and how is this resolved?
- It is quite noisy – there is a lot of background activity
- This is resolved by doing a trial of a large number of participants so that an average can be found
- Once the average has been found, eliminating effect of random noise can allow you to see underlying activity.
MEG/EEG also only measures surface activity of the brain, but cannot directly measure the activity of interior surfaces.
What is fMRI?
Function MRI
It detects changes in blood flow in the brain
It relies on the fact that blood flow in the brain and neuronal activity are coupled – more active parts of the brain require increased blood flow
“blobs” on fMRI are the areas which are 1-2% more active than surrounding areas.
