Organisation of the cerebral cortex Flashcards
What is grey matter in the brain?
Nerve cell bodies
On the outside (covers white matter)
What is white matter in the brain?
Circuitry/wiring
Underneath grey matter
What are the 3 types of fibres in cerebral white matter?
Association fibres- connect areas within the same hemisphere
Commissural fibres- connect left hemisphere to right hemisphere
Projection fibres- connect cortex with lower brain structure (e.g. thalamus), brainstem and spinal cord
What are the cortical layers of grey matter?
6 layers.
Layers 1-3 mainly cortico-cortical connects.
Layer 4 has input from the thalamus.
Layers 5 and 6 have connections with subcortical, brainstem and spinal cord.
The generally smaller pyramidal neurons in layers II and III (which are not very distinct) have primarily corticocortical connections.
Layer I contains mainly neuropil.
Cortical layer IV is typically rich in stellate neurons with locally ramifying axons.
In the primary sensory cortices, these neurons receive input from the thalamus, the major sensory relay from the periphery.
Layer V, and to a lesser degree layer VI, contain pyramidal neurons whose axons typically leave the cortex.
How is the neocortex arranged?
Lamina structure (in layers) and in columns.
6 layers, multiple columns.
What are the four primary lobes/cortices that comprise the neocortex?
Frontal lobe
Parietal lobes
Occipital lobe
Temporal lobe
How are the primary cortices in the brain organised?
Organised topographically.
Left-right symmetry.
Function predictable.
Label the following diagram:
How are the association cortices organised?
Not topographically.
Left-right symmetry weak or absent.
Function less predictable than primary cortices.
What are the functions of the occipital lobe?
Visual association cortex analyses different attributes of visual image in different places
Form and colour analysed along ventral pathway
Spatial relationships and movement along dorsal pathway
Lesions affect specific aspects of visual perception
What are the functions of the parietal lobe?
Posterior parietal association cortex creates spatial map of body in surroundings, from multimodality information.
What may injury to the parietal lobe result in?
Injury may cause disorientation, inability to read map or understand spatial relationships, apraxia, hemispatial neglect
What are the functions of the temporal lobe?
Language
Object recognition
Memory
Emotion
What may result from injury to the temporal lobe?
Injury leads to agnosia, receptive aphasia.
What are the functions of the frontal lobe?
Judgement
Foresight
Personality
Appreciation of self in relation to world
What is the result of injury to the frontal lobe?
Injury leads to deficits in planning and inappropriate disorganised behaviour, concentration diminishes, self-control is hugely impaired.
What are the two pathways in the visual association cortex?
Where pathway (dorsal stream- spatial relationships)
What pathway (ventral stream- colour, form)
What can result from lesions of the visual posterior association area (fusiform gyrus)?
Inability to recognise familiar faces or learn new faces- a deficit called prosopagnosia, a.k.a. facial blindness.
Describe hemispheric specialisation.
The left hemisphere is language dominant
The right hemisphere is largely spatial processing
Patients who have had a callostomy (split brain) have lateralised deficits in function
What is diffusion tensor imaging (tractography)?
Subset of MRI.
Measures fractional anisotropy (FA).
Structural imaging can be used to measure the effect of lesions in white matter, or how these lesions might disconnect different brain areas and lead to complex symptoms.
The movement of water molecules in the brain can be used to infer the underlying structure of white matter.
This information can be used to estimate the location and connections between different white matter pathways.
What is transcranial magnetic stimulation (TMS)?
The magnetic field induces an electric current in the cortex, causing neurons to fire.
This can be used to test whether a specific brain area is responsible for a function, e.g. speech.
What is transcranial direct current stimulation (TDCS)?
Changes the local excitability of neurons, increasing or decreasing the firing rate- does not directly induce neuronal firing.
Could be used to reduce motion sickness by suppressing the area of the cortex associated with processing vestibular information.
What is positron emission tomography (PET)?
Uses a radioactive tracer attached to a molecule to locate brain areas where that particular molecule, e.g. dopamine, is being absorbed in the brain.
Expensive.
Good spatial resolution and specificity in terms of the underlying biology (only way to identify brain regions absorbing particular substances).
PET scans following administration of 18-fluoro-levodopa to label dopaminergic terminals in the striatum.
What is magnetoencephalography?
Measures magnetic fields.
Functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers.
