Organisation of the Cerebral Cortex Flashcards
What are the 2 structural units that make up the cerebral cortex?
- white matter (fibres)
- grey matter
What are the three types of white matter tracts? What are their functions?
- Association fibers: connect regions of the cortex within the same hemisphere
- commissural fibers: connect the cerebral hemispheres (corpus callossum and anterior+posterior commissure)[
- projection fibers: connect the cortex with lower parts of the brain and the spinal cord. Can be afferent or efferent.
How many cortical layers are there in humans?
6
What are the 6 cortical layers?
- Layer 1 = dorsal = outside (acellular region, there are basically no neurones but there may be glial cells)
- Layers 2+3 (largely association fibers, layers 1-3 are mainly used for corticosteroids-cortical connections).
- Layer 4 (received input from the thalamus, input layer)
- Layer 5+6 (output layer, Betz neurones, connections with subcortical, brainstem and spinal cord.
- Each of the cortical laminae in the neocortex has characteristic anatomical and functional features.
What is the arrangement of grey matter?
- Neocortex is arranged in layers (lamina structure) and columns
- More dense vertical connections – basis for topographical organization
- Neurons with similar properties are connected in the same column
What are the functions of the occipital lobe?
- visual association cortex analyses different attributes of visual image in different places
- form & colour analyzed along ventral pathway
- spatial relationships & 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 multi-modality information
injury may cause disorientation, inability to read map or understand spatial relationships, apraxia, hemispatial neglect
What are the functions of the temporal lobes?
- language, object recognition, memory, emotion
- injury leads to agnosia, receptive aphasia
What are the functions of the frontal lobe?
- judgement, foresight, personality, appreciation of self in relation to world
- injury leads to deficits in planning and inappropriate behaviour
What are the main differences between primary and association cortices?
Primary:
- function is predictable
- organised topographically
- left-right symmetry
Association:
- function less predictable
- not organised topographically
- left-right symmetry weak or absent
Prefrontal association area
personality changes, affects behavior
Premotor area and SMA
movement planning
What do vision association ares do?
pick up things like movement, face recognition etc.
What can be used to test the functions of cortical areas?
- fMRI
- SPECT
- PET
- lesions
- etc.
What does the visual association cortex do?
- ventral stream: visual identification (what?)
- dorsal stream: localisation in space (where?)
Image attributes are processed separately
What (colour, form); Where (spatial relationships)
Prosopagnosia
= face blindness
- Lesions of the visual posterior association area (fusiform gyrus) can result in the inability to recognize familiar faces or learn new faces
Lesions in the frontal lobe?
- Characterised by a lack of planning, behaviour becomes disorganised, attention span and concentration diminish, self-control is hugely impaired
- cause behavioural change (e.g. DISINHIBITION, aggression, sexually inappropriate behaviour)
What do lesions in the parietal lobes cause?
- posterior parietal association cortex creates a spatial map of the body in surroundings, from multi-modality information
- injury may cause disorientation, inability to read maps or understand spatial relationships, apraxia, hemispatial neglect (if you asked someone to draw e.g. a house they would only draw a half)
What do temporal lobe lesions cause?
- Language, object recognition, memory, emotion. Injury leads to agnosia, receptive aphasia
- e.g. anteretrograde amnesia - not being able to form new memories
Hemispheric lateralisation
- the right and left lobe have different functions
- e.g. R: drawing, music, spatial perception
- e.g. L: writing, both ears, calculation
- patients post callosotomy (split brain patients) have lateralised deficits in function.
What happens when you show a split brain patient a word on their right/left field of view and ask them to repeat it?
- Right field of view: goes to left side of brain -> they are able to repeat the word
- Left fiel of view: goes to the right side of the brain -> they cannot repeat it but they can draw it.
Diffusion tensor imaging
- DTI
- 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 be used to estimate the location and
Connections between different white matter pathways. - For patients with traumatic brain injury or concussion injuries in sports such as boxing, it is thought that white matter connections become disrupted.
TMS
- transcranial magnetic stimulation
- 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
-> used for research but could also potentially be used for treatment, e.g. rehabilitation of spinal cord lesion patients (use it to stimulate damaged pathways)
TDCS
- transcranail direct current stimulation
- Changes the local excitability of neurons, increasing or decreasing the firing rate
(NB, does not directly induce neuronal firing) - you don’t evoke activity here but you change the sensitivity of the neurones
MEG
Magnetoencephalography
-> functional neuroimaging technique used to map brain activity by recording magnetic fields produced by electrical currents occurrrng naturally in the brain using very sensitive magnetometers.
EEG
Electroencephalography
-> electrophysiological monitoring method to record electrical activity of the brain. It is typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used in specific applications (intracortical EEG, for example to localise function during neurosurgery). EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain
Measuring using MEG and EEG
Magnetoencephalography (MEG) and Electroencephalography (EEG)
Event-related potential / evoked-potentials
EEG and MEG are noisy signals.
Participants perform large numbers of trials so that an average can be used
->By averaging a large number of trials, the effect of random noise can be eliminated to reveal the underlying wavefunction – which represents the brain activity associated with a particular stimulus.
MEG/ EEG measures the surface activity of the brain, but cannot directly measure the activity of interior structures.
=> check ppt
fMRI
- measures brain activity by detecting changes associated with blood flow.
- This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases
- The ‘blobs’ on fMRI results are areas which are slightly more active than the surrounding brain regions (e.g. 1-2%). The rest of the brain is still active, but in the same way
- As an EEG/MEG average, for a particular task these regions show slightly different activity.
