Organisation of the Cerebral Cortex

Question 1

What are the 2 structural units that make up the cerebral cortex?

Answer 1

• white matter (fibres)

- grey matter

Question 2

What are the three types of white matter tracts? What are their functions?

Answer 2

• 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.

Question 3

How many cortical layers are there in humans?

Answer 3

6

Question 4

What are the 6 cortical layers?

Answer 4

• 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.

Question 5

What is the arrangement of grey matter?

Answer 5

• 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

Question 6

What are the functions of the occipital lobe?

Answer 6

• 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

Question 7

What are the functions of the parietal lobe?

Answer 7

• 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

Question 8

What are the functions of the temporal lobes?

Answer 8

• language, object recognition, memory, emotion

- injury leads to agnosia, receptive aphasia

Question 9

What are the functions of the frontal lobe?

Answer 9

• judgement, foresight, personality, appreciation of self in relation to world
• injury leads to deficits in planning and inappropriate behaviour

Question 10

What are the main differences between primary and association cortices?

Answer 10

Primary:

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

Association:

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

Question 11

Prefrontal association area

Answer 11

personality changes, affects behavior

Question 12

Premotor area and SMA

Answer 12

movement planning

Question 13

What do vision association ares do?

Answer 13

pick up things like movement, face recognition etc.

Question 14

What can be used to test the functions of cortical areas?

Answer 14

• fMRI
• SPECT
• PET
• lesions
• etc.

Question 15

What does the visual association cortex do?

Answer 15

• ventral stream: visual identification (what?)
• dorsal stream: localisation in space (where?)

Image attributes are processed separately
What (colour, form); Where (spatial relationships)

Question 16

Prosopagnosia

Answer 16

= face blindness

• Lesions of the visual posterior association area (fusiform gyrus) can result in the inability to recognize familiar faces or learn new faces

Question 17

Lesions in the frontal lobe?

Answer 17

• 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)

Question 18

What do lesions in the parietal lobes cause?

Answer 18

• 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)

Question 19

What do temporal lobe lesions cause?

Answer 19

• Language, object recognition, memory, emotion. Injury leads to agnosia, receptive aphasia
• e.g. anteretrograde amnesia - not being able to form new memories

Question 20

Hemispheric lateralisation

Answer 20

• 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.

Question 21

What happens when you show a split brain patient a word on their right/left field of view and ask them to repeat it?

Answer 21

• 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.

Question 22

Diffusion tensor imaging

Answer 22

• 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.

Question 23

TMS

Answer 23

• 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)

Question 24

TDCS

Answer 24

• 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

Question 25

MEG

Answer 25

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.

Question 26

EEG

Answer 26

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

Question 27

Measuring using MEG and EEG

Answer 27

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

Question 28

fMRI

Answer 28

• 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.