Organisation of the cerebral cortex

Question 1

What is grey matter in the brain?

Answer 1

Nerve cell bodies

On the outside (covers white matter)

Question 2

What is white matter in the brain?

Answer 2

Circuitry/wiring

Underneath grey matter

Question 3

What are the 3 types of fibres in cerebral white matter?

Answer 3

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

Question 4

What are the cortical layers of grey matter?

Answer 4

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.

Question 5

How is the neocortex arranged?

Answer 5

Lamina structure (in layers) and in columns.

6 layers, multiple columns.

Question 6

What are the four primary lobes/cortices that comprise the neocortex?

Answer 6

Frontal lobe

Parietal lobes

Occipital lobe

Temporal lobe

Question 7

How are the primary cortices in the brain organised?

Answer 7

Organised topographically.

Left-right symmetry.

Function predictable.

Question 8

Label the following diagram:

Answer 8

Question 9

How are the association cortices organised?

Answer 9

Not topographically.

Left-right symmetry weak or absent.

Function less predictable than primary cortices.

Question 10

What are the functions of the occipital lobe?

Answer 10

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

Question 11

What are the functions of the parietal lobe?

Answer 11

Posterior parietal association cortex creates spatial map of body in surroundings, from multimodality information.

Question 12

What may injury to the parietal lobe result in?

Answer 12

Injury may cause disorientation, inability to read map or understand spatial relationships, apraxia, hemispatial neglect

Question 13

What are the functions of the temporal lobe?

Answer 13

Language

Object recognition

Memory

Emotion

Question 14

What may result from injury to the temporal lobe?

Answer 14

Injury leads to agnosia, receptive aphasia.

Question 15

What are the functions of the frontal lobe?

Answer 15

Judgement

Foresight

Personality

Appreciation of self in relation to world

Question 16

What is the result of injury to the frontal lobe?

Answer 16

Injury leads to deficits in planning and inappropriate disorganised behaviour, concentration diminishes, self-control is hugely impaired.

Question 17

What are the two pathways in the visual association cortex?

Answer 17

Where pathway (dorsal stream- spatial relationships)

What pathway (ventral stream- colour, form)

Question 18

What can result from lesions of the visual posterior association area (fusiform gyrus)?

Answer 18

Inability to recognise familiar faces or learn new faces- a deficit called prosopagnosia, a.k.a. facial blindness.

Question 19

Describe hemispheric specialisation.

Answer 19

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

Question 20

What is diffusion tensor imaging (tractography)?

Answer 20

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.

Question 21

What is transcranial magnetic stimulation (TMS)?

Answer 21

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.

Question 22

What is transcranial direct current stimulation (TDCS)?

Answer 22

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.

Question 23

What is positron emission tomography (PET)?

Answer 23

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.

Question 24

What is magnetoencephalography?

Answer 24

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.

Question 25

What is electroencephalography (EEG)?

Answer 25

Measures electric fields.

Electrophysiological monitoring method to record electrical activity of the brain.

Typically non-invasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used in specific applications (intracortical EEG, e.g. to localise function during neurosurgery).

EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain.

Question 26

What is functional magnetic resonance imaging (fMRI)?

Answer 26

Measures brain activity by detecting changes associated with blood flow.

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.