Organisation of the Cerebral Cortex

Question 1

What are the 3 types of fibre that make up white matter?

Answer 1

Association Fibres: connect areas in the same hemisphere
Commissural Fibres: connect the 2 hemispheres
Projection Fibres: connect cortex with lower brain structures (e.g. thalamus)

Question 2

How many layers of grey matter are there?

Answer 2

3-6 (numbered by roman numerals)

Question 3

What is the neocortex?

Answer 3

Part of the cerebral cortex concerned with sight + hearing in mammals, regarded as the most recently evolved part of the cortex

Question 4

Describe the different connections of the 6 layers of grey matter.

Answer 4

Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem + spinal cord

Question 5

What does layer 1 mainly consist of?

Answer 5

Neutropil: an area composed mostly of unmyelinated axons, dendrites + glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies

Question 6

What type of neurone is found in layer 4?

Answer 6

Stellate neurones

Question 7

What type of neurone is found in layer 5?

Answer 7

Pyramidal neurones (Betz cells)

Question 8

What are the 2 parts of the visual association cortex and what are they responsible for?

Answer 8

Dorsal Pathway: responsible for interpretation of spatial relationships + movements (Where)
Ventral Pathway: responsible for form + colour (What)

Question 9

What is the role of the posterior parietal association cortex?

Answer 9

Creates a SPATIAL MAP of the body in its surroundings from multi-modality information

Question 10

What could injury to the posterior parietal association cortex lead to?

Answer 10

Disorientation
Inability to read a map or understand spatial relationships
Apraxia
Hemispatial Neglect

Question 11

Define apraxia.

Answer 11

Inability to make skilled movements with accuracy

Question 12

What is the temporal association cortex responsible for?

Answer 12

Language
Object Recognition
Memory
Emotions

Question 13

What are the 2 main consequences of injury to the temporal lobe?

Answer 13

AGNOSIA: inability to interpret sensory info. although the nerves carrying sensory info. to the brain are fine
E.g. visual agnosia: patients can see perfectly fine but they can’t interpret symbols e.g. letters
RECEPTIVE APHASIA: unable to understand language in spoken or written forms

Question 14

What are the consequences of lesions of the visual posterior association area (fusiform gyrus)?

Answer 14

Prosopagnosia: inability to recognise faces

Question 15

What is the role of the frontal lobe?

Answer 15

Executive functions e.g. judgement, foresight, personality, appreciation of self in relation to world

Question 16

What are 4 consequences of a prefrontal lobotomy? Where may this be seen clinically?

Answer 16

Change in personality
Inappropriate behaviour
Lack of ability to remember + relate things over time
Attention span + ability to concentrate are diminished
Seen in frontotemporal dementia

Question 17

What 2 areas does the prefrontal cortex receive massive inputs from?

Answer 17

Sensory association cortex (somatosensory, visual + auditory)
Dorsomedial Nucleus of the thalamus
(lesion of the dorsomedial nucleus has similar consequences to prefrontal lobotomy)

Question 18

If you give someone with a unilateral parietal lobe lesion something to draw, what will you expect him or her to do?

Answer 18

Hemispatial neglect: they will only draw half of it

Question 19

What effect do temporal cortex lesions have on memory?

Answer 19

Impaired short-term memory

Effectively trapped in a 30s window of memory

Question 20

Describe hemispheric specialisation.

Answer 20

Right hemisphere = creative + artistic

Left hemisphere = logical + scientific

Question 21

What is a callosotomy?

Answer 21

A palliative procedure used for the treatment of seizures- cuts through corpus callosum
Thus prevents interhemispheric spread of epileptic activity

Question 22

State a type of imaging that uses the movement of water molecules in the brain to infer the underlying structure of white matter.

Answer 22

Diffusion Tensor Imaging (Tractography)

Question 23

State 2 types of brain stimulation testing and what it can be used for.

Answer 23

Transcranial Magnetic Stimulation (TMS)
Magnetic field induces a current in the cortex, causing neurones to fire
Used to test whether a specific brain area is responsible for a function
Transcranial Direct Current Stimulation (TDCS)
Changes the local excitability of neurones, increasing/ decreasing firing rate (does NOT directly induce neuronal firing)
Anode = increases excitability
Cathode = decreases excitability

Question 24

Describe and explain how PET scans work. What can it be used for?

Answer 24

A radioactive tracer is attached to a molecule to locate areas of the brain where that molecule is being absorbed
Tracer emits positrons, which are then detected by receptors
Used in PD to see uptake of dopamine precursors by dopaminergic neurones

Question 25

What is the difference between MEGs and EEGs?

Answer 25

``` MEGs = magnetoencephalography: measures magnetic fields EEGs = electroencephalography: measures electric fields ```

Question 26

What is a major problem with MEGs and EEGs and how is this resolved?

Answer 26

Quite noisy: lots of background activity Resolved by doing a trial of a large number of participants so that an average can be found Once average has been found, it can be deducted from the captured signal to see the underlying activity

Question 27

What is fMRI? What does it detect? How?

Answer 27

Functional MRI Detects changes in blood flow in the brain Relies on the fact that blood flow in the brain + neuronal activity are coupled– more active parts of brain require increased blood flow

Question 28

Which 2 areas of the brain become more active when participants imagine positive events?

Answer 28

Amygdala | Rostral anterior cingulate cortex

Question 29

Describe the columnar arrangement of cortical layers

Answer 29

Neocortex is arranged in layers + columns | Neurones with similar properties are connected in the same column

Question 30

What characterises primary cortices? (Function, organisation)

Answer 30

Function predictable Organised topographically Left-right symmetry

Question 31

What characterises association cortices? (function, organisation)

Answer 31

Function less predictable Not organised topographically Left-right symmetry weak or absent

Question 32

A patient with a callosotomy is shown a word on RHS of view. On being asked what he saw, what would be say?

Answer 32

He saw the word He tells you he saw the word as the left hemisphere is dominant for verbal processing + his right visual field feeds back to the left hemisphere

Question 33

A patient with a callosotomy is shown a word on LHS of view. On being asked what he saw, what would be say?

Answer 33

He would not say anything. | Right hemisphere can't share info. with left, so is unable to say what he saw but can draw what he saw.

Question 34

What could TDCS potentially be used for?

Answer 34

To reduce motion sickness by suppressing the area of the cortex associated with perceiving vestibular information