Organisation of the Cerebral Cortex

Question 1

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

Answer 1

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

Question 2

How many layers of grey matter are there?

Answer 2

3-6 (they are usually numbered by roman numerals)

Question 3

What is the neocortex?

Answer 3

A part of the cerebral cortex concerned with sight and 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 and spinal cord

Question 5

What does layer 1 mainly consist of?

Answer 5

Neutropil – an area composed mostly of unmyelinated axons, dendrites and 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 e.g. upper motor neurones

Question 8

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

Answer 8

Dorsal Pathway – responsible for interpretation of spatial relationships and movements “where is it?”
Ventral Pathway – responsible for form and colour “what is it?”

Question 9

What is the role of the posterior parietal association cortex?

Answer 9

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

Question 10

What could injury of 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 two main consequences of injury to the temporal lobe?

Answer 13

AGNOSIA – inability for the brain to interpret sensory information although the nerves carrying sensory information to the brain are fine
E.g. visual agnosia – patients can see perfectly fine but they can’t interpret sympbols such as letters

RECEPTIVE APHASIA –unable to understand language in the spoken or written forms

Question 14

What are the consequences of visual association cortex lesions?

Answer 14

Prosopagnosia – inability to recognise faces &learn new faces

Question 15

What is the role of the frontal lobe?

Answer 15

Executive functions e.g. planning, judgement, foresight, personality

Question 16

What are the consequences of a prefrontal lobotomy?

Answer 16

Change in personality
Inappropriate behaviour
Lack of ability to remember and relate things over time
Attention span and ability to concentrate are diminished

Question 17

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

Answer 17

Sensory association cortex (somatosensory, visual and auditory)
Dorsomedial Nucleus of the thalamus
NOTE: lesion of the dorsomedial nucleus will have 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 as their is a deficit in attention to and awareness of one side of your visual field

Question 19

What effect do temporal cortex lesions have on memory?

Answer 19

Impaired short-term memory

They are effectively trapped in a 30 second window of memory (anterograde amnesia)

Question 20

Describe hemispheric specialisation.

Answer 20

Right hemisphere = creative + artistic

Left hemisphere = logical + scientific

Question 21

What is a callosotomy?

Answer 21

Cut of the corpus callosum. A palliative procedure used for the treatment of seizures
The corpus callosum is key for the 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 two 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

Transcranial Direct Current Stimulation (TDCS)
This changes the excitability of neurones but does NOT directly induce neuronal firing
Changes the rate they fire
Anode = increases neuronal excitability
Cathode = decreases neuronal 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
The tracer emits positrons, which are then detected by the receptors
It can be used in Parkinson’s disease to see the uptake of dopamine precursors by dopaminergic neurones in the striatum.

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

It is quite noisy – there is a lot of background activity
This is resolved by doing a trial of a large number of participants so that an average can be found
Once the average has been found, it can be deducted from the captured signal to see the underlying activity

Question 27

What is fMRI?

Answer 27

Function MRI
It detects changes in blood flow in the brain
It relies on the fact that blood flow in the brain and neuronal activity are coupled – more active parts of the brain require increased blood flow

Question 28

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

Answer 28

Amygdala

Rostral anterior cingulate cortex

Question 29

Give 3 examples of commissural fibres

Answer 29

corpus collosum, anterior commissure (in the basal forebrain), posterior commissure (connecting hippocampi)

Question 30

Describe the vertical orignisation of cells in the neocortex

Answer 30

Dense bands of neuorens with similar properties in columns. Forms the basis of topographic mapping.

Question 31

What is a potential application for TDCS?

Answer 31

TDCS could be used to reduce motion sickness by suppressing the area of the cortex associated with perceiving vestibular information

Question 32

What are the main differences between a primary cortex and an association cortex?

Answer 32

Primary:
function predictable​
organised topographically​
left-right symmetry

Association:
function less predictable​
not organised topographically​
left-right symmetry weak or absent