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

Some parts of cerebral cortex has 6 layers, some have 3 layers (less evolved). In humans however, most of the brain grey matter has 6 layers and so most of it is neocortex. Therefore, neocortex and cortex are used synonymously

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 e.g this is where upper motor neurons originate

Question 5

What does layer 1 mainly consist of?

Answer 5

Neuropil – a dense network of interwoven nerve fibres and their branches and synapses, together with glial filaments. THIS LAYER CONTAINS LITTLE CELL BODIES

Question 6

What type of neurone is found in layer 4?

Answer 6

Stellate neurones. These neurons receive input from thalamus. In the primary sensory cortices, these neurons receive input (3rd order neurons) from the thalamus, the major sensory relay from the periphery.

Question 7

What type of neurone is found in layer 5?

Answer 7

Pyramidal neurones (so Upper motor neurons are types of pyramidal neurones which originate from layer V of the cerebral cortex)

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)
Ventral Pathway – responsible for form and colour (WHAT)

Question 9

What is the role of the posterior parietal association cortex?

Answer 9

Its main functions are ATTENTION and VISUOSPATIAL perception.

Attention: If there is damage to posterior parietal cortex then you may get hemispatial neglect which is when you can see something but you only pay attention to one half of the object because one of your posterior parietal lobes is damaged.

Visuospatial perception: ability to process and interpret visual information about where objects are in space.

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

Question 10

What could injury of this part of the association cortex lead to?

Answer 10

• Disorientation (loss of direction/confusion)
• Inability to read a map or understand spatial relationships
• Apraxia (loss of ability to do things that the body can normally do)
• Hemispatial Neglect (deficit/neglect of awareness of one side of the field of vision)

Question 11

Define apraxia.

Answer 11

Inability to make skilled movements with accuracy

Question 12

What is the temporal lobe responsible for?

Answer 12

Language (part of Wernicke’s area is in temporal which is involved in understanding language. Temporal also has primary auditory cortex which is involved in processing the speech and vision)

Object Recognition (what pathway)

Memory (hippocampus is part of temporal)

Emotions (amygdala)

Question 13

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

Answer 13

AGNOSIA – cannot interpret sensory modalities. This may result in e.g not being able to recognise people’s faces- you can see their face but you cant interpret and process it.

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

This is a form of agnosia. Agnosia- cannot interpret sensory modalities. ProsopAGNOSIA specifically refers to prosopon= ‘face’
agnosia= ignorance

Question 15

What is the role of the frontal lobe?

Answer 15

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

Question 16

Frontal lobe injury consequences?

Answer 16

Characterised by a lack of ability to plan, behaviour becomes disorganised, attention span and concentration diminish, self-control is hugely impaired, change in personality

Question 17

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

Answer 17

Hemispatial neglect – they will only draw half of it

definition: a deficit in attention to and awareness of one side of the field of vision

Question 18

What effect do temporal cortex lesions have on memory?

Answer 18

Impaired short-term memory

They are effectively trapped in a 30 second window of memory

Question 19

Describe hemispheric specialisation and what is a another term for this phrase

Answer 19

Lateralisation. When some functions tend to be performed on one side of the brain over the other. E.g Broca and Wernickes area tend to be in left hemisphere

Question 20

What is a callosotomy?

Answer 20

A palliative procedure used for the treatment of seizures

The corpus callosum is key for the interhemispheric spread of epileptic activity

Question 21

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

Answer 21

Diffusion Tensor Imaging – Tractography

This imaging shows you all the tracts in the brain. Tracts are in white matter, cell bodies are in grey matter. This imaging shows u tracts so its white matter

Question 22

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

Answer 22

Transcranial Magnetic Stimulation (TMS)
 Magnetic field induces a current in the cortex
 This is method of focally stimulating different areas of the cortex and testing what each area is responsible for
Transcranial Direct Current Stimulation (TDCS)
 This changes the excitability of neurones but does NOT directly induce neuronal firing
 Anode = increases neuronal excitability
 Cathode = decreases neuronal excitability
 TDCS could be used to reduce motion sickness by suppressing the area of the cortex associated with perceiving vestibular information

Question 23

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

Answer 23

A radioactive tracer is attached to a molecule to locate areas of the brain where that molecule is being absorbed

It can be used in Parkinson’s disease to see the uptake of dopamine precursors by dopaminergic neurones

Question 24

What is the difference between MEGs and EEGs?

Answer 24

MEGs = magnetoencephalography – measures magnetic fields  
EEGs = electroencephalography – measures electric fields

Question 25

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

Answer 25

It is quite noisy – there is a lot of background noise which interferes with the signal

Resolved by repeating experiment on the participant and doing an average to make it more reliable.

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.

Question 26

What is fMRI?

Answer 26

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 27

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

Answer 27

Amygdala

Rostral anterior cingulate cortex

Question 28

Describe the horizontal and vertical organisation of the neocortex

Answer 28

Neocortex is arranged in layers (lamina structure) and columns

More dense vertical connections – the columnar organization is thought to be the basis for topographical organization

Neurons with similar properties are connected in the same column