Neuro 13: Cerebral cortex

Question 1

State grey and white matter distribution in cortex

Answer 1

Grey matter outside and white matter inside

Question 2

State the 3 types of fibres of the white matter

Answer 2

Association fibres: connect areas within the same hemisphere (=local cirtcuity)

Commissural fibres: connect left hemisphere to right hemisphere (for lateralised functions).. corps callosum, anterior commisure (base of forebrain), posterior commisure (join the 2 hypocampi)

Projection fibres: connect cortex with lower brain structures (e.g. thalamus), brain stem and spinal cord…. e.g. corticospinal tract

Question 3

How many layers of the neocortex

Answer 3

6

some old areas near hypocampus are 3 layers

Question 4

What is in each layer of cortex including cell types

Answer 4

1: mostly association fibres (acellular).. =neuropil (any area in the nervous system composed of mostly unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies)

2 and 3: contain smaller PYRAMIDAL NEURONS

layers 1-3 about cortio-cotical connections

4 input from the thalamus (input). STELLATE NEURONS

5-6: projections to subcortical, brain stem and spinal cord (e.g. in layer V pyramidal cells with large cell bodies)

Question 5

How else is the cortex arrangd other than laminae

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 structure is found by retracting the frontal, temporal and patietal lobe

Answer 6

insular cortex ( involved in consciousness and play a role in diverse functions usually linked to emotion or the regulation of the body’s homeostasis)

Question 7

Layer IV of the cortex

Answer 7

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.

Question 8

Where do taste fibres go to

Answer 8

Solitary nucleus… input from faical, glossopharyngeal and vagus…. located in the MEDULLA

Question 9

Which side of brain involved in languae

Answer 9

left side (broca’s and wernickes)

BROCA’S- dominant frontal lobe (so usually left)…. motor speech production (dysarthria)

WERNICKE’S- dominant temporal lobe (so usually left)… understanding language (aphasia)

Question 10

What is the assocation cortices, and what is the extend of their topographic organisation

Answer 10

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

Question 11

Outline the 2 streams from the occipital lobe

Answer 11

dorsal stream (where)=spatial relationships & movement 
 and 
ventral (what) stream=form & colour analyzed incl. recognition

Question 12

What is prosopagnosia and how does it occur

Answer 12

Lesions of the visual posterior association area (fusiform gyrus) can result in the inability to recognize familiar faces or learn new faces—a deficit called prosopagnosia (aka face blindness).

Fusiform gyrus part of the ventral pathway

Question 13

Frontal cortex lesion presentation

Answer 13

Characterised by a lack of planning, behaviour becomes disorganised, attention span and concentration diminish, self-control is hugely impaired

(think pre-motor cortex involved in planning for externally cued movements i.e. reaching out for an apple, and supplementary motor area responsible for planning complex movements/SEQUENCES…. could be disrupted leading to these symptoms)

Question 14

Lesion of parietal lobe

Answer 14

posterior parietal association cortex creates a spatial map of the body in surroundings, from multi-modality information (sensory areas anterior give info and occipial behind via the dorsal flow?)

injury may cause disorientation, inability to read maps or understand spatial relationships, apraxia, hemispatial neglect

Question 15

Temporal cortex lesions

Answer 15

Language, object recognition, memory, emotion. Injury leads to agnosia (damage to ventral stream), receptive aphasia

Question 16

Evidence for hemispheric specialisation

Answer 16

Patients who have had a callosotomy (split brain) have lateralised deficits in function

Question 17

What is TMS and what is its use

Answer 17

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

i.e. when you apply a magnetic field to the area, does it still work or is it interrupted (michael mosely video)

Question 18

What is TDCS

Answer 18

Transcranial direct current stimulation-

Changes the local excitability of neurons, increasing or decreasing the firing rate
(NB, does not directly induce neuronal firing)….

The anode will INCREASE excitability
The cathode will DECREASE excitability

Question 19

What is PET imaging

Answer 19

PET (Positron emission tomography) 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.

It is an expensive process but has good spatial resolution and specificity in terms of the underlying biology (i.e. it is the only way to identify brain regions absorbing particular substances).

Question 20

Differentiate MEG and EEG

Answer 20

MEG: measures magnetic fields…. mapping brain activity by recordingmagnetic fieldsproduced by electrical currents occurring naturally in thebrain using MAGNETOMETERS

EEG: measures electric fields. Non invasive, electrodes on scalp (but invasive electrodes used in intracortical EEG to localise function during neurosurgery). EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain

‘noisy’ so lots need to be taken so average can be used

Question 21

What does fMRI look at

Answer 21

Functional magnetic resonance imaging (fMRI)

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
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Question 22

What could be used to reduce motion sickness

Answer 22

TDCS could be used to reduce motion sickness by suppressing the area of the cortex associated with processing vestibular information (increase inhibition via the cathode)

Question 23

Outline hemispheric specialisation

Answer 23

Right Hemisphere = artistic + creative

Left Hemisphere = logical + scientific

Question 24

What is agnosia

Answer 24

Agnosia = disorder of the brain whereby the patient cannot interpret sensations correctly although the sense organs and nerves conducting sensation to the brain are functioning normally

E.g. auditory agnosia = patient can hear but can’t interpret sounds

Tactile agnosia = retains normal sensation in the hands but cannot recognise three dimensional objects by touch alone

Visual agnosia = patient can see but cannot interpret symbols, including letters

Question 25

Damage to which lobe may cause apraxia

Answer 25

Posterior parietal association cortex creates a spatial map of the body in its surroundings from multi-modality information

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

DEFINITION OF APRAXIA = inability to make skilled movements with accuracy

Question 26

How can optimism be measured

Answer 26

When participants imagined positive events in the future or the past, the amygdala and rostral anterior cingulate cortex were MORE ACTIVE than when they imagined negative events

Question 27

What is diffuse tensor imaging

Answer 27

aka Tractography

MRI based modality

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 be used to estimate the location and connections between different white matter pathways.

This way, you can build up a fibre network of the brain

Question 28

Outline hemispheric specialisation test

Answer 28

If you show somebody with a collosotomy an word on their right, the fibres can cross over the intact optic chiasm to the left side of the brain. They will say what the word is

If you show them the word on the left, then because most fibres cross over to the right, and there is no commuinication between the right and the left becasue of the collosotomy, they will say they saw nothing, but they can draw what they saw (right side is artistic and creative)

Question 29

What would PET imaging show in parkinsons

Answer 29

You use flouro-DOPA

to label dopaminergic terminals in
the striatum

In PD (right), there is profound loss in the posterolateral putamen with relative preservation of the caudate.