Organisation of the Cerebral Cortex Flashcards
What are the 3 types of fibre that make up white matter?
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)
How many layers of grey matter are there?
3-6 (numbered by roman numerals)
What is the neocortex?
Part of the cerebral cortex concerned with sight + hearing in mammals, regarded as the most recently evolved part of the cortex
Describe the different connections of the 6 layers of grey matter.
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem + spinal cord
What does layer 1 mainly consist of?
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
What type of neurone is found in layer 4?
Stellate neurones
What type of neurone is found in layer 5?
Pyramidal neurones (Betz cells)
What are the 2 parts of the visual association cortex and what are they responsible for?
Dorsal Pathway: responsible for interpretation of spatial relationships + movements (Where)
Ventral Pathway: responsible for form + colour (What)
What is the role of the posterior parietal association cortex?
Creates a SPATIAL MAP of the body in its surroundings from multi-modality information
What could injury to the posterior parietal association cortex lead to?
Disorientation
Inability to read a map or understand spatial relationships
Apraxia
Hemispatial Neglect
Define apraxia.
Inability to make skilled movements with accuracy
What is the temporal association cortex responsible for?
Language
Object Recognition
Memory
Emotions
What are the 2 main consequences of injury to the temporal lobe?
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
What are the consequences of lesions of the visual posterior association area (fusiform gyrus)?
Prosopagnosia: inability to recognise faces
What is the role of the frontal lobe?
Executive functions e.g. judgement, foresight, personality, appreciation of self in relation to world
What are 4 consequences of a prefrontal lobotomy? Where may this be seen clinically?
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
What 2 areas does the prefrontal cortex receive massive inputs from?
Sensory association cortex (somatosensory, visual + auditory)
Dorsomedial Nucleus of the thalamus
(lesion of the dorsomedial nucleus has similar consequences to prefrontal lobotomy)
If you give someone with a unilateral parietal lobe lesion something to draw, what will you expect him or her to do?
Hemispatial neglect: they will only draw half of it
What effect do temporal cortex lesions have on memory?
Impaired short-term memory
Effectively trapped in a 30s window of memory
Describe hemispheric specialisation.
Right hemisphere = creative + artistic
Left hemisphere = logical + scientific
What is a callosotomy?
A palliative procedure used for the treatment of seizures- cuts through corpus callosum
Thus prevents interhemispheric spread of epileptic activity
State a type of imaging that uses the movement of water molecules in the brain to infer the underlying structure of white matter.
Diffusion Tensor Imaging (Tractography)
State 2 types of brain stimulation testing and what it can be used for.
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
Describe and explain how PET scans work. What can it be used for?
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
What is the difference between MEGs and EEGs?
MEGs = magnetoencephalography: measures magnetic fields EEGs = electroencephalography: measures electric fields
What is a major problem with MEGs and EEGs and how is this resolved?
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
What is fMRI?
What does it detect?
How?
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
Which 2 areas of the brain become more active when participants imagine positive events?
Amygdala
Rostral anterior cingulate cortex
Describe the columnar arrangement of cortical layers
Neocortex is arranged in layers + columns
Neurones with similar properties are connected in the same column
What characterises primary cortices? (Function, organisation)
Function predictable
Organised topographically
Left-right symmetry
What characterises association cortices? (function, organisation)
Function less predictable
Not organised topographically
Left-right symmetry weak or absent
A patient with a callosotomy is shown a word on RHS of view. On being asked what he saw, what would be say?
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
A patient with a callosotomy is shown a word on LHS of view. On being asked what he saw, what would be say?
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.
What could TDCS potentially be used for?
To reduce motion sickness by suppressing the area of the cortex associated with perceiving vestibular information
