Organisation of the Cerebral Cortex Flashcards
What are the three types of fibre that make up white matter?
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)
How many layers of grey matter are there?
3-6 (they are usually numbered by roman numerals)
What is the neocortex?
A part of the cerebral cortex concerned with sight and 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 and spinal cord
What does layer 1 mainly consist of?
Neuropil – 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
What type of neurone is found in layer 4?
Stellate neurones
What type of neurone is found in layer 5?
Pyramidal neurones
What are the two parts of the visual association cortex and what are they responsible for?
Dorsal Pathway – responsible for interpretation of spatial relationships and movements
Ventral Pathway – responsible for form and colour
What is the role of the posterior parietal association cortex?
It creates a SPATIAL MAP of the body in its surroundings from multi-modality information
What could injury of 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 two main consequences of injury to the temporal lobe?
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
What are the consequences of visual association cortex lesions?
Prosopagnosia – inability to recognise faces
What is the role of the frontal lobe?
Executive functions e.g. planning, judgement, foresight, personality
What are the consequences of prefrontal damage?
Change in personality
Inappropriate behaviour
Lack of ability to remember and relate things over time
Attention span and ability to concentrate are diminished
What two areas does the prefrontal cortex receive massive inputs from?
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
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
They are effectively trapped in a 30 second 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
The corpus callosum is key for the 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 two types of brain stimulation testing and what it can be used for.
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
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
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
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?
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
What is fMRI?
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
Which areas of the brain become more active when participants imagine positive events?
Amygdala
Rostral anterior cingulate cortex
Features of primary cortices
Functionally predictable
Organised topographically
Left-right symmetry
Features of association cortices
Functionally less predictable
Not organised topographically
Left right symmetry weak or absent
Effects of damage to parietal cortex?
Association cortex important for spatial awareness so damage leads to disorientation, inability to read maps and understanding of spatial awareness
