Cerebral cortex Flashcards
What is the white matter of the brain and where is it found?
The inside - axons and connections
What is the grey matter of the brain and where is it found?
Surface of the brain - has cell bodies
What are the 3 types of fibres in the white matter?
- association fibres
- commisural fibres
- projection fibres
What are association, commissural and projection fibres?
- Association fibres: connect areas within the same hemisphere – local circuitry e.g. joining gyri next to eachother
- Commissural fibres: connect left hemisphere to right hemisphere and integrate info between different association areas
- Projection fibres: connect cortex with lower brain structures (e.g. thalamus), brain stem and spinal cord. They are long projection pathways e.g. motor pathways
What is the neocortex and the archicortex and how many layers do they have?
Neocortex - most of cortex
Archicortex - around hippocampus
N - 6 layer structure
A - 3 cortical layers
What are the different layers of the neocortex?
- Layer I contains mainly neurophils
- The generally smaller pyramidal neurons in layers II and III have primarily corticocortical connections - Cortical layer IV is typically 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
- Layer V, and to a lesser degree layer VI, contain pyramidal neurons whose axons typically leave the cortex (output)
How does the neocortex vary between cortical areas, give an example?
- Varies slightly in its microscopic detail between different cortical areas
- For example, the primary visual cortex has an extra layer of wet matter inserted within the 6-layer structure
- This is why we call it the striate cortex (it has an extra layer of white matter)
How else is the cortex arranged?
- Cortical columns
- They have dense vertical connections
- Neurones with similar properties are connected in the same column
- The columns are the basis for topographical organisation
What is the neocortex arranged into?
Different lobes
What are primary and association cortices?
Primary cortices: function is predictable, organised topographically, left-right symmetry
Association cortices: function less predictable, not organised topographically, left-right symmetry weak/absent
What are the different lobes?
occipital, parietal, temporal and frontal
What is the role of the primary visual cortex and which lobe is it in?
- occipital lobe
- processing vision
What does the visual association cortex do?
Analyses different attributes of visual image in different places. The form & colour is analysed along the ventral pathway; spatial relationships & movement along dorsal pathway. Lesions affect specific aspects of visual perception.
What is the role of the primary somatosensory cortex and where is it?
- Post-central gyrus in the parietal lobe
- Processes sensory information
What does the posterior parietal association cortex do?
Injury of parietal lobe leads to?
Creates spatial map of body in surroundings, from multi-modality information. Injury may cause disorientation, inability to read map or understand spatial relationships, apraxia, hemispatial neglect.
What is apraxia?
Motor disorder in which the individual has difficulty with the motor planning to perform tasks or movements
Where is the primary auditory cortex do and what does the temporal lobe do?
Injury leads to?
- In the superior temporal gyrus in the temporal lobe
- Processes language, object recognition, memory, emotion
- Injury leads to agnosia, receptive aphasia (Wernicke’s)
What is agnosia?
Inability to process sensory information. Often there is a loss of ability to recognize objects, sounds, shapes, or smells
Where is the primary motor cortex?
Part of the pre-central gyrus in the frontal lobe
What is the role of the frontal lobe?
Injury leads to?
Judgement, foresight, personality, appreciation of self in relation to world. Injury leads to deficits in planning and inappropriate behaviour
Are Broca’s and Wernicke’s area on right and left side?
No, lateralised to the left
Where are Broca’s and Wernicke’s area?
Broca’s area - inferior frontal lobe
Wernicke’s area - junction between parietal/temporal
What are some ways of measuring brain function?
PET
fMRI
EEG
Light micrcoscopy
What are the two main visual processing pathways in the primary visual cortex?
The dorsal steam WHERE – spatial relationship
The ventral stream WHAT – colour, form
What are some visual association pathways?
They connect to other parts of the brain and pick out individual attributes of images. One part detects motion.
What can lesions of the visual posterior association area lead to?
The inability to recognize familiar faces or learn new faces—a deficit called prosopagnosia (aka face blindness)
What happens in the visual association cortex?
Image attributes are processed separately
What are frontal cortex lesions characterised by?
A lack of planning, behaviour becomes disorganised, attention span and concentration diminish and self-control is hugely impaired (disinhibition
What are parietal cortex lesions characterised by?
- Disorientation, inability to read maps or understand spatial relationships, apraxia and hemispatial neglect (when patient draws something, they only draw half of it)
- Patients lose their visual-spatial integration
What does the parietal lobe (primary parietal association cortex) do?
- Creates a spatial map of the body in surroundings, from multi-modality information
- Integrates memory and where things are in space
What is the role of the temporal lobe?
What do lesions result in?
- language, object recognition, memory and emotion
- agnosia and receptive aphasia (difficulty understanding written and spoken language)
How can temporal cortex lesions be treated?
How is this different to what was done in the past?
- Removal of the damaged portion of the temporal lobe
- Before the solution was to do a bilateral temporalobectomy which resulted in dense anterograde amnesia
What is a callosotomy?
corpus callosum is cut (for epilepsy)
What are the role of the right and left hemispheres?
The left hemisphere is language dominant, the right hemisphere is largely spatial processing.
Can people be born without corpus callosum’s and how are they different to those who had a callosotomy?
- Someone born without a corpus callosum will have automatic compensatory mechanisms
- However, they will still have subtle psychological deficits
- In patients who have this due to surgical procedures, this is often more obvious as they have gone from normal to impaired
What are some experiments done in split brain research?
- A word is flashed briefly to the right field – you ask the patient what they saw
- They will be able to do this, because the left hemisphere is dominant for verbal processing
- If you flash the word briefly to the left field, the patient doesn’t can’t say what they see
- However, they will be able to draw what the word say
What is diffusion tensor imaging?
- A MR modality that looks for alignment of water molecules, and coincident activity
- Coincident alignment is taken to mean fibre connectivity
- This way, you can build up a fibre network of the brain
- We can use DTI in brain tumour patients to show break down of such connections
- DTI gives us more information about interruption to specific intracortical circuitry
What is 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.
What is transcranial direct current stimulation?
- Changes the local excitability of neurons, increasing or decreasing the firing rate
- This does not directly induce neuronal firing , however, it changes the threshold for decreasing/increasing the firing rate
- Affects the resting voltage of the neuronal membrane to stimulate a neuron’s activity in a desired direction
What are PET scans?
- Work by detecting the radiation given off by a radiotracer (similar to GLUCOSE) as it collects in different parts of your body
- This can be used to identify any abnormalities
- E.g
a high conc can identify cancerous cells because cancer cells use glucose at a much faster rate than normal cells
Why is PET mainly used in research?
expensive
How do MEG and EEGs work?
MEG: measures magnetic fields – involved a big machine
EEG: measures electric fields – involved lots of electrodes
What are event-related potentials?
- brain activity related to a stimulus
- lots of background noise so repeated and layered to remove noise
What is an fMRI?
- This is usually about monitoring blood flow and glucose metabolism
- Glucose use is probably related to functional activity of the brain
- Where there is more glucose and more blood flow, there is probably higher activity
How can we measure optimism?
- Measure the brain response to imagining positive and negative events in the future or the past
- 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
