Neurology 18 - Cerebral Cortex Flashcards
List the fibre types present in cerebral white matter
- Association fibres (connect areas within the same hemisphere)
- Commisural fibres (connect the left to the right hemisphere - corpus callosum, anterior and posterior commisural)
- Projection fibres (connect the cortex with lower brain structures, brain stem and spinal cord - corticospinal tract)
What is present in the different layers of the grey matter in the cortex?
Dorsal (outside)
- Layers 1 to 3 are mainly cortico-cortical connections (association). Layer 1 has few cells.
- Layer 4 is input from the thalamus
- Layers 5 and 6 are connections with subcortical, brainstem and spinal cord (output layers - Betz cells)
Ventral (inside)
How is the neocortex arranged?
- In layers (amina) and columns
- More dense vertical connections (basis for topographical organisation)
- Neurons with similar properties are connected in the same column
List the lobes of the neocortex
- Occipital
- Parietal
- Temporal
- Frontal
What is the function of the occipital lobe?
- Visual association cortex analyses different attributes of visual image in different places
- Form and colour analysed along ventral pathway, spatial and movement along dorsal pathway
- Lesions affect visual perception
List the functions of the parietal lobe
- Posterior parietal association cortex creates spatial map of body in surroundings, from multi-modality information
List the functions of the temporal lobe
- Language, object recognition, memory, emotion
List the functions of the frontal lobe
- Judgement, foresight, personality, appreciation of self in relation to world
Compare the primary and association cortices
Primary
- Function is predictable
- Organised topographically
- Left-right symmetry
Association
- Function less predictable
- Not organised topographically
- Left-right symmetry is weak or absent
List the primary cortices
- Primary motor cortex
- Primary somatosensory cortex
- Visual cortex
- Auditary cortex
- Gustatory cortex (taste)
- Olfactory cortex (smell)
List the association cortices and their functions
- Primary motor cortex + motor association area (skeletal muscle movement)
- Primary somatosensory cortex and sensory association area (sensory from skin, muscoskeletal, viscera and taste buds)
- Visual association cortex (vision)
- Auditory association area (hearing)
- Prefrontal association area (coordinates information from other association areas, and controls some behaviours)
What is the result of lesion in the visual posterior association cortex?
- Image attributes are processed separately (localisation in space is dorsal stream, and visual identification is ventral stream)
- Lesions result in inability to recognise familiar faces or learn new faces (prosopagnosia)
What is the result of frontal cortex lesions?
- Lack of planning
- Behaviour becomes disorganised
- Attention span and concentration diminish
- Self control is impaired
What is the result of parietal cortex lesions?
- Disorientation
- Inability to read maps or understand spatial relationships
- Apraxia
- Hemispatial neglect (don’t see one of the sides)
What is the result of lesions in the temporal cortex?
- Agnosia (inability to recognise things)
- Receptive aphasia (impairment of language)
What is seen in patients who have had a callosotomy?
- Split brain (can be born without a corpus callosum)
- Lateralised deficits in function
- Some processes are hemispheric
Explain hemispheric specialisation
The left hemisphere is language dominant, and the right is largely spatial processing
What is used to measure the effect of lesions?
- Structural imaging
- Tractography (diffusion tensor imaging)
What is the function of transcranial magnetic stimulation?
- Magnetic field induces an electric current in the cortex, causing neurons to fire
- Can be used to test whether a specific brain area is responsible for function
What is the effect of transcranial direct current stimulation?
- Changes local excitability of neurons
- Increases or decreases the firing rate, but does not directly induce neuronal firing
What could transcranial direct current stimulation be used to treat?
- Motion sickness
- By suppressing the area of the cortex associated with processing vestibular information
Describe the process of positron emission tomography (PET)
- Uses a radioactive tracer attached to a molecule to locate brain areas where that particular molecule is being absorbed in the brain
- Expensive, but with good spatial resolution and specificity
Describe the process of magnetoencephalography (MEG)
- Functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occuring naturally in the brain
- Uses sensitive magnetometrs
Describe the process of electroencephalography (EEG)
- An electrophysiological monitoring method to record electrical activity of the brain.
- Typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used in specific applications (intracortical EEG, for example to localise function during neurosurgery).
- Measures voltage fluctuations resulting from ionic current within the neurons of the brain
What can MEG and EEG not measure?
The activity of interior structures - they can only measure the surface activity of the brain
What is the issue with MEG/EEG?
- Noisy signals
- A large number of trials must be performed so an average can be used
Describe the process of functional magnetic resonance imaging
- Measures brain activity by detecting changes associated with blood flow
- Relies on the fact CBF and neuronal activation are coupled - more activity = more blood flow
How is optimism measured?
- Measure brain response to imagining positive and negative events in the future or past
- fMRI
