Higher Cortical Function Flashcards
Describe the fine structure of the cerebral cortex
Arranged as 6 layers containing cell bodies and dendrites (i.e. cortex is grey mater)
Most outputs from the cortex are the axons of pyramidal neurones (e.g. upper motor neurones in the primary motor cortex are pyramidal neurones)
Pyramidal neurones have extensive dendrites, each covered in spines which represent a synapse
What are the outputs from the cortex
Most outputs from the cortex are the axons of pyramidal neurones (e.g. upper motor neurones in the primary motor cortex are pyramidal neurones)
•Outputs can be projection fibres going down to brainstem and cord (e.g. upper motor neurones)
•Outputs can be commissural fibres going between hemispheres (e.g. corpus callosum)
•Outputs can be association fibres connecting nearby regions of cortex in the same hemisphere (e.g. arcuate fasciculus)
Describe the inputs to the cortex
Most inputs are from thalamus and other cortical areas
•An important population of inputs arise from the reticular formation, maintaining cortical activation (consciousness)
Interneurones connect inputs and outputs in a complex way, giving rise to behaviour, emotion, memory etc
How is function localised in the brain lobes
Localisation of function – brain lobes
The cortex is divided into defined areas with (probably) specific roles. Most of what we know about lobe function in humans derives from lesion studies resulting from natural experiments (e.g. the effect of strokes). There are many caveats to the interpretation of such studies, but we know enough to have a decent guess at which lobe may be involved
What are the fucntions of the frontal lobe
•Frontal lobe functions, with effects of cortical damage
oMotor
- Primary motor cortex and associated areas are here
- Frontal lobe damage can result in contralateral weakness
oExpression of speech (usually left hemisphere)
- Broca’s area is here
- Damage to left frontal lobe can result in expressive dysphasiaoBehavioural regulation / judgement
- Prefrontal cortex etc. is here
- Damage to frontal lobes can lead to (usually) impulsive, disinhibited behaviours e.g. sexual inappropriateness, aggression
- Cghildren are an example of under developed fronal lobes - they ae one of the last areas to develop
oCognition
- Prefrontal cortex etc.
- Frontal lobe damage (particularly the right) can cause difficulty with tasks such as complex problem solving, including calculation
oEye movements
- Contain the frontal eye fields
- Damage can cause problems with conjugate gaze and other eye movement disturbances (however, diplopia without other cortical features would suggest brainstem/cranial nerve problem)
oContinence
- Contain cortical areas responsible for maintenance of continence (e.g. paracentral lobules)
- Damage can cause urinary incontinen
What are the parietal lobe functions
Parietal lobe functions, with effects of cortical damage
oSensory
- Contains primary sensory cortex and associated areas
- Damage might result in contralateral anaesthesia affecting all modalities (modalities converge at the cortex)
oComprehension of speech
- Contains part of Wernicke’s area
- Damage to left parietal lobe can cause a receptive dysphasia
oBody image and awareness of external environment
- Seems to be involved with acknowledgement that things (including the body) exist
- Damage to right parietal lobe can lead to neglect.
oCalculation and writing
- Works with frontal lobe to perform these tasks
- Damage to left parietal lobe can affect calculation ability (but maybe also frontal lobe)
oAlthough not a cortical function, remember that the superior optic radiation projects through the parietal lobe
- Damage here can cause a contralateral inferior homonymous quadrantanopia
What are the temporal lobe functions?
Temporal lobe functions, with effects of cortical damage
oHearing
- Primary auditory cortex sits on superior surface of temporal lobe, near to Wernicke’s area
- Damage can lead to a number of complex effects on hearing which are not the remit of the unit. Auditory hallucinations may be a feature of temporal lobe lesions
oOlfaction
- Primary olfactory cortex sits on the infero-medial aspect of the temporal lobe
- Damage can lead to a number of complex effects on smell which are not the remit of the unit. Olfactory hallucinations may be a feature of temporal lobe lesions
oMemory
- The hippocampus is a crucial structure for consolidating declarative memories
- Damage may lead to amnesia (but remember that there are two hippocampi, one in each temporal lobe). Also, some pathologies such as temporal lobe epilepsy can trigger memories, leading to a feeling of deja vu
oEmotion
- Temporal lobes contain a number of limbic system structures such as the hippocampus and amygdala
- Effects of lesions are complex, but may be related to pathogenesis of some psychiatric disorders
oAlthough not a cortical function, remember that the inferior optic radiation projects through the temporal lobe
- Damage here can cause a contralateral superior homonymous quadrantanopia
What is cerebral dominance?
Cerebral ‘dominance’ oSome functions are represented more prominently in one hemisphere
- In 95% of people, the left hemisphere is dominant for language and mathematical/logical functions
- In 95% of people the left hemisphere is dominant for body image, visuospatial awareness, emotion and musical ability
oKnowledge of cerebral dominance allows us to predict the effects of lobe lesions (e.g. a dysphasia is likely to have arisen from left hemisphere damage)
What is hemispatial neglect
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What is the corpus callosum
The corpus callosum allows the two hemispheres to communicate with one another, meaning we can be thought of as an ‘average’ of the two hemispheres
- Destruction of the corpus callosum can cause some interesting deficits such as alien hand syndrome and subtle effects on language processing
What is Broca’s area?
oBroca’s area
- In the infero-lateral frontal lobe
- Sits near to mouth/pharynx area of primary motor cortex
- Responsible for the production of speech
- Damage can cause staccato speech, where the patient still understands what is being said to them (Broca’s / expressive dysphasia
What is Wernicke’s area
oWernicke’s area
- At the parieto-temporal junction
- Sits near to primary auditory cortex in temporal lobe
- Responsible for the comprehension of speech
- Damage can cause fluent, nonsensical speech where the patient does not appear to understand what is being said to them (Broca’s / receptive dysphasia)
What connects Broca’s and Wernicke’s areas
Broca’s and Wernicke’s areas are connected by the arcuate fasciculus
- Damage to this white matter pathway can cause the inability to repeat heard words. Thought to be unidirectional W->B
How can MCA infarcts affect B and W area
Large middle cerebral artery infarcts can cause am dense / global aphasia where both areas are destroyed leading to virtually no verbal language function
Wjere are memories stored?
Memories are believed to be stored across wide areas of the brain
