8a.) Higher Cortical Function Flashcards
How many layers does the cerebral cortex have?
6 layers containing cell bodies & dendrites (remember cortex is grey matter)
Most output from the cortex are via which neurones?
Pyramidal neurones (e.g. upper motor neurones int eh primary cortex are examples of pyramidal neurones)
**Shown in red on diagram
Outputs from motor cortex can be any of the 3 types of fibres in the CNS; remind yourself of these 3 types of fibres and state an example for each
- Assocition fibres: connecting nearby regions of cortex in same hemisphere e.g. arcuate fasciculus
- Comissure fibres: connect two hemispheres e.g. corpus callosum
- Projection fibres: going down to brainstem and/or cord e.g. upper motor neurones
Where do most inputs to the cortex come from? (2)
- Thalamus
- Other cortical areas
*NOTE: an important population of inputs areise from the reticular formation
Interneurones connect inputs and ouputs of the cortex in a complex way; what does this give rise to?
Emotion, behaviour, memory etc…
Can think of it as you are a sum of the inputs and outputs to the cortex
How do we know about lobe function in the human brain?
Most of what we know comes from studying lesions in natural experimetns (e.g. someone has a stroke in lobe x and we look at what deficits they have)
Pyramidal cells do not have dense dendritic trees; true or false?
FALSE; pyramidal cells do have dense dendritic trees allowing them to symapse with lots of interneurones
What is meant by cortical localisation?
Idea that different lobes of brain and different subdivisions have different functions
State 6 functions of frontal lobe. For each function, give a reason as to why it’s function is related to the frontal lobe and state what damage to the frontal lobe could result in (in terms of this function)
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Motor
- Primary motor cortex
- Frontal lobe damage can result in contralateral weakness
-
Expression of speech
- Broca’s area
- Damage to left frontal lobe (as speech is generally in left hemisphere) can result in expressive dysphasia
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Behavioural regulation/judgement:
- Prefrontal cortex
- Damage to frontal lobes can lead to (usually) impulsive, disinhibited behavioiurs e.g. sexual inappropriateness, aggression etc…
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Cognition:
- Prefrontal cortex
- Frontal lobe damage (particularly the right) can cause difficulty with tasks such as complex problem solving e.g. calculations
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Eye movements:
- Contain frontal eye fields
- Damage can cause problems with conjugate gaze and other eye movement disturbances (however, diplopia without other cortical features would suggest brainstem or cranil nerve problem)
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Continence:
- Contain cortical areas responsible for maintenance of continence (paracentral lobules)
- Damage can cause urinary incontinece
Alcohol can affect frontal lobes; true or false?
True- this is why people may display impulsive behaviour when drunk
*BUT remember that it is cerebellum that is highly sensitive to alcohol
State 4 (sort of 5) functions of the parietal lobes. For each function, give a reason as to why it’s function is related to the frontal lobe and state what damage to the frontal lobe could result in (in terms of this function)
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Sensory:
- Primary somatosensory cortex
- Damage may result in contralateral anaesthesia affecting all modalities
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Comprehension of speech:
- Contains part of Wernicke’s area
- Damage to left parietal lobe (as speech is generally in the left) can cause receptive dysphasia
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Body image & awareness of external environment:
- Seems to be involved in the acknowledgement that things (including the body) exist
- Damage to right parietal lobe can lead to neglect (right parietal lobe lesion would result in not acknowledging left half of space. This is because the right hemisphere acknowledges both. Whereas left hemisphere only acknowledges the right. So if lesion was on left neglect wouldn’t occur)
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Calculation & writing:
- Parietal lobes works with frontal lobe to perform tasks
- Damage to left parietal lobe can affect calculation ability (but remembe this could mean it is a frontal lobe lesion)
Not exaclty a function but remember that the superior optic radiations project through the parietal lobe
Explain why damage to the right parietal lobe would cause neglect but damage to the left parietal lobe would not cause neglect
Damage to right parietal lobe can lead to neglect (right parietal lobe lesion would result in not acknowledging left half of space). This is because the right hemisphere acknowledges both sides of space. Whereas left hemisphere only acknowledges the right side. So if lesion was in left parietal neglect wouldn’t occur as the right can do both.
State the 4 (sort of 5) functions of the temporal lobe. For each function, give a reason as to why it’s function is related to the frontal lobe and state what damage to the frontal lobe could result in (in terms of this function)
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Hearing:
- Primary auditory cortex sits on superior surface of temporal lobe (near Wernicke’s area)
- Damage can lead to complex effects on hearing (don’t need to know details- however, auditory hallucinations may be feature of temporal lobe lesions)
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Olfactation:
- Primary olfactory cortex sits on infero-medial aspect of temporal lobe
- Damage can lead to complex effects on smell (don’t need to know details however olfactory hallucinations may be a feature of temporal lobe lesions)
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Memory:
- Hippocampus is crucial for consolidating declarative memories
- Damage may lead to amnesia. Epilepsy in the temporallobe could trigger memories
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Emotion:
- Temproal lobes contain number of limbic structures like hippocampus & amygdala
- Effects of lesions are complex but lesions here may be related to pathogenesis of some psychiatric disorders
Not a function: but remember that inferior optic radiations project through temporal lobe
What limbic structure is the emotion centre of the brain?
Amygdala
*NOTE: limbic cortex= cingulate gyrus
Where abouts in temporal lobe do the:
- Primary olfactory cortex
- Primary auditory cortex
…. reside?
- Primary olfactory: inferomedial aspect
- Primary auditory: superior aspect
What do we mean by cerebral dominance?
Idea that some functions are represented more prominently in one hemisphere
State which hemisphere is usually dominant for:
- Language
- Mathematical/logical functions
- Body image/visuospatial awareness
- Emotion
- Musical ability
- Language & mathematical/logical functions= LEFT
- Body image, visuospatial awareness, emotion, musical ability= RIGHT
*This is situation in 95% of people
If someone presents with dysphasia, where is lesion likely to be?
Left hemisphere
What structure connects the two hemispheres?
Corpus callosum
Destruction of corpus callsoum can cause..? (2)
- Interesting syndromes e.g. Alien hand syndrome
- Subtle effects on language & processing
Describe alien hand syndrome
- Inability to control hand/hand seems to act on it’s own without conscious control
- Involuntary and autonomous activity of affected limbs
*Damage to corpus callosum can mean that the primary motor cortex and its motor neurones are no longer able to communicate with pre-motor cortical regions that would tell it what to do
If someone who has had an epileptic seizure describes it as de-ja-vu/triggered a memory where would you suspect the epilepsy to be?
Temporal lobe (as this has hippocampus for memory)
Which hemisphere is dominant in most people?
Left
***NOTE: think- this makes sense as most people are right handed. HOWEVER, in a left handed person the left hemisphere still does language etc….? Bizarre
Is the corpus callosum white or grey matter?
White
Who is the corpus callosum bigger in; males or females?
Females
Does damage to corpus callosum present with much of a deficit?
Generally not much of a deficit but you CAN get interesting syndromes such as alien hand
Describe how you could test if someone has neglect
- Draw a picture
- Get them to copy it
- They will copy right hand side
Or, draw circle and ask them to draw clock face on it and they will put all numbers on the right side
State the two areas involved in language and state where each is
- Broca’s area: inferolateral frontal lobe
- Wernicke’s area: parieto-temporal junction
Explain why the position of Broca’s area is ideal
It sits near to the mouth/pharynx area of primary motor cortex
State what each of the following areas is reponsible for:
- Broca’s area
- Wernicke’s area
- Broca’s= production of speech
- Wernicke’s= comprehension (understanding) of speech
Damage to Broca’s area leads to what symptom?
- Staccato speech (also known as Broca’s/expressive dysphsia)
- Patient understands what was said to them but strugges to produce the words
Explain why the position of Wernicke’s area is ideal
Sits near primary auditory cortex in the temporal lobe
Damage to Wernicke’s area can lead to what symptom?
- Wernicke’s/receptive aphasia
- Patients do not understand what was said to them hence they have fluent, but nonsensical speech
Large occlusions of which artery can cuse dense/global aphasia where both Broca’s and Wernicke’s area are destroyed leading to virtually no verbal language function?
Middle cerebral artery
(as this supplies lateral parts of frontal and parietal lobes where Broca’s and Wernickes are found)
What structure connects Broca’s area and Wernicke’s area?
Arcuate faciculus
What could damage to the arcuate fasciculus result in?
Inability to repeat heard words
Describe the pathway for repeating a heard word
- Primary auditory cortex
- Broca’s
- Arcuate fasciculus
- Wernicke’s
- Primary motor cortex
Describe the pathway for speaking a written word
- Primary visual cortex
- Broca’s area
- Arcuate fasciculus
- Wernicke’s area
- Primary motor cortex
Describe the pathway for speaking a thought
- Inputs from all over cortex
- Broca’s area
- Arcuate fasciculus
- Wernicke’s area
- Primary motor cortex
Where are memories stored?
Thought to be realtively distributed throughout large areas of brain
State and describe the two types of memory
Declarative/explicit:
- Factual information
Non-declarative/implicit:
- Motor skills & emotion
State where each of the following types of memory tends to be stored:
- Declarative/explicit
- Non-declarative/implicit
- Declarative: cerebral cortex
- Non-declarative: subcortical structures (e.g. basal ganglia & cerebellum)
Describe the followinig:
- Short term memory
- Long term memory
- Short: stored for seconds to minutes as a ‘reverberation’ or ‘echo’ in cortical circuits
- Long: stored for very long periods of time (up to a lifetime) in cerebral cortex, cerebelum etc…. FOLLOWING consolidation
What do we mean by consolidation?
Converting short term memories into long term memories (via long term potentiation)
State, and describe, 3 factors influencing consolidation
- Emotional context: if an event has a strong emotional content then it tends to be remembered better
- Rehersal: more you repeat, more likely to be consolidated
- Association: if you can associate a piece of knowledge with something you already know it tends to be remembered more easily
Which region of cortex helps to consolidate declarative memories?
hippocampus
Where is the hippocampus?
Deep in temporal lobe- rolled medial edge of temporal lobe
Why is the hippocampus good at associating stimuli?
Because it has multimodal inputs from many brain systems
Describe long term potentiation
Key molecular mechanism of memory consolidation:
- Causes changes in glutamate receptors in synapses leading to synaptic strengthening
- New physical connections cn also form between neurones to further strengthen connections (axonal sprouting)
Hippocampus has a role as an oscillator; what does this mean?
Facilitates consolidation of memories in the cortex via it’s output pathways (primarily the fornix -> mammillary bodies -> thalamus -> cortex)
