Cortical Organisation and Function Flashcards
How is the cerebral cortex organised microscopically?
Layers and columns
What is cytoarchitecture?
Cell size, spacing or packing density and
layers
What neurologist identified 52 regions based on cytoarchitecture?
Brodmann
What are the functions of the frontal lobe?
- Regulating and initiating motor function
- Language
- Cognitive functions (executive function
[e.g. planning]) - Attention
- Memory
What are the functions of the parietal lobe?
- Sensation - touch, pain
- Sensory aspects of language
- Spatial orientation and self-perception
What are the functions of the occipital lobe?
- Processing visual information
What are the functions of the temporal lobe?
- Processing auditory information
- Emotions
- Memories
What are the functions of the limbic lobe?
- Learning
- Memory
- Emotion
- Motivation
- Reward
What does the limbic lobe include?
- Amygdala
- Hippocampus
- Mamillary body
- Cingulate gyrus
What are the functions of the insular cortex?
- Visceral sensations
- Autonomic control
- Interoception
- Auditory processing
- Visual-vestibular integration
Where can the insular cortex?
Deep within the lateral fissure
What is grey matter?
Neuronal cell bodies and glial cells
What is white matter?
Myelinated neuronal axons arranged in tracts
What do white matter tracts do?
Connect cortical areas
What are 3 types of white matter tracts?
- Association fibres
- Commissural fibres
- Projection fibres
What do association fibres do?
Connect areas within the same hemisphere
What fibres connect areas within the same hemisphere?
Association fibres
What do commissural fibres do?
Connect homologous structure in left and right hemispheres
What fibres connect homologous structure in left and right hemispheres?
Commissural fibres
What do projection fibres do?
Connect cortex with lower brain structures (e.g. thalamus, brain stem and spinal cord)
What fibres connect cortex with lower brain structures (e.g. thalamus, brain stem and spinal cord)?
Projection fibres
What types of association fibres are there?
- Superior Longitudinal Fasciculus
- Arcuate Fasciculus
- Inferior Longitudinal Fasciculus
- Uncinate Fasciculus
What association fibres are long?
- Superior Longitudinal Fasciculus
2. Arcuate Fasciculus
What association fibres are short?
- Inferior Longitudinal Fasciculus
2. Uncinate Fasciculus
What does the Superior Longitudinal Fasciculus connect?
Connects frontal and occipital lobes
What does the Arcuate Fasciculus connect?
Connects frontal and temporal lobes
What does the Inferior Longitudinal Fasciculus connect?
Connects temporal and occipital lobes
What does the Uncinate Fasciculus connect?
Connects anterior frontal and temporal lobes
What connects frontal and occipital lobes?
Superior Longitudinal Fasciculus
What connects frontal and temporal lobes?
Arcuate Fasciculus
What connects temporal and occipital lobes?
Inferior Longitudinal Fasciculus
What connects anterior frontal and temporal lobes?
Uncinate Fasciculus
What types of commissural fibres are there?
- Corpus callosum
2. Anterior commissure
What types of projection fibres are there?
- Afferent
2. Efferent
What do projection fibres deep to the cortex radiate as?
Corona radiata
Where do projection fibres converge through?
Through internal capsule between thalamus and basal ganglia
Where are the motor areas found?
Frontal lobe
What does the primary motor area do?
- Controls fine, discrete, precise voluntary
movements. - Provides descending signals to execute
movements.
What does the supplementary motor area do?
Involved in planning complex movements (e.g.
internally cued, e.g. speech)
What does the premotor area do?
Involved in planning movements (e.g. externally cued)
Where is the somatosensory area located?
Parietal lobe
What does the primary somatosensory area do?
Processes somatic sensations arising from receptors in the body.
What does the somatosensory association area do?
- Interpret significance of sensory information, e.g. recognizing an object placed in the hand.
- Awareness of self and awareness of personal space
What somatic sensations arise from receptors in the body?
- Fine touch
- Vibration
- Two-point discrimination
- Proprioception
- Pain
- Temperature
Where is the visual area located?
Occipital lobe
What does the primary visual area do?
Processes visual stimuli
What does the visual association area do?
Gives meaning and interpretation of visual input
Where is the auditory area located?
Temporal lobe
What does the primary auditory area do?
Processes auditory stimuli
What does the auditory association area do?
Gives meaning and interpretation of auditory input
What does the prefrontal cortex do?
- Attention
- Adjusting social behaviour
- Planning
- Personality expression
- Decision making
What does Broca’s area ddo?
Production of language
What does Wernicke’s area do?
Understanding of language
What do frontal lobe lesions cause?
- Changes in personality
2. Inappropriate behaviour
What do parietal lesions cause?
- Contralateral neglect
- Lack of awareness of self on left side (if lesion on right hemisphere)
- Lack of awareness of left side of extrapersonal space
What do temporal lesions cause?
Agnosia
What is it called if you cannot form new memories?
Anterograde amnesia
What is anterograde amnesia?
Can not form new memories
What is agnosia?
Inability to recognise
What is the inability to recognise called?
Agnosia
What white motor tract connects Broca’s area and Wernicke’s area?
Arcuate fasciculus
What does a lesion to Broca’s area cause?
Expressive aphasia
What does a lesion to Wernicke’s area cause?
Receptive aphasia
What is expressive aphasia?
Poor production of speech, comprehension intact
What lesion causes expressive aphasia?
Broca’s area
What is receptive aphasia?
Poor comprehension of speech, production is fine
What lesion causes receptive aphasia?
Wernicke’s area
What lesion leaves speech comprehension intact?
Broca’s area
What lesion leaves speech production intact?
Wernicke’s area
What does a lesion in the primary visual cortex cause?
Blindness in the corresponding part of the visual field
What does a lesion in the visual association area cause?
Deficits in interpretation of visual information e.g. prosopagnosia
What is prosopagnosia?
Inability to recognise familiar faces or learn new faces (face blindness)
What is inability to recognise familiar faces or
learn new faces (face blindness) called?
Prosopagnosia
What imaging techniques can assess cortical function?
- PET - positron emission tomography
2. fMRI - function magnetic resonance imaging
What does PET measure?
Blood flow directly to a brain region
What does fMRI measure?
Amount of blood oxygen in a brain region
What encephalography techniques can assess cortical function?
- EEG - electroencephalography
2. MEG - magnetoencephalography
What does EEG measure?
Measures electrical signals produced by the the brain
What does MEG measure?
Measures magnetic signals produced by the brain
Describe the localisation of function for primary cortices?
- Function predictable
- Organised topographically
- Symmetry between left and right
Describe the localisation of function for secondary cortices?
- Function less predictable
- Not organise topographically
- Left-right symmetry weak/absent
How could encephalography be used to access cortical function?
- Visual evoked potentials
- Event-related potentials/evoked-potentials
- Somatosensory evoked potentials
How could somatosensory evoked potentials in encephalography be used to access cortical function?
Series of waves that reflect sequential activation of neural structures along the somatosensory pathways.
What brain stimulation be used to assess cortical function?
- TMS - transcranial magnetic stimulation
2. tDCS - transcranial direct current stimulation
What does TMS do?
Uses electromagnetic induction to stimulate neurones
-> assess the functional integrity of neural circuits
What can TMS assess in cortical function?
- Investigate neuronal interactions controlling movement (stimulate primary motor cortex) following spinal cord injury
- Investigate whether a specific brain area is responsible for a function e.g. speech
What does tDCS do?
Uses low direct current over the scalp to increase or decrease neuronal firing rates
What imaging techniques can be used to assess structure?
DTI - diffusion tensor imaging
What is DTI?
Based on diffusion of water molecules
What is DTI with tractography?
3D reconstruction to assess neural tracts
What is MS - multiple sclerosis?
MS is an autoimmune disorder which results in the loss of myelin from neurons of the CNS
What are some of the main symptoms of MS?
- Blurred vision
- Fatigue
- Difficulty walking
- Paraesthesia (numbness or tingling in different parts of the body)
- Muscle stiffness and spasms
What is orthodromic?
Travelling in the normal direction in a nerve fibre
What is antidromic?
Travelling in the opposite direction to the normal in a nerve fibre
What is M-wave in peripheral nerve stimulation?
The fast response - the activation of the motor axons can cause action potentials to travel along the nerve to cause muscle contraction, a twitch.
How can results peripheral nerve stimulation be recorded?
EMG - electromyography
What is H-reflex in peripheral nerve stimulation?
Reflex activation of a muscle - same stimulus cause activation of the sensory axons (feel stimulus).
- The action potentials can travel along the nerve to the spinal cord.
- These can then cause the lower motor neurons in the spinal cord to become activated.
- Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch.
When can an F wave be seen?
With a large enough stimulus
What is F-wave in peripheral nerve stimulation?
A large electrical stimulus can cause activation of the motor axons to conduct antidromically.
- These action potentials travel along the motor nerve to the spinal cord (i.e. in the opposite way to normal).
- These can then cause the lower motor neurons in the spinal cord to become activated.
- Action potentials in the motor axons can travel along the motor neuron to the muscle where they cause muscle contraction, a twitch.
How does cortical motor stimulation using TMS work?
The activation of the upper motor neurons causes action potentials to travel along the entire motor pathway (upper and lower motor neurons) to cause muscle contraction.
How does cortical motor stimulation using TMS result in?
EMG response known as an MEP - motor evoked potential.
What is the TMCT?
Total Motor Conduction Time:
Time from brain to muscle (MEP latency)
What is the PMCT?
Peripheral motor conduction time:
time from spinal cord to muscle along motor axon
How is PMCT calculated?
PMCT = (M latency + F latency-1) /2
What is the -1 in PMCT calculation?
The -1 is the estimated time for the action potentials arriving at the lower motor neuron cell body to turn around
What is CMCT?
Central Motor Conduction Time
How is CMCT calculated?
TMCT - PMCT
What is the effect of MS on brain stimulation?
Longer than usual MEP latency.
Problem along upper motor neurons, lower motor neurons or both.
What is the effect of MS on TMCT?
Delayed
What is the effect of MS on peripheral nerve stimulation?
Normal F wave latency.
No issue with lower motor neurons.
What is the effect of MS on brain stimulation?
Normal
How can we deduce where the problem is in MS?
TMCT (brain stimulation) delayed
PMCM (peripheral nerve stimulation) normal
-> problem in CNS
