Cerebral Cortex Flashcards
What is grey matter composed of
Cell bodies
What is white matter composed of
Axons
Diffusion tenser imaging is an MR modality which looks for XXXXXXX - It looks at YYYY
alignment of water molecules and coincident activity
functional connectivity of circuits
What imaging modality looks for alignment of water molecules and coincident activity- It looks at functional connectivity of circuits
Diffusion tenser MRI
3 types of fibres in the cerebral white matter?
- ASSOCIATION fibres
- COMMISSURAL fibres
- PROJECTION fibres
what do ASSOCIATION fibres connect
Connect areas within the same hemisphere
what do COMMISSURAL fibres connect
Connect left hemisphere to right hemisphere (corpus callosum is the main commissural pathway)
what do PROJECTION fibres connect
Connect cortex with lower brain structures (e.g. thalamus), brain stem and spinal cord
Describe the cerebral cortex
The main bit of the brain
Which fibres Connect cortex with lower brain structures (e.g. thalamus), brain stem and spinal cord
PROJECTION fibres
Which fibres Connect areas within the same hemisphere
ASSOCIATION fibres
Which fibres Connect left hemisphere to right hemisphere (corpus callosum is the main commissural pathway)
PROJECTION fibres
how many layers in the cerebral cortex
3-6
what is the most evolutionarily recent structure in the cortex
Neocortex
How many layer in the neocortex
6
What is in each layer of the neocortex
- Layer 1 Very few, if any, neuronal cell bodies (has some glial cells)- largely local fibres connecting parts of the cortex
- Layers 2/3 Can see the neuronal cell bodies but very small, presence of interneurons
- Layer 4 Largely an input layer- generally input from the thalamus
- Layers 5/6 Output layers- connections to subcortical structures and the longer projections e.g. from the motor cortex down to the brainstem and spinal cord
Layer 1 of the neocortex consists of ….
Very few, if any, neuronal cell bodies (has some glial cells)- largely local fibres connecting parts of the cortex
Layer 2/3 of the neocortex consists of ….
Can see the neuronal cell bodies but very small, presence of interneurons
Layer 4 of the neocortex consists of ….
Largely an input layer- generally input from the thalamus
Layer 5/6 of the neocortex consists of ….
Output layers- connections to subcortical structures and the longer projections e.g. from the motor cortex down to the brainstem and spinal cord
Which is the main output layer of the neocortex
Layers 5/6
Which is the main input from the thalamus layer of the neocortex
Layer 4
layers 1-3 are mainly…
Cortico-Cortical connections
Why is the structure of the visual cortex different to the other cortices
because it has an extra layer of white matter within the cortical structure
what is the other name of the visual cortex
Striate cortex
2 fundamental ways of organising neurons in the cortex?
Laminer and columnar
what is the basis of TOPOGRAPHICAL organisation
closely related neurons work on the same general area (similar properties = same column
Learn the locations of the primary cortices and the association cortices, such as… (6 and 7)
Do it !
Primary motor cortex- In the pre-central gyrus (frontal lobe)
Primary somatosensory cortex- Post-central gyrus (parietal lobe)
Primary visual cortex- In the occipital lobe
Auditory cortex- Superior temporal gyrus (temporal lobe)
Gustatory cortex (taste)- Inferior frontal lobe
Olfactory cortex- Medial temporal lobe
Broca’s area- Inferior frontal lobe (lateralised to left hemisphere)
Wernicke’s area- Junction between parietal and temporal lobe (lateralised to left hemisphere)
Motor association area (premotor cortex)- Immediately anterior to primary motor cortex
Sensory association area- parietal lobe
Visual association area- Occipital lobe
Auditory association area- Immediately posterior to primary auditory cortex
Prefrontal association area- Frontal lobe
What is the taste cortex called
Gustatory
Primary cortices:
Functionally predictable?
Type of organisation?
Symmetry?
Function predictable
Topographical organisation
Left-right symmetry
Assossiation cortices:
Functionally predictable?
Type of organisation?
Symmetry?
Less predictable
Not organised topographically
Left-right symmetry weak/absent
What is the neocortex
a part of the cerebral cortex concerned with sight and hearing in mammals, regarded as the most recently evolved part of the cortex
Injury to the parietal cortex may cause …
may cause disorientation, inability to read a map or understand spatial relationships, apraxia, hemispatial neglect
Temporal cortex is important in
Language
Object recognition o Memory
o Emotion
Injury to the temporal cortex results in…
agnosia
and receptive aphasia
What is receptive aphasia
the patient is unable to understand language in its spoken or written form
Image processing dorsal stream in the visual association cortex is concerned with….
Where (spatial relationships)
Image processing ventral stream in the visual association cortex is concerned with….
What the image is
colour, form
What is agnosia
disorder of the brain whereby the patient cannot interpret sensations correctly although the sense organs and nerves conducting sensation to the brain are functioning normally
disorder of the brain whereby the patient cannot interpret sensations correctly although the sense organs and nerves conducting sensation to the brain are functioning normally is known as
agnosia
Diffusional tensor imaging:
Shows arrangement of what?
Visualises what?
You can use it to estimate what?
Provides index of the arrangement of white matter in the brain
Can be used to visualise white matter pathways
Computational techniques can be used to estimate connectivity between cortical and subcortical regions, e.g. thalamo-cortical loops
Positron Emission Tomography:
How invasive? Why? What needs to happen before you can do PET scan? What is mapped? Cost? Used to image what exactly? Sometimes used in combination with what?
Invasive, patients are injected with a radioactive tracer
PET then measures radioactivity emitted by the tracer
Different types of receptor can be mapped by attaching the tracer to different molecules, e.g. glucose
Expensive, radionuclides must be produced using a cyclotron
Allows imaging of specific receptor populations
Sometimes combined with a computed tomography (CT) scan
Magnetoencephalography:
How invasive?
What does it measure exactly?
Cost?
Temporal resolution?
non-invasive
measures changes in magnetic fields induced by electric currents in the cortex
also very good temporal resolution
magnetic fields not affected by artefacts in the same way as EEG
very expensive Functional magnetic resonance imaging minimally invasive
measures neuronal activity indirectly
poor temporal resolution – measured in secs
better spatial resolution than EEG / MEG – measured in mms
Evoked potential (EP) or event-related potential (ERP):
How invasive?
Temporal resolution?
Spatial resolution?
non-invasive
refined form of EEG recording – directly measure of neuronal activity very good temporal resolution – measured in msec
poor spatial resolution – measured in cms
computer analysis reveals waveforms which are timelocked to particular events. Eg. response of visual cortex to light, activity related to movement, object recognition, cognition
What Can be used to induces brief bursts of activity in focal areas and Prolonged bursts can be used to suppress cortical function?
Direct cortical stimulation using electrodes during surgery Transcranial magnetic stimulation (TMS)
Transcranial direct / alternating current stimulation (TDCS / TACS)
PROSOPAGNOSIA is…
the inability to recognise familiar faces or learn new faces
Lesions where can result in prosopagnosia
visual posterior association area (fusiform gyrus)
Lesions where can result in lack of planning, behaviour becomes disorganised, attention span and concentration diminish, self-control is hugely impaired
FRONTAL CORTEX LESIONS
Lesions where can result in inability to read maps or understand spatial relationships, apraxia, hemi-spatial neglect (ask a patient to draw and you’ll get half the picture (see image))
PARIETAL CORTEX LESIONS
Lesions where can result in agnosia, receptive aphasia
TEMPORAL CORTEX LESIONS
Lesions where can result in subtle lateralised deficits in function
People born without a corpus callosum connecting the hemisphere
Result of a lesion in the TEMPORAL CORTEX ?
agnosia, receptive aphasia
Result of being born without a corpus callosum connecting the hemisphere?
subtle lateralised deficits in function
Result of PARIETAL CORTEX lesions?
inability to read maps or understand spatial relationships, apraxia, hemi-spatial neglect (ask a patient to draw and you’ll get half the picture (see image))
Result of FRONTAL CORTEX LESIONS?
lack of planning, behaviour becomes disorganised, attention span and concentration diminish, self-control is hugely impaired
Result of a lesion in the visual posterior association area (fusiform gyrus)
prosopagnosia
POSITRON EMISSION TOMOGRAPHY:
Use?
Why is it used for this?
How does it work?
Expensive and need radio-ligands, therefore often used as a research tool (David Nutt uses it)- it uses a radioactive tracer attached to a molecule to locate brain areas where that particular molecule is absorbed e.g. dopamine in Parkinson’s
2 ways of stimulating the brain?
TRANSCRANIAL DIRECT CURRENT STIMULATION
TRANSCRANIAL MAGNETIC STIMULATION (TMS)
MAGNETOENCEPHALOGRAPHY (MEG) and ELECTROENCEPHALOPATHY (EEG):
How does each work?
Usefulness?
How to make these more effective?
MEG measures magnetic fields, EEG measure electric fields- they use event-related (‘evoked’) potentials, but they often give ‘noisy’ signals (not very useful) so participants perform large numbers of trials so that an average can be used
FUNCTIONAL MAGNETIC RESONANCE IMAGING (fMRI):
What does it look at?
How does it work?
The golden standard of imaging modalities- we can get information in vivo about connectivity. Is usually about monitoring blood flow or glucose metabolism- higher activity is seen in areas using more glucose and therefore receiving more blood flow (see below for slide on use of fMRI in measuring positive and negative thoughts)
4 ways of measuring and imaging brain activity?
MAGNETOENCEPHALOGRAPHY (MEG) and ELECTROENCEPHALOPATHY (EEG
FUNCTIONAL MAGNETIC RESONANCE IMAGING (fMRI
POSITRON EMISSION TOMOGRAPHY
