Cerebral Cortex Flashcards
Describe the organisation of grey matter and white matter
Grey matter is on outside and white matter is within the brain.
Grey matter contains cell bodies and white matter and white matter contain neuronal tracts.
What are the three types of fibres and what are their connection?
Association fibres: connect areas within the same hemisphere
Commissural fibres: connect left hemisphere to the right hemisphere (e.g. corpus callosum)
Projection fibres: connect cortex with lower brain structures (e.g. thalamus), brain stem and spinal cord (e.g. corticospinal tract all the way down to alpha motor neurons)
Define the dorsal and ventral surface of the brain?
The dorsal is the outer surface
The ventral is the inner surface
How many layers of grey matter are there?
There are 3 to 6 layers
What is the neocortex?
Part of the cerebral cortex concerned with sight and hearing in mammals most recently evolved part of the cortex
Describe layer 1
Most dorsal, very few neurons, glial cells are present, largely association fibres
Neutropil – an area composed mostly of unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies
Which layer receives input from the thalamus?
Layer 4
Layer 4 is also rich is stellate neruons which are star shape and GABAergic
Summarise the connections of the layers
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem and spinal cord
What type of neurons are found in layer 5?
pyramidal neurons
Betz cells - large motor neurons that project all the way down the spinal cord
How is neocortex arranged?
Lamina (layers) and columns
More dense vertical connections - topical organisation
neurons with similar properties are found in the same column
What are the different lobes of the neocortex?
Frontal
Parietal
Occipital
Temporal
Which corticies are involved in skeletal muscle movement?
Primary motor cortex
Motor association cortex
What are the two parts of the visual association cortex and what are they responsible for?
Dorsal Pathway – responsible for interpretation of spatial relationships and movements WHERE pathway
Ventral Pathway – responsible for form and colour WHAT pathway
What is APRAXIA?
Inability to perform skilled movements with accuracy
What is AGNOSIA?
Disorder of the brain whereby patient can’t interpret sensations correctly despite sense organs and nerves conducting sensation to brain correctly.
auditory agnosia
tactile agnosia
visual agnosia
What is RECEPTIVE APHASIA?
The patient is unable to understand language in its spoken or written form
Compare primary cortices and association cortices?
Primary - function predictable, topographical, left-right symmetry
Association - less predictable function, not organised topographical, left-right symmetry is weak
Discuss use of functional MRI
Decent spatial awareness
Long time to measure response
Blood flow response will take about 5-7 seconds after onset of a stimulus
Lesion of visual association cortex effects?
Lesions of visual posterior association area can result in inability to recognise faces/learn faces
PROSOPAGNOSIA
What is the role of the posterior parietal association cortex?
It creates a SPATIAL MAP of the body in its surroundings from multi-modality information
What could injury of this part of the association cortex lead to?
Disorientation
Inability to read a map or understand spatial relationships
Apraxia
Hemispatial Neglect
What are the consequences of a prefrontal lobotomy?
Change in personality
Inappropriate behaviour
Lack of ability to remember and relate things over time
Attention span and ability to concentrate are diminished
What two areas does the prefrontal cortex receive massive inputs from?
Sensory association cortex (somatosensory, visual and auditory)
Dorsomedial Nucleus of the thalamus
NOTE: lesion of the dorsomedial nucleus will have similar consequences to prefrontal lobotomy
If you give someone with a unilateral parietal lobe lesion something to draw, what will you expect him or her to do?
Hemispatial neglect – they will only draw half of it
What effect do temporal cortex lesions have on memory?
Impaired short-term memory
They are effectively trapped in a 30 second window of memory
Describe hemispheric specialisation.
Right hemisphere = creative + artistic
Left hemisphere = logical + scientific
What is a callosotomy?
A palliative procedure used for the treatment of seizures
The corpus callosum is key for the interhemispheric spread of epileptic activity
Hemispheric specialization test?
A word FACE is flashed to the right and the patient is asked to say what he saw
Left hemisphere is dominant for verbal processing, the patient’s answer matches the word
Word FACE flashed to the left of field of view and patient is asked what he saw
Right hemi cannot share info with left so patient can’t say it but he can draw a face
What is diffusion tensor imaging?
Tractography
Movement of water can infer the integrity of functional pathways, used to estimate pathway of white matter tracts, any occlusion connection is disrupted in the imaging
State two types of brain stimulation testing and what it can be used for.
Transcranial Magnetic Stimulation (TMS)
•Magnetic field induces a current in the cortex causing neurons to fire
•This is method of focally stimulating different areas of the cortex and testing what each area is responsible for
Used therapeutically for severe clinical depression
Transcranial Direct Current Stimulation (TDCS)
•This changes the excitability of neurones but does NOT directly induce neuronal firing
•Anode = increases neuronal excitability
•Cathode = decreases neuronal excitability
•TDCS could be used to reduce motion sickness by suppressing the area of the cortex associated with perceiving vestibular information
Describe and explain how PET (positron emission tomography) scans work. What can it be used for?
A radioactive tracer is attached to a molecule to locate areas of the brain where that molecule is being absorbed
The tracer emits positrons, which are then detected by the receptors
It can be used in Parkinson’s disease to see the uptake of dopamine precursors by dopaminergic neurones
Lower uptake of dopamine in posterolateral putamen in PD patients and can be seen by less light, in Parkinson’s there is a loss in posterolateral putamen wit relative preservation of caudate
What is the difference between MEGs and EEGs ?
MEGs = magnetoencephalography – measures magnetic fields
records magnetic field generated by electrical currents naturally occuring in brain
EEGs = electroencephalography – measures electric fields
non-invasive, electrodes on scalp, voltage fluctuates from ionic current with neurons of brain, less elaborate than MEG
What is a major problem with MEGs and EEGs and how is this resolved?
It is quite noisy – there is a lot of background activity
This is resolved by doing a trial of a large number of participants so that an average can be found
Once the average has been found, it can be deducted from the captured signal to see the underlying activity
What is a fMRI?
Function MRI
It detects changes in blood flow in the brain
It relies on the fact that blood flow in the brain and neuronal activity are coupled – more active parts of the brain require increased blood flow
Which areas of the brain become more active when participants imagine positive events?
Amygdala (almond shape set of neurons located in brain’s deep medial temporal lobe)
Rostral anterior cingulate cortex
What is function of occipital cortex and consequence of a lesion?
visual association cortex analyses different attributes of visual image in different places
form & colour analyzed along ventral pathway; spatial relationships & movement along dorsal pathway
lesions affect specific aspects of visual perception
What is function of temporal cortex and consequence of a lesion?
language, object recognition, memory, emotion
injury leads to AGNOSIA AND RECEPTIVE APHASIA
what is function of parietal cortex and consequence of a lesion?
posterior parietal association cortex creates spatial map of body in surroundings, from multi-modality information
injury may cause disorientation, inability to read map or understand spatial relationships, apraxia, hemispatial neglect
what is function of frontal cortex and consequence of a lesion?
- executive function
judgement, foresight, personality, appreciation of self in relation to world
injury leads to deficits in planning and inappropriate behaviour