15 - Cerebral cortex Flashcards
Describe the distribution of the grey and white matter in the brain?
Grey matter: on the surface of the brain. Nerve cell bodies.
White matter: the circuitry (axons and connections).
What are the three types of fibre that make up white matter?
Association Fibres – connect with areas in the same hemisphere - LOCAL CIRCUITRY
Commissural Fibres – connect the two hemispheres
Projection Fibres – connect the cortex with lower brain structures (e.g. thalamus)
How many layers of grey matter are there?
3-6 (they are usually numbered by roman numerals)
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
Describe the different connections of the 6 layers of grey matter.
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem and spinal cord
What does layer 1 mainly consist of?
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
What type of neurone is found in layer 4?
Stellate neurones
What type of neurone is found in layer 5?
Pyramidal neurones
How is the frontal cortex (frontal cortex includes the premotor cortex, and the primary motor cortex) defined??
defined posteriorly by the central sulcus
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
Ventral Pathway – responsible for form and colour
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 posterior parietal association cortex lead to?
Disorientation
Inability to read a map or understand spatial relationships
Apraxia
Hemispatial Neglect
Define apraxia.
Inability to make skilled movements with accuracy
What is the temporal association cortex responsible for?
Language
Object Recognition
Memory
Emotions
What are the two main consequences of injury to the temporal lobe?
AGNOSIA – inability for the brain to interpret sensory information although the nerves carrying sensory information to the brain are fine
E.g. visual agnosia – patients can see perfectly fine but they can’t interpret sympbols such as letters
RECEPTIVE APHASIA – unable to understand language in the spoken or written forms
What is the role of the frontal lobe?
Executive functions e.g. planning, judgement, foresight, personality
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
What are where are the speech areas?
Broca’s area (inferior frontal lobe)
Wernicke’s area (junction between parietal/temporal)
These areas are specific, but they are lateralised to the left hemisphere
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
State a type of imaging that uses the movement of water molecules in the brain to infer the underlying structure of white matter.
Diffusion Tensor Imaging – Tractography
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
• This is method of focally stimulating different areas of the cortex and testing what each area is responsible for
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 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
What is the difference between MEGs and EEGs?
MEGs = magnetoencephalography – measures magnetic fields EEGs = electroencephalography – measures electric fields
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 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
Rostral anterior cingulate cortex
What is the biggest commissural pathway in the brain?
corpus callosum
What is the biggest projection pathway in the brain?
corticopsinal tract
How many layers of the neocortex is there?
6 layers
NOTE: most of the cortex has 6 layers, but the grey matter can have 3-6 layers
What does layer 1 of the cortex mainly consist of?
Neutropil – an area composed mostly of unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a low number of cell bodies
What functions are localised in the occipital lobe?
contains the primary visual cortex and visual association cortex
The visual association cortex analyses different attributes of visual image in different places.
ventral pathway = form & colour
dorsal pathway = spatial relationships & movement
What functions are localised in the parietal lobe?
Primary somatosensory cortex is located in the post-central gyrus in the parietal lobe
Posterior parietal association cortex creates spatial map of body in surroundings, from multi-modality information.
What functions are localised in the temporal lobe?
Auditory cortex in the superior temporal gyrus in the temporal lobe
Language, object recognition, memory, emotion
What functions are localised in the frontal lobe?
Primary motor cortex is located in the pre-central gyrus in the frontal lobe
Judgement, foresight, personality, appreciation of self in relation to world
Where are the motor association areas located?
anterior to the primary motor cortex in the frontal lobe
Where are the parietal association areas located? What functions are localised here?
Located in the parietal cortex (duh)
This is where integration occurs of multiple sensory modalities
Where are the auditory association areas located?
immediately adjacent to the primary auditory cortex
What are the 2 main visual processing pathways once information reaches the PVC?
- The dorsal stream
WHERE – spatial relationship - The ventral stream
WHAT – colour, form
Describe the effects of lesions of the visual association cortex, in particular the visual posterior association area (fusiform gyrus)
prosopagnosia - inability to recognize familiar faces or learn new faces
Describe the effects of frontal cortex lesions
Characterised by a lack of planning, behaviour becomes disorganised, attention span and concentration diminish and self-control is hugely impaired (disinhibition).
Describe the effects of parietal cortex lesions, in particular the posterior parietal association cortex
- Injury may cause disorientation, inability to read maps or understand spatial relationships, apraxia and hemispatial neglect
- Patients lose their visual-spatial integration
Describe the effects of temporal cortex lesions
How can this be treated?
- Injury leads to agnosia and receptive aphasia (difficulty understanding written and spoken language)
- This can now be effectively treated by removal of the damaged portion of the temporal lobe
- In the olden days, the solution was to do a bilateral temporalobectomy
- This resulted in dense anterograde amnesia
Apraxia vs agnosia
*go more in detail - don’t see how it relates to the lobes of the brain
apraxia - disorder of motor planning
parietal cortex lesion
agnosia - inability to recognise objects
temporal cortex lesion
