Organisation of cerebral cortex Flashcards
What are the three types of fibre of the cerebral white matter?
Association fibres= connect with areas in same hemisphere
Commisural fibres= connect with two hemispheres
Projection fibres= connect the cortex with lower brain structures (e.g. thalamus), brainstem and spinal cord
How is the grey matter organised?
It is organised into layers (laminar structure) with 3-6 cortical layers which are designated by roman numerals with letters for laminar subdivisions
Where are each of the cortical laminae?
In the neocortex (which covers the bulk of cerebral hemispheres and is defined by 6 layers)- each cortical laminae have characteristic functional and anatomical features
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
What are the different connections of the different layers of cortex?
Layer 1-3 mainly cortico-cortical connections
Layer 4- input from the thalalmus
Layer 5-6- connections with subcortical, brainstem and spinal cord
What does layer 1 mainly contain?
Neuropil- area composed mostly of unmyelinated axons, dendrites and glial cell processes that form a synaptically dense region containing a relatively low number of cell bodies
What is layer 4 typically rich in?
Stellate neurones with locally ramifying axons, in the primary sensory cortices-these neurones receive input from thalamus
What do layer 5 and layer 4 to a lesser extent contain?
Pyrimidal neurones whose axons typically leave the cortex
What are the neurones locally organised into?
Columns with dense vertical connections so they talk to each other and have specific function
What are neuronal columns the basis for?
Topographical organisation
What is the occipital cortex involved with?
Vision:
Visual cortex and Visual association cortex
What does the visual association cortex do?
It analyses different attributes of visual images in different places
Form and colour are analysed along ventral pathway
Spatial relationships and movements are analysed along dorsal pathway
What is the parietal lobe involved with?
Sensory information from skin, musculoskeletal system, viscera and taste buds: Primary somatic sensory cortex and sensory association area
What does the posterior parietal association cortex do?
It creates a spatial map of body in its surroundings from multi-modality information
What does injury to the posterior parietal association cortex lead to?
It may cause disorientation, inability to read a map or understand spatial relationships, apraxia, hemispatial neglect
What is apraxia?
Inability to make skilled movements with accuracy
What is the temporal lobe involved with?
Language
Object recognition
Memory
Emotion
What does injury to the temporal lobe lead to?
Agnosia- auditory, visual and tactile
Receptive aphasia
What is agnosia?
Disorder of brain whereby patient can’t interpret sensations correctly although the sense organs and nerves conducting sensation to brain function normally
Auditory- can hear but can’t interpret
Tactile- Normal sensation in hands but can’t recognise 3D objects with touch alone
Visual- See but can’t interpret symbols
What is receptive aphasia?
Patient is unable to understand language in its spoken or written form
What is the frontal lobe involved in?
Coordinates information from other association areas and controls some behaviours: Judgement Foresight Personality Appreciation of self
What does injury to the frontal lobe lead to?
Deficits in planning and inappropriate behaviour
How do primary cortices and association cortices compare?
Primary cortices:
Function is predictable
Organised topographically
Left-right symmetry
Association cortices:
Less predictable
Not organised topographically
Left-right symmetry is weak or absent
How are image attributes processed?
Seperately:
What (colour and form)- ventral stream
Where (spatial relationships)- Dorsal stream
What is prosopagnosia?
Where lesions of the visual posterior association area can result in ability to recognise faces or learn new faces but other parts are intact
What did frontal cortex lesions show in Phineas Gage?
His personality changed- became unreliable, impulsive with little regard for consequences and became an alcoholic
There is a lco of ability to remember and relate things
Attention span and concentration diminish
Abstract reasoning disappears
From where does the prefrontal cortex receive massive inputs from?
Sensory association cortex and dorsomedial nucleus of thalamus
What do lesions of dorsomedial nucleus of thalamus produce?
Many of the same symptoms as prefrontal lobotomy
In terms of the parietal lobe, what types of stroke are more common than others?
Right parietal lobe strokes are more common than left
How do patients with parietal lobe strokes present?
These patients have no problem with vision but if you give them something to draw, they will draw half of it and then stop halfway. This is a deficit of attention
What does the temporal lobe connect?
Emotions, memory and language
What will lesions of temporal lobe impair?
Short term memory- effectively trapped in 30 second window of memory
What specialisation is there within hemispheres?
Right hemisphere- artistic and creative
Left hemisphere- logical and scientific
What is a callosotomy?
Palliative surgical procedure for treatment of seizures because corpus callosum is key for interhemispheric spread of epileptic activity
How is diffusion tensor imaging- tractography used?
Movement of water molecules in brain can be used to infer underlying structure of white matter. This information is used to estimate location and connections between different white matter pathways
In which patients do white matter connections become disrupted?
Patients with traumatic brain injury or concussion injuries in sports such as boxing
How does transcranial magnetic stimulation (TMS) work?
It is a method of focally stimulating different areas of the cortex. Putting a current through wire coil induces a current through your brain. This means that you can briefly activate a brain area and test which specific brain area is responsible for certain functions
How does transcranial direct current stimulation (TDCS) work?
It changes the local excitability of neurones, increasing or decreasing the firing rate. This doesn’t directly induce neuronal firing. The anode increases excitability and cathode decreases excitability
What can TDCS be used to treat?
It could be used to reduce motion sickness by suppressing the area of cortex associated with processing vestibular information
How does positron emission tomography (PET) work?
It uses a radioactive tracer attached to a molecule to locate brain areas where that particular molecule e.g. dopamine is being absorbed
What are the pros and cons of PET?
It is expensive but has good spatial resolution and specificity in terms of underlying biology (only way to identify brain regions absorbing particular substances
What is the difference between magnetoencephalography (MEG) and electroencephalography (EEG)?
MEG:
Measures magnetic fields
Maps brain activity by recording magnetic fields produced by electrical currents occuring naturally in brain
EEG:
Measures electric fields
Records electrical activity of the brain
Less elaborate than MEG
What similarities are there between MEG and EEG?
Both non-invasive
Both signals are noisy
How does functional magnetic resonance imaging work?
Measures brain activity by detecting changes associated with blood flow. This relies on fact that cerebral blood flow and neuronal activation are coupled- blood flow increases when area of brain in use
How was optimism measured?
When participants imagined positive events in the future or past, the amygdala and rostral anterior cingulate cortex were more active than when they imagined negative events
