Matt Roser L4 Flashcards
What are the hemispheres of the brain separated by?
The longitudinal/sagittal fissure
How are the hemispheres of the brain connected?
by commissures, which are tracts of white matter
What is the biggest commissure?
Corpus callosum > 200 million axons (95% myelinated)
Where are subcortical commissures?
Between subcortical nuclei
Which cortices connect across the hemispheres?
Associative cortices
Homotopic connections
Across hemispheres to same region
Heterotopic connections
Across hemisphere to different region
Ipsilateral connections
To different regions within the same side of the brain
Midline fusion
Strict homotopy between primary cortices across the corpus callosum
Anatomical asymmetries of the brain (3)
Anterior right hem/posterior left hem overlap midline, Sylvian fissure longer in left and ascends more anteriorly in right, underlying regional size/myelinisation
How do we test each hemisphere of the brain? (3)
lateralised visual presentation, dichotic listening, fMRI statistical lateralisation map
Commissurotomy
Surgery separating the corpus callosum
Callosotomy
Surgery separates some or all of the corpus callosum in order to stop atonic seizures (drop attacks).
Disconnection syndrome
A collection of symptoms which appear when the corpus callosum is severed i.e. difficulty paying attention and slower processing of information
How do we assess hemispheric integration in individuals who have had a commissurotomy?
- Subcortical commissures and what info can be transferred
- partial callosotomy showing specificity of transfer
Partial or staged callosotomy - what part of the corpus callosum is responsible for what information transfer?
Anterior - semantic
Central - motor
Posterior - sensory
What has unilateral brain damage shown for language processing?
That in 97% RH and 70% LH, language centres are predominantly left-hemispheric
How is language processing presented in patients with split-brain disconnection syndrome?
language is predominantly left-hemispheric, and only in the right visual field can stimuli be named. The right hemisphere still has a lexical ability (knows what it is seeing) just not grammatical
Normal brain Non-word decision
Stronger in the right visual field and ear -> left hemisphere associated with faster and more accurate responses
Normal brain semantic priming
Semantic priming is the provision of stimuli that are semantically related to the next stimuli. Stronger in RVF
What is the difference between simple and sophisticated visuospatial processes in split-brain patients?
Simple processes (illusory contours) are bilateral, yet more complex processes (amodal completion) draw on the right hemisphere
What are the hemispheres best at processing respectively?
LH is a sophisticated language processor and RH is a sophisticated visuospatial processor
What is the RH superior at processing with respect to higher level percepts?
construction, detecting offset, orientation, mirror reversal, and perceiving degraded stimuli
Hemispheric prediction
The left hemisphere confabulates and looks for patterns
The left-hemisphere interpreter
The function of the left hemisphere attempting to give a causal explanation for events, behaviors or feelings (chicken and shovel)
When is there cooperation between the two hemispheres?
When tasks become more difficult there is a bilateral advantage (better when displayed bilaterally)
When is there competition between the two hemispheres?
- Motor inhibition via corpus callosum between motor cortices (decoupling)
- When developing language abilities in the left hemisphere it inhibits the development in the right hemisphere - but LBD early in development often allows for the LH processes to be born in the RH
Why has the brain evolved to be divided?
The most efficient use of cortical space and allows for faster intrahemispheric processing - necessary for language etc.
Are hemispheric differences fluid or dichotomous?
Relative and fluid, even for domains most commonly characterised as lateralised - language
When can lateralised processes change?
With certain stimuli, task requirements and task difficulty
Aristotle on the mind and body
Soul is the essence of being and the mind is centred on the heart
Galen on the mind and body
Pneumatic theory of brain - brain was a pump filled with animal spirits which affected behaviour
Vesalius on the mind and body
predecessor of Descartes - increased knowledge of human anatomy
Descartes on the mind and body
- Dangerously promoted the possibility of a science of the mind
- Mechanistic view of behaviour - animal study/automata/reflex mechanism
Cartesian Dualism
Mind and body are separate realms
Cogito, ergo sum
I think therefore I am - the existence of the soul is indubitable
Extensions of Descartes’ mechanistic view (3):
- Conditioning (Pavlov’s dog)
- Behaviourism (stimulus responses)
- Cognitive revolution (1960s) mentalistic structures
Modern perspective of mind and body
monist/materialist - psychological phenomena are to be accounted for as effects of organic changes in the brain and nervous system
Modern perspectives of consciousness (6):
- Awakness
- General alertness
- Focal attention
- Reflective (metacognition)
- Self-awareness
- Qualia (subjective)
First 5 = access consciousness - examined by cog.neuroscience
Last = Phenomenal consciousness
Three tractable characteristics of consciousness
Operationalised (defined), implementation (in an artificial neural network) and adaptivity (evolutionary)
Processing of a stimulus may reach consciousness only if it is integrated into a:
large-scale system of cortical activity (a global neuronal workspace)
What is consciousness in the brain?
A global pattern of activity across the brain
Interaction of modular processes allowing information to be maintained and influence other processes is characteristic of:
Attentional amplification in the prefrontal cortex
When do processes become a part of consciousness?
When modular processes integrate with the global workspace network
Fractionated consciousness
Associated with lesion patients having reduced awareness of their functions
Blindsight
residual visual function to navigate an area but no residual consciousness
Anosognosia for hemiplegia and neglect
confabulation to interpret the world in a way consistent with conscious experience
Fractioned Consciousness and the global neuronal workspace
A patient may lack awareness because there is a disruption to the mechanisms linking local processes to global patterns of activation
