Systems level architecture

Systems level architecture

1. Evolution

   • Brains a product of
   • Essential concepts
     • All biological systems produce more offspring than can survive
     • Probabilistic nature of conception leads to variability in offspring
     • The world is a harsh place where only those able solve the problems of life survive and reproduce – natural selection
       • Therefore, biological characteristics (including the brain) ‘sculpted’ by evolution to solve life’s problems
         • This process has been going for millions of years so there is a profusion of solutions running around
   • Problems solved by nervous systems
     • Basic problems associated with:
       • Staying alive: avoidance of harm, body maintenance (feeding/drinking/temperature)
       • Reproduction: sex and nurturing
     • In a changing world flexibility is the key to survival
       • The ability to model many aspects of the physical world (external and internal) accurately
         • Sensory/motivational processes
       • The ability to move and interact with the physical world
         • Motor systems
       • An appreciation of context and ability to integrate information from different sources
         • Cognition
   • Phylogenetic scale
     • We see increasingly sophisticated solutions
       • Fundamental architecture remains the same
         • This is reflected in systematic changes in brain structures – e.g. some have got bigger/more elaborate
         • But the basic architectural organisation has been retained within the brains of all vertebrates
           • Indicates why studies of lower species e.g. rats can inform us about how the human brain operates
       • Evolution develops increasingly sophisticated functional systems
         • Brain comprises hierarchy of functional systems providing increasingly sophisticated competences

2. Fundamental processing units

   • If we want to know what the vertebrate brain does…important to identify the fundamental architectural components and determine their functions
   • Localisation of function
     • Different areas of the brain perform different tasks
       • 1. Cortical and brainstem structures with specific function:
         • Visual cortex/midbrain superior colliculus primary sensory areas processing information from eye
         • Hand area in motor cortex/trigeminal motor nucleus primary motor structures providing commands for fine movements of fingers and mouth
       • 2. Neural systems with a generic function
         • A structure with repeating micro-architecture that processes information received from regions performing widely differing functions
         • leads to idea of general/generic functions required for most/all tasks…e.g. attention, honing skills, memories of events, reward
   • Basic processing unit 1: Regions that generate behavioural options
     • Sensorimotor structures
       • cerebral cortex
       • Midbrain
       • Hindbrain
       • Each of these general brain divisions have sensory areas that project to motor areas that produce movement
       • Example
         • The midbrain superior colliculus
           • Input from the retina
             • Output to the eye muscles
               • Evoked eye movements
                 • Bring novel events onto the fovea
           • Retinotopic map of the visual world

3. The cerebellum

   • Re-entrant loop architecture
     • All sensorimotor, cognitive and motivational/affective structures connect to the cerebellum via re-entrant loops
       • Structure of origin
         • Pons
           • Cerebellum
             • (Thalamus)
               • Structure of origin
   • Architecture
     • Structure of cerebellar cortex has uniform microarchitecture over its entire surface
     • Different cerebellar regions have different inputs and outputs, but same basic organization
       • Therefore repeating microarchitecture is performing the same operation on different inputs
   • Generic function
     • Damage makes many movements inaccurate, slow and uncoordinated
     • Other parts of the brain issue movement commands - cerebellum ensures they are carried out properly
     • Predicts sensory consequences of own actions….so they can be ignored…..or improved if there is an error….skill development

4. The Hippocampus

   • Located in the temporal lobe
   • Part of the limbic system
   • External inputs
     • Different (sensorimotor, cognitive motivational/affective) functional systems contact different territories
     • Territories spatially distributed
     • Microarchitecture common to all terrritories
   • Generic function
     • Critical for episodic memory
     • Essential for construction of mental images
     • Vital role in short term memory
     • Spatial memory and navigation

5. Basal ganglia

   • Function
     • Selection
     • Reinforcement

6. See lecture for summary slides

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