week 6: cortical sensorimotor systems

week 6: cortical sensorimotor systems

1. voluntary control of saccades. artificial inteliigience --> sleep improved performance --- growth and pruning

2. cerebral cortex/ 4 lobes. FRONTAL, TEMPORAL, PARIETAL, OCCIPITAL

   • parietal = between basic sensory circuits of temporal + occipital
   • folding in the brain increases surface area.

3. MOVEMENT = M1/ Primary motor cortex. Pre-motor sits in front of M!, supplementary motor = medial edge. FEF = Frontal eye fields. Broca's = langauge production

   • when you have a functioning motor cortex - you can manipulate objects dexterously. Use of fine grain control of force production. loss of these skills after a motor stroke, common signs and symptoms = numbness (somatosensory cortex) + weakness (primary motor cortex)

4. human brains = more folding than other animals. multiple layers of cortex - more processing. other brains - dominated by primary/sensory areas. humans have more higher level/abstract levels of processing> primary areas

5. organisation of the cerebral cortex = cortex forms the outer surface of the forebrain (grey matter). 6 distinct layers/laminae. cortex covers the other subcortical forebrain structures

   • receive info from outside the cortex and send info out. different parts of the brain have slightly different structures/proportions. Cytoarchitectural differences define different areas. BRODMANN DESCRIBES 52
     • M1 (brodmann area 4) contains Betz cells in layer 5 (one of the 2 output layers)
       • large cells, project straight down to brainstem/spinal cord. 1 synpase away from producing a muscular response, fast and fine grained response
     • anatomical distinction in Brodmann areas is functionally relevant

6. observing these connections in humans = TMS. briefly activates areas of the brain. shallow areas. drive responses as cells are activated. activate cortex--> direct to spinal cord

   • Fritsch and Hitzig 1870: electrical stimulation in dog. Mapping of the somatotopic motor representation. Penfield 1940: stimulated during surgery on epileptic patients. Discovered electrical stimulation causes simple movements.

7. mutliple maps: reflect sensory-motor specialisation. cortical motor maps - close mirror rels between sensory and motor maps

   • an organisational pattern, but not clear cut. There is overlap e.g. shoulder-hand-fingers. some muscles will move with eachother based on your regular actions

8. What is being represneted in the motor cortex, muscles or movements? brief stimulation >>> simple movements and contractions of muscles

   • prolonged stimulation >>> complex goal directed actions
     • reaching to grasp, climbing/leaping, hand low down in front, manipulate in front, hand to mouth, chewing or licking, defense
       • for force: power grip = maintain a level of force - virtually no M1 activity. Precision grip = light + hard = graded force production and individual use of fingers = M1 activity

9. Role of M! in motor adaptation: retaining and learning new skills - RETENTION. Cerebellum = acquiring a new skill. codes for muscle forces and dynamic change in forces during voluntary movement

   • outputs connect functionally to related groups of muscles. 5% of output directly connects to spinal motor neurons, large % of output to brainstem + red nuclues
     • mostly makes indirect connections to motor neurons via brainstem and spinal interneurons
       • fine control and fractionation muscle activity, motor cortical stroke = permanent loss of dexterity. important for retention of new motor actions

10. secondary motor/ association areas --> involved in planning.

    • SMA - supplementary motor area --------- PMC - pre motor ---- Dorsal PMd and Ventral PMv ----- PPC- Posterior Parietal cortex
      • secondary areas = very dense connections between them. Heavily connected to the primary, leading to execution of actions. SMA + PMC more involved in planning movements. Brain imaging shows activation when imagining or planning movements- even if action not performed

11. PPC, POSTERIOR PARIETAL CORTEX. Important for maintaining the spatial arrangement of the body in the external environment. Continually integrates sensory + motor input: proprioception, vision and audition, spatial coding

    • SMA, SUPPLEMNTARY MOTOR AREA. considered to be 2 areas to SMA. Proper = Learning, preSMA (execution). postural stability. Planning and executing complex sequential movements. learning new sequences, separation and control of bimanual actions, Initiation of internally generated movements (rather than stimulus driven)
      • PMd Dorsal Premotor - subdivided into rostral and caudal zones, important for preparation of movement, learning conditioned actions (response to external cues). e..g red light, foot on brake
      • PMv Ventral Premotor - important for sensory guidance of movement: responsive to tactile, visual and auditory stimuli. visuomotor control during grasping, mirror neurons. rels with language and brocas area
        • PMv and mirror neurons - first reported in PMv, motor neurons show similar activity when monkey makes a goal directed action and when the same action is being observed visually or heard. Shown in humans with food e.g. strong response when observing and eating food = classical conditioning,
          • Multiple motor cortical areas, each with specialised functions. M1 is the main cortical output area, codes for skilful generation of forces in distal muscles. Premotor and SMA are involved in complex movement, planning and conditioned actions. PPC is complex/ feeds high level mulitmodal sensory information into M1, PMC and SMA

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