Motor Cortex

Question 1

Primary motor cortex

Answer 1

• also known as primary motor area, M1 or Bradmann’s area 4
  
  • origin of the corticospinal tract (30% of fibres)

Question 2

somatotopy

Answer 2

• somatotopy is the point-for-point correspondence of an area of the body to a specific region of the central nervous system
• this is shown by the homunculus of the primary motor cortex on the right

Question 3

evidence for somatotopy: Jacksonian March

Answer 3

• observed the pattern for focal epileptic (recurrent) seizures that spread to different parts of the body in a fixed temporal pattern varying from patient to patient
• jackson speculated that the progression or march was due to propagation of activity along the central sulcus
  
  • starts in hand, spreads to arm and neck

Question 4

evidence for somatotopy: mapping the cortex

Answer 4

• Sir David Ferrier (1843-1928, colleague of Hughlings Jackson)
  
  • developments in anesthesia allowed for stimulation of animal brains during surgery
  • electrical stimulation of sections of cortex evoked movements of contralateral body parts
  • identified 15 distinct sections of the cortex that precisely control movements
  • removal of the cortical sections resulted in no movement

Question 5

evidence for somatotopy: the ‘montreal procedure’

Answer 5

• Penfield was a neurosurgen conducting much of his work from McGill University
  
  • treated patients with severe epilepsy by destroying nerve cells in the brain where the seizures originated
  • before operating, Penfield stimulated the brain with electrical probes while the patient was conscious and observed the responses, enabling more accurate surgery
  • also allowed Penfield to map the sensory and motor cortices (human culus)

Question 6

recording from the motor cortex: implantable electrodes

Answer 6

• microelectrodes can be implanted to record local field potential (LFP)
• this is highly invasive but yields high resolution data with low noise

Question 7

recording from the motor cortex: in vivo measures

Answer 7

• electrical activity of cells within the brain can be recorded using direct and indirect measurement techniques
• electroencephalography (EEG) uses electrodes placed on the skull to record brain activity under the recording site
  
  • this is am indirect measure
• electrocorticography (ECoG) uses electrodes placed on the brain tissue to record brain activity
  
  • this is a direct measure

Question 8

extracting movement information from the cortex

Answer 8

• microelectrode array inserted into macaque motor cortex
• single-unit recordings made during reaching movements in multiple directions
• each cell has a “preferred direction” or “directional tuning”

Question 9

Brain-Computer-Interface (BCI) in humans

Answer 9

• during imagined movement, cells display activity specific to that movement
• cells exhibit “directional tuning” similar to the Georgopoulos experiment in monkeys
• study demonstrated the ability to control external devices just by thinking about the movement of their own hand

Question 10

motor cortex also represents force output

Answer 10

• the previous studies demonstrate that the motor cortex represents movement direction but there is evidence that the motor cortex also represents force
• kinematics = movement direction
• kinetics = movement force
• neuronal activity increases or decreases with changes in load
  
  • thus this motor neuron is representing force (i.e. kinetics)
• elite athletes can have functional reorganisation of projections from motor cortex

Question 11

mapping the cortex with transcranial magnetic stimulation

Answer 11

motor cortex can be mapped to find the motor ‘hot spot’

Question 12

motor imagery

Answer 12

expert players demonstrate enhanced cortical excitability in a finger muscle only when observing accurate shots at the point of release