Lecture 10 - Motor Control and Disorders of Action

Question 1

how do we control our movements:

Answer 1

Most actions required:

1. multiple muscles
2. precise timing
3. multiple components of movement

Higher cognitive aspects of motor control incl:

1. planning and timing
2. sequencing
3. imagery (mirror neurons)
4. expertise

Question 2

Key brain areas and their function in motor control

Answer 2

Primary Motor cortex = execution

Premotor cortex = preparation of actions

Prefrontal cortex = higher level of planning

Parietal cortex = sensory-motor links

Question 3

Primary motor cortex (M1):

Answer 3

• mapped out somatotopically
• in the precentral gyrus
• Brodmann’s area 4
• responsible for the execution of movement
• contralateral control

Question 4

Brain lesions:

Answer 4

Hemiplegia - Paralysis of one side
Hemiparesis - weakness of one side

(contralateral)

Question 5

M1 coding of movements:

Answer 5

• cells in M1 have a preferred direction
• population of cells code the direction of movement - this is VECTOR CODING
• when movement is in preferential direction of cell this causes that group of cells to fire more than when other movement of direction occurs.

Question 6

population vector

Answer 6

the sum of the preferred tunings of neurons multiplied by their firing rates

Question 7

M1 connections

Answer 7

• input from the supplementary motor area (SMA), premotor area and primary somatosensory area (for sensory information)
• output to spinal cord to control the muscles.

Question 8

Frontal eye fields (FEFs)

Answer 8

• controls the voluntary movement of the eyes
• Broadmanns area 8
• eye movements are guided by external senses (vision and hearing) BUT bodily movements rely on proprioception (concerning position of limbs - this info from somatosensory cortex

Question 9

two main types of eye movement

Answer 9

1. saccades

2. smooth pursuit

Question 10

saccades:

Answer 10

• these are the fastest eye movements that we commonly make - up to 1000deg/sec
• duration around 20 to 200ms
• perception is suppressed during movement

Question 11

smooth pursuit

Answer 11

• smooth tracking movement
• approx up to 50deg/sec
• you need an object to track to do this

Question 12

Premotor cortex:

Answer 12

• the lateral premotor cortex - important for linking action with visual objects in the environment (EXTERNALLY generated actions) e.g. tapping to a beat
• the medial premotor cortex is termed the SUPPLEMENTARY MOTOR AREA (SMA)
• SMA is associated with well-learned actions - well-learnt sequences (INTERNALLY generated action) e.g. you decide to walk

Question 13

what did Swinnen and Wenderoth 2004 find

Answer 13

• areas more active in more difficult bimanual tasks

- e.g. moving one hand in a circle forward and one backward

Question 14

sequence learning (Tone et al 1988)

Answer 14

• looked at brain areas involved in the process of learning a sequence of 8 key presses
• changes from effortful to automatic
  found the following changes:
  
  • decreased activity in dorsolateral prefrontal cortex
  • SMA activity increased
  • lateral premotor cortex activity decreased
  • primary motor cortex activity decreased

Question 14

input to premotor cortex

Answer 14

• lateral premotor cortex: receives visual signals via the parietal cortex (dorsal route)
• medial premotor cortex (SMA) receives strong proprioceptive signals about current position of the limbs

Question 15

Gerloff et al 1997

Answer 15

• Ps had to do simple, scale, or complex sequence tasks
• whilst applying TMS to free frontal regions
• TMS disrupted complex task when on SMA
• TMS over the primary motor cortex affected both ‘complex’ and ‘scale’
• TMS over lateral prefrontal cortex had no affect s
• SMA, therefore, has a critical role in organising forthcoming movements in complex motor patterns

Question 16

Frith et al 1991

Answer 16

• Ps required to generate finger movements that were either predetermined (i.e. move the finger that is touched) OR freely chose which finger to move.
• motor response in both tasks is the same
• bUT dorsolateral prefrontal cortex (PFC) showed greater activation in free-choice task
• SO PFC is involved when there is attention to action
• for longer-term goals and intentions
• not specific to action

Question 17

PFC lesions - what do they cause (x4)

Answer 17

• perseveration - repeat same action when no longer relevant
  
  • utilisation behaviour - act on an irrelevant object in the environment (pick up someone’s glasses)
  • disinhibition - e.g. antisaccade task - releasing behaviours that shouldn’t be done
  • frontal apraxia - not able to follow steps in routine

Question 18

antisaccades:

Answer 18

• required to look in the opposite direction to targets

- must inhibit tendency to look at target

Question 19

Norman and Shallice (1986)

Answer 19

• proposed a model to explain goal-driven action
• this is the SUPERVISORY ATTENTIONAL SYSTEM (SAS)
• Content scheduling is the mechanism that selects a specific schema to be enacted
• SAS only used for novel and less automatic actions
• activation of schemas depends partly on the environment and partly on biasing influence of current and future goals (derived from SAS component)

Question 20

action errors applied to SAS

Answer 20

perservation : unable to change schemas when no longer appropriate
utilisation: schemas activated by the environment without SAS suppressing them.

Question 21

parietal cortex lesions

Answer 21

parietal cortex damage = apraxia (inability to perform skilled purposeful movement
- this issue stems from premotor areas in the posterior parietal cortex.

Question 22

Ideomotor apraxia

Answer 22

INABILITY TO PRODUCE APPROPRIATE GESTURES GIVEN AN OBJECT, WORD OR COMMAND

• idea and execution disconnected
• can recognise action performed by other
• but fails in pantomiming action
• can perform sequence but NOT components
• e.g. pretending to brush teeth - patient can do this without miming the existence of the toothbrush

Question 23

CEREBELLAR PATIENTS

Answer 23

• leads to action tremor
• also dysmetria (over and undershooting movements)
• deficits also in:
  
  • coordinating across joints
  • motor learning
  • timing

Question 24

role of cerebellar network in action

Answer 24

• active during coordination tasks that require one movement to be synchronised with another
• cerebellar loop coordinates the timing and trajectory of movement using sensory and motor information

Question 25

role of basal ganglia motor circuit

Answer 25

regulates excitability of frontal motor structures(SMA) and biases the likelihood of movement and the nature of the movement.

Question 26

Parkinsons disease:

• how many it effects
• 3 main symtpoms

Answer 26

• 1 in 1000

1. bradykinesia (slow movement)
2. tremor
3. muscle rigidity

Question 27

cause of parkinsons:

Answer 27

death of dopaminergic cells in substantia nigra pars compacts in the BG (the pathways linking the substantial nigra and BG)

Question 28

writing with Parkinsons

Answer 28

• micrographia (writing small in size)

- may reduce while writing (size) due to fatigue

Question 29

Parkinson’s disease deficits

Answer 29

• internal/external: more problems with internally generated movements - BG closely linked to SMA involved in internal motor activity
• problems with complex movements and bimanual tasks
• also cognitive effects - attention shifting etc.