Movement Planning

Question 1

what is localisation

Answer 1

representation of the location of the object

Question 2

what is planning

Answer 2

plan of reaching based on the representation

Question 3

what is extrinsic information

Answer 3

• spatial location of the target
  
  • visual information
  • auditory information

Question 4

what is intrinsic information

Answer 4

• kinematic and kinetic information of the body
  
  • muscle spindle - length and velocity of each muscle
  • golgi tendon organs - force produced by each muscle
  • mechanic receptors - force exerted / received on skin

Question 5

how are voluntary movements planned

Answer 5

• spinal reflexes are mostly involuntary: sensory inputs cause motor output directly without the intervention of higher brain centres
• however, voluntary movements require higher-level cortical control
• higher level control centre generates plan, and this plan is transformed to a tool-specific plan (and eventually to individual muscle contractions)

Question 6

what are sensorimotor transformations

Answer 6

• motor control is hierarchical
  
  • in order to go from a general plan defined in extrinsic space (grab an apple) to motor commands in muscle space (contract specific muscles), multi-stage sensorimotor transformations are required
    
    • locate hand and cup (egocentric coordinates)
    • plan hand movement (endpoint trajectory)
    • determine intrinsic plan (joint trajectory)
    • execute movement (joint torques)

Question 7

which different coordinate systems may be employed at different stages of sensorimotor transformations

Answer 7

• extrinsic coordinate systems
  
  • allocentric / egocentric coordinates
  • exteroceptive (sensory) information - visual and auditory
• intrinsic coordinate systems
  
  • joint angle coordinate, muscle lengths (in muscle space)
  • proprioceptive information

Question 8

what is localisation and planning

Answer 8

• after localisation, object is internally represented based in a specific coordinate system
  
  • hand-centered coordinate
  • eye-centered coordinate

Question 9

what is the posterior parietal cortex

Answer 9

• firing of neurons in PPC are related to the movement planning
• lateral intraparietal area (LIP): for saccadic eye movements
• parietal reach region (PRR): for reaching
• anterior intraparietal area (AIP): for grasping
• anatomical proximity of these regions indicates that PPC plans the movement by closely coordinating the eye and the hand

Question 10

how are trajectories planned

Answer 10

• straight trajectory in the hand space: high variability and curved in joint space
• straight trajectory in the joint space: high variability and curved in hand space

Question 11

what is the movement analysis in relation to shape and variability

Answer 11

• Morasso’s study suggests that analysing shape and variability of the movement provide clues about the spaces and coordinate systems the brain uses to localise and plan the movement
• velocity profiles of movements to different distances become identical when duration and peak speeds are scaled
• typical elliptical variability shape of the reaching
  
  • the errors in distance and direction are independent to each other

Question 12

what is variability

Answer 12

• movement inaccuracies arise from errors and variability in the transformations
• source of variability
  
  • input variability: estimation of location and target -sensory noises
  • intrinsic variability: sensors and motor neurons: fluctuations in membrane potentials (neural noise): this limits accuracy and precision of the control
  • output variability: caused by motor neurons and muscles (increased excitability and more motor neurons) - this is called signal dependent noise

Question 13

what are some mathematical solutions related to movement

Answer 13

• with mathematical models, we can predict what movement / force will be generated by the given torques on the joint (or muscle forces), or the other way round
• models that solve forward kinematics / dynamics are called forward models
• models that solve inverse kinematics / dynamics are called inverse models

Question 14

what are internal models

Answer 14

• but obviously we do not solve those mathematicsla formula in our brain, instead we have models with same functions implemented in neural networks. these are called internal models
• the brain has its own internal representation of “how the world (including the own body) works”

Question 15

what is an inverse model

Answer 15

determines the motor commands that will produce a behavioural goal

Question 16

what is a forward model

Answer 16

• stimulated the interaction of the motor system and the world and can therefore predict behaviours
• the forward model uses a copy of motor commands sent to the muscles - efference copy