Movement planning (wk1) Flashcards
What is the destination (target)?
-> Extrinsic information: spatial location of the target (visual + auditory information)
What is the intrinsic information and where is it in the body?
-> Intrinsic information: kinematic and kinetic information of the body
1. Muscle spindle – length and velocity of each muscle
2. Golgi tendon organs – force produced by each muscle
3. Mechanoreceptors – force exerted/ received on skim
How are voluntary movements hierarchically planned?
-Spinal reflexes and higher-level cortical control
-Spinal reflexes -> Mostly involuntary: Sensory inputs cause motor output directly without the intervention of higher brain centres.
-Voluntary movements require higher-level cortical control. Higher level control centres generates a general plan, and this plan is transformed to a tool-specific plan (and eventually to individual muscle contractions)
Hierarchical motor control
-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
What are coordinate systems?
Different coordinate systems must be employed at different stages of sensorimotor transformations.
Describe the 2 extrinsic coordinate systems:
- Allocentric/ egocentric coordinates
- Exteroceptive (sensory) information – visual and auditory
Describe the 2 intrinsic coordinate systems
-Joint angle and proprioceptive info
- Joint angle coordinate, muscle lengths (in muscle space)
- Proprioceptive information
-Localisation and Planning -> Posterior Parietal Cortex (in the monkey brain). Firing of neurons in PPC are related to the movement planning. LIP for saccadic eye movement (jumpy eye movement). PRR for reaching. AIP for grasping. Anatomical proximity of these regions indicates that PPC plans the movement by closely coordinating the eye and the hand. Three areas are close together due to the hand and eye movement which work together.
Describe the experimental evidence for eye-centred planning of reaching movement (Bastia et al 1999)
-Neural recordings of Parietal Reach Region (reach planning) for different initial gaze directions and hand positions.
-The firing pattern highly correlates with gaze direction, not with hand position.
-Firing pattern of neurons should correlate with eye direction
-Large neuron activity are under the eye but opposite direction to the hand (this means neuron firing activity relate to the eye direction more than the hand position of the monkey) – emphasises importance of vision.
How are trajectories planned (2 choices):
- Straight trajectory in the hand (=end-effector) space (-> curved in joint space -> high variability in joint space)
- Straight trajectory in the joint space (-> curved in hand space -> high variability in hand space)
How are trajectories planned in hand space (Morasso 1981)?
-Trajectories are planned in hand space (Morasso 1981) -> 2D reaching movement from/to different positions on the plane. Recorded temporal profiles of hand position (end-effector space) and joint angle (configuration space) changes.
* Movements tend to occur along straight lines in the hand space
* Well-maintained bell-shaped profiles of the hand speed
* Higher variability was observed in the joint space
(speed profile is also called velocity profile)
Describe shape and variability in motor control studies:
-> Typical elliptical variability shape of the reaching – the errors in distance and direction are independent to each other.
-Movement inaccuracies arise from errors and variability in transformations
Describe the 3 sources 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 + more motor neurons) – this is called signal-dependent noise
How can the brain solve kinematics and dynamic problems of our own body?
-Mathematical solutions -> 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 around. Models that solve forward kinematics/ dynamics are called forward models. Models that solve inverse kinematics/ dynamics are called inverse models
What is the internal model?
-> First conceptualised by Kenneth Craik in 1934. The brain has an internal representation of ‘how the world (including the own body) works’.
What are the forward and inverse model?
-Internal models – Inverse Model -> The inverse model determines the motor commands that will produce a behavioural goal
-Internal models – Forward model -> The forward model simulates 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.
