Topic 4-Action

• Action: change the environment to make it more suitable for the organism to survive.
• Somatic vs autonomic:

  1. Somatic
  2. skeletal muscles: move limbs
  3. Autonomic
  4. smooth muscles: change blood pressure, digest food
  5. cardiac muscles: heartbeat
  6. endocrine glands: secrete hormones
  7. exocrine glands: secrete sweat
• Inverse model: current position and desired position to motor commands (used to create motor plans)
• Forward models: current position and motor commands to predicted position (used to evaluate motor plans and actions)
• Efference copy: internal copy of a motor command
• Feedforward vs feedback:

  1. Feedforward control
  2. motor command sent to muscle
  3. faster but less accurate
  4. Feedback control
  5. motor command sent to muscle
  6. actual state compared to desired state
• Would a feedforward controller use a forwardmodel or an inverse model?

  Forward
• Premotor cortex:

  • involved in selecting goals and planning actions at a conceptual level
  • particularly when plans are driven by external stimuli
  • planning in premotor cortex occurs before voluntary movement
• Mirror neurons:

  • some neurons in premotor cortex represent actions at a conceptual level
  • performing or observing an action
• Supplementary motor cortex (SMA):

  • involved in selecting goals and planning actions at a conceptual level
  • particularly when plans involve an internally generated sequence of actions
• Motor representation and motor cortex:

  • motor cortex represents directional movements of body parts, not specific muscle actions
  • signals from motor cortex travel direclty to lower motor neurons and lower circuit neurons in brainstem and spinal cord
• Population vector:

  • treat firing of each neuron as a vector
  • direction = preferred direction
  • length = firing rate
  • add up vectors for all neurons
  • population vector: accurately represents actual movement direction
• Basal ganglia:

  • help to select, initiate, and inhibit movements through cortico-basal ganglia-thalamocortical loops
  • critical to dopamine-based reinforcement learning
  • participate in motor control, cognitive control, and emotional control
• Basal ganglia direct pathway:

  1. Cortex
  2. Striatum
  3. Globus pallidus pars interna/substantia nigra
  4. Thalamus
  5. Cortex
• Basal ganglia indirect pathway:

  • Cortex
  • Striatum
  • Globus pallidus pars externa
  • Subthalamic nucleus
  • Globus pallidus pars interna/substantia nigra
  • Thalamus
  • Cortex
• Action initiation: direct pathway

  Action inhibition: indirect pathway

  • acts as a closing gate
• Reinforcement learning:

  • unexpected rewards generate dopamine signals from the substantia nigra
  • this excites the direct pathway and inhibits the indirect pathway
  • this allows modification of behaviour based on reward
• Motor coordination and cerebellum:

  • uses forward model to predict results of motor commands
  • uses differences between actual results and predicted results for:
  • online error correction
  • motor learning
  • feedback control
• Fitt's law: the speed/accuracy tradeoff for pointing motions

  • Time, T, depends on:
  • Distance to target (D)
  • Width of target (W)
  • Initiation time for limb (a)
  • Relative pace of limb (b)
• From cortex to spinal cord:

  • axons from primary motor cortex synapse directly on lower motor neurons and local circuit neurons
  • spinal cord circuits can also control movements on thier own
• Central pattern generators:

  • local circuits in spinal cord:
  • can control complex movements
  • can respond to environmental changes
  • do not require higher-level input
• Motor action and muscles:

  • lower motor neurons synapse directly on muscle fibers
  • release of neurotransmitter causes muscle fiber to contract
  • muscle spindles detect changes in muscle length and send them back to spinal cord via dorsal root ganglion
• Types of electrical recordings:

  1. Intracellular
  2. voltage clamp
  3. patch clamp
  4. Extracellular
  5. single-unit recording
  6. multi-electrode recording
• Ethical concerns with animal experimentation:

  • care and housing
  • surgical implantations of electrodes
  • training and performance
  • killing/sacrific after experiment
• If an animal stepped on a sharp tack with the right hind limb, the left hindlimb would receive:

  • excitatory signals to the motor neurons for the extensor muscle
  • inhibitory signal to the motor neurons for the flexor muscle
• According to Fitt's law:

  • the time to move to a target increases as the distance to the target gets longer
  • the time to move to a target decreases as the width of the target gets larger
• Role of premotor cortex in motor planning:

  • multiple potential motor plans can be generated in preparation for action
• An efference copy of a motor command can be used as input for a forward model in order to predict behaviour for use in feedback control
• In feedforward control, an inverse model is given the desired result and outputs a motor command that is intended to achieve that result
• Lower motor neurons: motor neurons that connect the CNS to the muscles
• Central pattern generator: a collection of neurons within the central nervous system that is able to spontaneously generate and maintain rhythmic movements