Advanced movements

Sensorimotor transformation

The nervous system converts signal from outside world to one that is understood by the body converting signal into movement 

Optic ataxia

An inability to reach accurately under visual guidance – i.e. making visuomotor sensory transformations

Visuomotor sensory transformations

transforming visual information about the location of objects in extra personal space into the direction of a reaching movement

Supplementary motor cortex

• essential for generating linked self-generated movements.

• Without it we would no longer be able to perform well learned movements and rely on external cues to get things done.

Ballistic movements

• include writing, typing, talking, running etc.

• occur so rapidly that it is almost impossible to depend for their control on the sensory feed-back

Re entrant circuits

Continuous updates about the world that feed back into the brain 

Cerebella Ataxia

• Errors in range and direction of movement.

• Uncontrolled eye movements.

• Unsteady gait.

• Slurred speech and more.

Hypometria and response delays

• Delayed response.

• Issues in engaging an intended action

• Hypometria: movements short of intended goal.

Dysdiadochokinesia

Impaired ability to perform rapid alternating movements.

Hypokinesia

• Insufficient direct pathway output.

• Excess indirect pathway output.

Hyperkinesia

• Excess direct pathway output.

• Insufficient indirect pathway output.

Direct pathway

Stimulates movements

Indirect pathway

Inhibits movement

Muscle rigidity

resistance to passive movement: jerky movement

Akinesia

general paucity (small) of involuntary movement.

Bradykinesia

slowness

Micrographia

Small writing

Parkinsons

• Death of dopaminergic neurons in substantia nigra pars compacta.

• 
  Resting tremor, difficulty initiating voluntary movement (akinesia/bradykinesia), slow shuffling gait.

Huntington’s disease

• Progressive disease with both motor and cognitive symptoms.

• Hereditary atrophy (degeneration) of the caudate nucleus

Basal ganglia

Helps with timing and movement selection

PFC

helps with planning and high level control

Cerebellum

Helps with timing, co ordination and correcting errors

Lateral Intraparietal Area (LIP)

Activity ramps up in anticipation of saccade initiation, peaking at movement onset. The brain can predict when an event is likely to happen and prepare the movement in advance

Principle Nuclei

• Striatum (Caudate + Putamen) and Globus Pallidus.

• Receives information from the cortex

Modulatory / Secondary Nuclei

• Substantia Nigra pars compacta (SNc) and Subthalamic Nucleus (STN).

• helps regulate movement

Circuit pathway

Cortex → Striatum (Inhibition) → Globus Pallidus (Disinhibition) → Thalamus (Excitation) → Motor Cortex.

Saccadic gating

Caudate → Substantia Nigra pars reticulata (SNr) → Superior Colliculus.

Hemiballismus

Unilateral subthalamic nucleus damage causing contralateral involuntary limb movements.

Reinforcement learning

Use reward related signals to help us learn which actions are successful

Motor learning

The putamen helps us learn and adapt movements

Addictive behaviour

• Result of environmental cue-reward associations hijacking basal ganglia reinforcement pathways.

• reward pathways can be influenced by learned associations between environmental cues and rewards

Spinocerebellum

• Input from the spinal cord (proprioception, body position). Arranged topographically, like a body map.

• Processing proprioceptive information from the body.

Cerebrocerebellum

• The largest division of the cerebellum

• Receives inputs from cortex via pons; projects back via dentate nucleus and thalamus.

• Planning co ordinating and fine tuning motor movements

Vestibulocerebellum

Flocculus and nodulus; receives vestibular inputs.(balance)

Internal model hypothesis

• The stereotyped cerebellar microcircuitry acts as a fast feedforward simulator for cognitive operations originating in the prefrontal cortex, correcting predicted vs. actual cognitive outcomes.

• the same error-correcting trick used for movement is reused for thought.

Feedforward simulation

A process where the cerebellum rapidly predicts the sensory or cognitive consequences of an action before sensory feedback returns, allowing fast error correction.