Voluntary Movements II

Why is M1 alone insufficient to explain voluntary movement?

Voluntary movement requires: Intention, Planning, Selection, Coordination, Execution, Feedback correction and therefore involves extensive interactions among motor, sensory and association cortices.

What cortical areas are especially important beyond M1?

Premotor cortex (PMA), Supplementary motor area (SMA), Posterior parietal cortex (PPC), Association cortices, Frontal planning systems, Motor Control Hierarchy.

What are the three hierarchical levels of motor control?

Strategy, Tactics, Execution.

What is the role of the Strategy level?

Determines: Goal of movement, Overall behavioural objective.

Which structures are involved in Strategy?

Association neocortex, Basal ganglia.

What roles do the basal ganglia play in motor strategy?

Filter possible motor programs, Select appropriate strategies, Suppress competing motor programs.

Give an example of Strategy-level processing.

Deciding to pick up a glass.

What is the role of the Tactics level?

Motor programming, Sequencing contractions, Timing movements, Spatial organisation of movement.

Which structures contribute to Tactics?

Motor cortex, Premotor cortex, SMA, Cerebellum.

Give an example of Tactics.

Determining which muscles activate and in what order.

What is the role of the Execution level?

Produces actual movement, Postural adjustments, Reflex coordination.

Which structures contribute to Execution?

Brainstem, Spinal cord, Interneurons, Lower motor neurons, M1.

What is the primary function of M1?

Execution of skilled voluntary movement.

Which body parts are especially dependent on M1?

Fingers, Hands, Face.

How does M1 encode force?

Neuron firing correlates with: Magnitude of force, Direction of force.

What determines muscle force production?

Firing rate of upper motor neurons.

What is population coding?

Movement direction and trajectory are encoded by the combined activity of many neurons.

Why is population coding important?

Single neurons are broadly tuned and cannot independently specify movement direction.

What evidence suggests M1 encodes movements rather than muscles?

One neuron activates multiple muscles, Same movement evoked from different sites, Same muscle represented in multiple locations.

Where is PMA located?

Lateral frontal lobe, Anterior to M1.

Which Brodmann area contains PMA?

Area 6.

What is the primary function of PMA?

Movement selection, Movement preparation, Externally guided movement.

What information does PMA use to select movements?

Sensory information, Previous experience, Current goals.

What is meant by externally guided movement?

Movements triggered by: Visual cues, Auditory cues, Somatosensory cues.

Give examples of externally guided movements.

Seeing a cup and reaching toward it.

What are the two major PMA output pathways?

Indirect: PMA → M1 → spinal cord, Direct: PMA → spinal cord.

Approximately what proportion of corticospinal axons arise from premotor areas?

More than 30%.

Which brainstem system receives PMA projections?

Reticulospinal system.

Functions of PMA-reticulospinal pathways?

Control: Axial muscles, Proximal muscles, Posture, Walking, Limb positioning.

What is feedforward postural control?

Anticipatory postural adjustment occurring before movement begins.

Which cortical area is particularly important for feedforward control?

Premotor cortex.

Example of feedforward postural control?

Before pulling a handle: Gastrocnemius activates, Posture stabilises, Biceps activates.

Is early gastrocnemius activation before an arm pull feedforward or feedback?

Feedforward control.

What is feedback postural control?

Reactive correction after instability occurs.

Which pathways are especially important for feedback postural control?

Vestibulospinal pathways.

What was the key finding of classic delay-period monkey experiments?

PMA neurons fired before movement began.

What occurred during the delay period?

Increased PMA activity despite no movement.

What does PMA activity during delay periods represent?

Movement intention, Preparation, Action selection.

When does M1 activity become strongest?

During actual movement execution.

Where is SMA located?

Medial frontal lobe near the longitudinal fissure.

Which Brodmann area contains SMA?

Area 6.

What is the primary function of SMA?

Internally generated movement.

What are internally generated movements?

Movements initiated from memory or internal goals rather than external stimuli.

Examples of internally generated movements?

Playing piano from memory, Typing a memorised password, Dance choreography.

What role does SMA play in movement sequences?

Important for complex sequential motor programs.

What role does SMA play in bilateral coordination?

Coordinates bimanual tasks.

Examples of SMA-dependent bilateral tasks?

Piano playing, Tying shoelaces, Opening a jar.

Can SMA become active without movement?

Yes. During mental rehearsal of movement.

Why is SMA activation during mental rehearsal important?

Shows motor planning circuits can operate without execution.

Compare PMA and SMA.

PMA: Externally guided, Sensory cue driven, Reaching & grasping, Feedforward posture. SMA: Internally guided, Memory driven, Sequential actions, Bilateral coordination.

Which area specialises in extrapersonal space?

Premotor cortex.

What is extrapersonal space?

Space outside the body used for reaching and grasping objects.

Which area specialises in bimanual coordination?

SMA.

What deficit results from an M1 hand-area lesion?

Loss of precise finger coordination.

Why does an M1 lesion impair finger control?

M1 is essential for skilled, fractionated finger movements.

What deficit results from a premotor cortex lesion?

Difficulty initiating intended movements.

Why does a PMA lesion impair movement initiation?

Movement selection and preparation become impaired.

Major functions of PPC?

Spatial awareness, Attention, Sensorimotor integration, Movement planning.

What information does PPC integrate?

Visual information, Somatosensory information, Motor information.

What does PPC encode during movement?

Movement goals, Target location, Movement trajectories.

Why is PPC important for reaching?

Transforms visual targets into motor commands.

What does PPC determine when reaching for a cup?

Location, Hand orientation, Reach trajectory.

What is the PPC–PMA–M1 sequence?

PPC = where ↓ PMA = how ↓ M1 = execute.

What does motor imagery demonstrate about PPC?

PPC neurons encode specific movement intentions even without movement.

What are mirror neurons?

Neurons activated both when: Performing an action, Observing the same action.

Where are mirror neurons found?

Premotor regions.

Proposed functions of mirror neurons?

Action understanding, Social cognition, Imitation learning, Skill acquisition.

What is the central principle of a BCI?

Decoding intention rather than actual movement.

Outline the major BCI steps.

Record neural activity, Train subject, Build decoder, Predict intended movement, Control device.

What devices can BCIs control?

Cursor, Robotic limb, Wheelchair, Communication device.

What demonstrated modern BCI capability in macaques?

A joystick-controlled cursor was later controlled directly from cortical activity after the joystick was disconnected.

What is a BSI?

A system that decodes cortical intentions and stimulates spinal circuits.

How many cortical electrodes were implanted in the tutorial example?

64 electrodes.

Which cortical regions were recorded?

M1, S1, Premotor cortex, Parietal cortex.

What features are extracted by the decoding algorithm?

Spatial features, Temporal features, Spectral features.

How many epidural spinal electrodes were implanted?

16.

Where were spinal electrodes placed?

Lumbosacral spinal cord.

Which muscles were targeted?

Hip muscles, Knee muscles, Ankle muscles.

What occurred when BSI stimulation was active?

Standing and walking were restored.

What happened when the BSI was switched off?

Walking immediately ceased.

Approximately what is the human cortical surface area?

~2000 cm².

What is the corpus callosum?

The major commissural pathway connecting the hemispheres.

Approximately how many axons are in the corpus callosum?

More than 200 million.

Functions of the corpus callosum?

Interhemispheric communication, Bilateral coordination.

What is association cortex?

Cortex located between primary sensory and primary motor areas that integrates information.

What inputs does association cortex receive?

Sensory cortex, Motor cortex, Thalamus.

Major functions of association cortex?

Integration, Interpretation, Cognition.

Functions of parietal association cortex?

Spatial awareness, Attention, Sensory guidance of movement.

Functions of temporal association cortex?

Object recognition, Storage of factual knowledge.

Functions of frontal association cortex?

Planning, Working memory, Judgement, Decision making.

What is unimodal association cortex?

Processes a single sensory modality.

Example of a unimodal processing pathway?

S1 → anterior parietal cortex → PPC → premotor cortex.

What is multimodal association cortex?

Integrates information from multiple sensory systems.

Examples of multimodal association cortices?

Parahippocampal cortex, Temporal association cortex, Cingulate cortex.

What is an internal model?

A neural mechanism that predicts movement consequences before they occur.

What is reafference?

Sensory feedback generated by one's own movement.

What are examples of interoceptive reafference?

Proprioception, Internal sensorimotor signals.

What are examples of exteroceptive reafference?

Vision, Audition.

What is corollary discharge?

An internal copy of a motor command.

What is another name for corollary discharge?

Efference copy.