Motor Control

• Cerebellum

• Basal Ganglia

• Motor Cortices

Cerebellum

• General principles

– formation of loops

– modulatory

– ipsilateral

– midline versus lateral

Cerebellum

• Contains two hemispheres

• three divisions

– vermis

– intermediate zone

– lateral zone

Cerebellum

• Vermis - fastigial nucleus

• intermediate zone - interpositus nucleus

• lateral zone - dentate nucleus

Vermis

• Receives somatosensory information and kinesthetic information

• Postural adjustments

• Lesion: fall toward ipsilateral side.

Intermediate Zone

• Receives info from red nucleus and somatosensory info from spinal cord

• Lesion: ridigity, difficulty in moving limbs.

• Lesion: action (intention tremor)

Lateral zone

• Input from motor and association cortices through pons.

• Lesion: ballistic movement.

• Lesion: coordination of multijoint movements (decomposition of movement)

Lateral Zone

• Learning new movements

• Cognitive functions (simple, but precise time tapping movements)

• Cognitive - judgments about time (central timing mechanism).

Basal Ganglia

• Caudate nucleus and putamen are known collectively as the striatum

• receive all input

Basal Ganglia

• Globus pallidus (pallidum)

• main output pathway that connects with thalamus

• motor/nonmotor regions: dorsolateral, orbitofrontal

Basal Ganglia

• Movements that take time to initiate or stop.

– Setting the motor system with regard to posture

– preparing nervous system

– motor planning and learning

Basal Ganglia

• Substantia nigra

• subthalamic nucleus

Basal Ganglia

• Striatum connects to globus pallidus by two routes.

– Direct

• sustaining/facilitating ongoing action

– Indirect

• surpresses unwanted movement

Lesions to Basal Ganglia

• Akinesia

• bradykinesia

• tremors

– rhythmic, oscillating.

• Parkinsons

– damage to substantia nigra

• no input to direct pathway

• indirect pathway becomes overactive

Lesions to Basal Ganglia

• Striatum damaged

– indirect pathway from striatum to globus pallidus is underactive

• hyperkinesis

• chorea

• athetosis

• This is what happens in Huntington’s disease!

Motor Cortices

• Motor program

– abstract representation of an intended movement

– outside motor cortex

• supplementary motor

• anterior cingulate

• frontal eye fields

• parietal regions

Supplementary Motor Area (SMA)

• Often called premotor

• Projections

– ipsilateral, contralateral, and contralateral SMA

• Lesion

– difficulty in bimanual coordination

• Imaging

– active when asked to imagine movement

Anterior Cingulate

• Cognitive control of movement

• Novel and unrehearsed movements

• PET study

– manual movements

• caudal

– oculomotor

• rostral

– speech

• in between

Frontal Eye Fields

• Voluntary eye movements

• Synapse on brain-stem

– 3rd, 4th, 6th cranial nerves

• Frontal eyefields have precedence over superior colliculi

• Lesion: can’t inhibit automatic eye movements

Frontal Eye Fields

• Right frontal eye field

– leftward direction

• Left frontal eye field

– rightward direction

Parietal Lobes

• Control of movements in space.

– Superior regions

• Contributes to ability to produce complex, well learned motor acts.

– Inferior regions.

Parietal Lobes

• Proprioceptive information

• feedback from motor and premotor areas

Parietal Lobes

• Lesions

– superior parietal region

• lose ability to guide limbs/misreach

– Inferior parietal region

• loss of ability to perform complex acts (apraxia)

• well executed, but incorrect movements

Parietal Lobe

• Lateralization

– left inferior parietal lobe

• apraxia

Subcortical Motor Disorders

• Parkinson’s Disease

• Huntington’s Disease

• Tourette’s Syndrome

• Tardive Dyskinesia

Parkinson’s Disease

• Damage to substantia nigra (dopamine)

– 60% nerve cells

– 80% dopamine

• Tremors

• Cogwheel rigidity

• akinesia

– masked face

• postural disturbance

– shuffling, festinating gait

Parkinson’s Disease

• Treatment

– L-dopa

– grafting

Parkinson’s Disease

• Masked face

Parkinson’s Disease

• Gait

– bradykinesia

– akinesia

Parkinson’s Disease

• Gait

Parkinson’s Disease

• Gait

– dyskinesia

Parkinson’s Disease

• Gait

Parkinson’s Disease

• Hand Tremor

Huntington’s Disease

• Inherited

– 30-45 years of age

– death within 10-15 years

– 50/50 chance

• Chromosome 4

• MRI

– atrophy of caudate

• slowing

• eye-movements

• cognitive impairment

• Chorea

– jerky movements

– involuntary

– well coordinated

• bradykinesia

• eye-tracking

Tourette’s Syndrome

• Motor tics

– simple motor tics

• eyeblinks

– complex motor tics

• touching, hitting,jumping

• Vocal tics

– cries/vocalizations

• echolalia

• coprolalia

• Runs in families

• Linked to chromosome 18

• Associated problems

– OCD

– LD

– ADHD

• Treatment

– haloperidol

Cortical Motor Disorders

• Alien limb syndrome

– distal limbs

– stroke

– SMA

Apraxia

• Inability to perform skilled, purposeful movements.

– No muscle weakness

– No abnormal posture

• Observed after LH damage

• Classification Schemes

– body part

– complexity of movement

– objects vs no objects

Body Parts

• Oral (buccofacial) apraxia

– left frontotemporal

• Limb apraxia

– left parietal/parietotemporal

Complexity of Movement

• Ideational Apraxia

– form “idea” of movement

– sequence of movement

• light candle

• Ideomotor Apraxia

– disconnection between idea of movement and its execution

– can’t perform simple movements

Spatial “apraxia” (RH)

• Constructional apraxia

• Dressing apraxia

Callosal apraxia

• Disconnection syndrome

– can’t manipulate objects in left hand in response to verbal commands

Object recognition

• Ventral stream

– “what”

• Dorsal stream

– “where”

Ventral stream

• Occipital

• Occipitotemporal

• Temporal

• Devoted to processing visual information.

• Single-cell recordings.

Ventral stream

• Simple = posterior (occipital)

• Complex = anterior (temporal)

• V2: color, texture, length

• Inferotemporal

– hands or faces

• Inferotemporal

– changes in retinal position

Ventral stream

• Receptive field

– larger for anterior regions than for posterior regions.

• Sensitive to color

– figure-ground separation

Visual agnosia

• Impaired recognition of visual object

– no basic visual processing deficit

– no pervasive memory disorder

– modality specific

Apperceptive agnosia

• Can’t bind visual info together to perceive a meaningful whole.

• Basic visual processing intact (lines, light/dark)

• Posterior right hemisphere

Associative agnosia

• Perception cannot be linked to stored knowledge.

• Bilateral at occipitotemporal border.

Major differences

• Detail

– “pig” example