Review: General Control Theory

-Cortex-Basal Ganglia-Cerebellum

Review: Primary M. CortexDirectionality:

yellow = one cell’s firing vectors (broad)red = “best” vector

No one (1) cell can generate an appropriate directional code!Population Tuning

Motor CortexTopographical Orientation…great question from last time

Current Research TopicsConserved Topographical Organization?(Bizzi E):

PreMotor Cortex- Rostral Pre-Central Gyrus

- Activated by cues for well-learned events (monkey)

PreMotor Cortex

PreMotor Cortex Continued

Lateral PreMotor elements- conditional tasks- fire before action- external cues (in monkey anyway)- damage = inability to select appropriate response movements

Medial PreMotor elements- initiate internally / voluntarily driven motor tasks- internal cues- damage = reduced spontaneous movements

Primary vs. PreMotor

Inputs:- Premotor Cortex

- Somatosensory Cortex

Inputs:- Pre-Frontal Cortex

- Areas 5 and 7

Review

Be familiar with the contribution of each particular anatomical structure / region:

-Cortex 2 regions discussed

-Brainstem the 3 nuclei discussed & pathways

-Spinal Cord spatial significance / distribution

-Local Circuitry / MNs / Muscle those properties discussed

Basal Ganglia(Group #3)

Anatomical Components:

Globus Pallidus

Corpus Striatum (striped)

- caudate nucleus- putamen- ventral striatum

Associated Nuclei - substantia nigra- subthalamic nuclei

*

Basal Ganglia

Function

- Active before and during movements

- Inputs: majority of cortexmultiple parallel pathways

- Output: thalamus, superior colliculus, cortex… “Upper Motoneurons”

- High levels of efferent tonic inhibition

- GABAergic outputDirect Pathway: interrupt tonic inhibitionIndirect Pathway: internal loop increases inhibition

Basal Ganglia ContinuedMedium Spiny Neurons- majority of cells in striatum

75,000,000 (!)- labeled line- occur in patches: striosomes- normally not tonic

Cerebral CortexCerebral Cortex

Corpus StriatumCorpus Striatum

(caudate & putamen)(caudate & putamen)

Medium Spiny Medium Spiny

NeuronsNeurons

Globus Pallidus &Globus Pallidus &Substantia NigraSubstantia Nigra

Upper MNsUpper MNs

Globus Pallidus- 1/100 number of m. spiny neurons

750,000- INTEGRATOR- high level tonic output- GABAergic- Primary pathway back to motor cortex is via internal G. P.

Direct Pathway (tonic only)Direct Pathway (tonic only)

Normal activity of the direct pathway = hypokinesia

Direct Pathway (phasic activation)Direct Pathway (phasic activation)

Reduced activity of the direct pathway (GP) = hyperkinesia

Enhanced activity in the indirect pathway = hypokinesia

Indirect PathwayIndirect Pathway

Parkinson’s Disease

medium spiny neurons

- damage to Nigrostriatal cells

- increased thalamic inhibition- seldom can coordinate movements- bursts of activity

Parkinson’s Diseasetreatments

Must attenuate activity in the Globus Pallidus

- l-Dopa (there are several pharmacological treatments)- thalamotomy - pallidotomy

Huntington’s Disease

medium spiny neurons

- sequence is known, protein function is not - yet- genetic test is available

- excessive excitability- involuntary movements- eventual loss of mental cohesion

Huntington’s Diseasetreatments

Must augment activity in the Globus Pallidus

- ACh (acetylcholine)- Striatal tissue implants- genetic treatments (?)

http://www.macalester.edu/~psych/whathap/UBNRP/Huntington/treatmentdir.html

Cerebellum(Group #4)

Anatomical Components:

Cerebellar Cortex:- Spinocerebellum

gross movt’svermis

- Cerebrocerebellumcomplex movt’s

- Vestibulocerebellumposture / balancenodulusflocculus

Cerebellum

CerebellumAnatomical Componentscontinued:

Cerebellar Deep Nuclei: (All receive input from the cerebellar cortex – though functionally distinct)

- Dentate (invaginations)- Fastigial- Interposed (2)

Cerebellar Peduncles- Superior efferent pathways

- Middle afferent pathways

- Inferior Both afferent & efferent

Cerebellum

- inputs from:pre-motor, primary motor,primary / secondarysomatic, anterior parietal,secondary visual (not

primary)- behavior modulation inputs: “learning”

inferior olivelocus coruleus

General Function (still not completely understood)

- measure motor error- motor learning- output to cortex (via thalamus) and vestibular nucleus

Modify activity pattern of “Upper MNs”Modify activity pattern of “Upper MNs”

Cerebral CortexCerebral Cortex[Report what’s happening][Report what’s happening]

Pontine NucleiPontine Nuclei

[Relay / Process][Relay / Process]

Cerebellar CortexCerebellar Cortex

[Compute error(?)][Compute error(?)]

Deep Cerebellar Deep Cerebellar

NucleiNuclei

Thalamus (Cortex) Thalamus (Cortex)

&&Vestibular NucleusVestibular Nucleus

[Tell control centers][Tell control centers]

middle peduncle

Cerebellar Cell Types

(inhibitory)“control the flow of information through the cerebellar cortex”

Mossy Fibers: (excitatory)

From: - pontine nuclei (via middle peduncle)- other pons / brainstem loci

To: - deep cerebellar nuclei- granule cells

Granule Cells: (most abundant in brain)From & To: cerebellar cortex… ~unipolarGive rise to: Parallel Fibers: (excitatory)

Climbing Fibers: (excitatory)

From: - inferior oliveTo: - Purkinje shaft

Local Interneurons:- Basket Cells- Stellate Cells- Golgi Cells

Purkinje Cells: (inhibitory)

If there were a brain of the cerebellum, it would be the Purkinje cells

Cerebellar Cell Types

Extraordinarybranchingintegrative properties

Clinical ImplicationsClinical Implications

Normal Function (to reiterate):- Smooth motor functions (reduce error)- Coordinate target acquisition

Lesion or Degeneration:- Loss of smooth movements

- Rarely stop on target

CONCLUDING ADMONITIONCONCLUDING ADMONITION

The ability to successfully complete an organized sequence of movements requires

the appropriate coordination of MANY elements.

Spatial organization(rubrospinal pathways, spinal signals, cerebellar

integration)Temporal organization

(cortical planning)Accuracy and uniformity

(error measures, sensory integration)Sequencing

(spinal circuitry)