THALAMUS

Rostral

Caudal

Thalamic connections of the primary motor cortex (M1) of owl monkeysIwona Stepniewska, Todd M. Preuss, Jon H. Kaas Ph.D.*

• Fluorescent tracers and wheatgerm agglutinin/horseradish peroxidase conjugate (WGA-HRP).

• The strongest connections of M1 are with subdivisions of the ventral lateral thalamus (VL); other connections are mainly with intralaminar nuclei (the central lateral, paracentral, and center median nuclei) and the reticular nucleus.

• Most projections are reciprocal and topographically organized. M1 is strongly connected with the principal (VLp), medial (VLx), and anterior (VLa) subdivisions of the VL complex but has at most weak connections with the dorsal division (VLd).

•The connections are somatotopically organized such that the M1 hindlimb representation is connected with a band of cells in the lateral and anterior portions of the VL complex (spanning VLa and VLp), whereas the trunk, forelimb, and face representations are connected with successively more medially and posteriorly situated cell bands (spanning VLa, VLp, and VLx).

RostralCaudal

VL thalamus

Medial

Lateral

• There is some degree of overlap between the somatotopic territories within VL, although the absence of double-labeled cells in cases with injections of adjacent somatotopic divisions of M1 suggests that individual thalamic neurons project to single somatotopic regions.

• In addition to somatotopic differences, the connections of the caudal and rostral subdivisions of M1 differ to some extent. Caudal M1 is connected most strongly with VLp, a target of cerebellar projections, but it is also connected with VLa, which receives pallidal inputs.

• In complementary fashion, rostral M1 is most strongly connected with VLa, but it is also connected with VLp. VLx, a target of cerebellar projections, has significant connections with both caudal and rostral M1.

Thalamic connections of the primary motor cortex (M1) of owl monkeysIwona Stepniewska, Todd M. Preuss, Jon H. Kaas Ph.D.*

http://www.neuroanatomy.wisc.edu/coursebook/thalamus.pdf

ALS – Anterolateral system (Pain from periphery)TTT – Trigeminal thalamocortical tract (Pain from face, neck etc) STT – Spino-thalamic tract (type of ALS)

Meso-corticol dopamine pathway& Serotonin Pathway

http://www.macalester.edu/psychology/whathap/UBNRP/parkinsons/corto-basal%20loop.html

Cortex (stimulates) → Striatum (inhibits) → "SNr-GPi" complex (less inhibition of thalamus) → Thalamus (stimulates) → Cortex (stimulates) → Muscles, etc. → (hyperkinetic state)

Cortex (stimulates) → Striatum (inhibits) → GPe (less inhibition of STN) → STN (stimulates) → "SNr-GPi" complex (inhibits) → Thalamus (is stimulating less) → Cortex (is stimulating less) → Muscles, etc. → (hypokinetic state)

Nigro-striatal pathway

Nigrostriatal pathway

• DOPAMINE is produced by cells in the pars compacta of the substantia nigra (SNc).

• Dopamine has an EXCITATORY effect upon cells in the striatum that are part of the Direct Pathway. This is via D1receptors.

• Dopamine has an INHIBITORY effect upon striatal cells associated with the Indirect Pathway. This is via D2 receptors.

•In other words, the direct pathway (which turns up motor activity) is excited by dopamine while the indirect pathway (which turns down motor activity) is inhibited.

•Both of these effects lead to increased motor activity.

Chollinergic interneurons -striatum

• There is a population of cholinergic(ACh) neurons in the striatum whose axons do not leave the striatum (called interneurons or local circuit neurons). • These cholinergic interneurons synapse on the GABAergic striatal neurons that project to GP(internal) AND on the striatal neurons that project to GP(external).

• The cholinergic actions INHIBIT striatal cells of the Direct pathway and EXCITE striatal cells of the Indirect pathway.

• Thus the effects of ACh are OPPOSITE the effects of dopamine on the direct and indirect pathways so the ACh effects on motor activity are opposite thoseof dopamine.

SMASMA proper: Inputs - basal ganglia via the VA thalamus, from the parietal andpremotor cortices, and from the contralateral SMA

Outputs - premotor cortex, bilaterally to the motor cortex, and to the basal ganglia, to thalamic nuclei and the brain stem and spinal cord.

Pre-SMA:Inputs - from the basal ganglia and non-motor areas of the cortex (prefrontal andtemporal)

Outputs – dorsolateral prefrontal cortex and basal ganglia

SMA – proposed functions:

Four main hypotheses have been proposed for the function of SMA: • the control of postural stability during stance or walking,• coordinating temporal sequences of actions,• bimanual coordination and • the initiation of internally generated as opposed to stimulus driven movement.

• The data, however, tend not to support an exclusive role of SMA in any one of these functions. Indeed, SMA is demonstrably active during non-sequential, unimanual, and stimulus-cued movements.

http://en.wikipedia.org/wiki/Supplementary_motor_area

Extra Reading:

PMDc (F2) PMDc is often studied with respect to its role in guiding reaching. Neurons in PMDc are active during reaching. When monkeys are trained to reach from a central location to a set of target locations, neurons in PMDc are active during the preparation for the reach and also during the reach itself. They are broadly tuned, responding best to one direction of reach and less well to different directions. Electrical stimulation of the PMDc on a behavioral time scale was reported to evoke a complex movement of the shoulder, arm, and hand that resembles reaching with the hand opened in preparation to grasp.

PMDr(F7) PMDr may participate in learning to associate arbitrary sensory stimuli with specific movements or learning arbitrary response rules. In this sense it may resemble the prefrontal cortex more than other motor cortex fields. It may also have some relation to eye movement. Electrical stimulation in the PMDr can evoke eye movements and neuronal activity in the PMDr can be modulated by eye movement.

PMVc(F4) PMVc or F4 is often studied with respect to its role in the sensory guidance of movement. Neurons here are responsive to tactile stimuli, visual stimuli, and auditory stimuli. These neurons are especially sensitive to objects in the space immediately surrounding the body, in so-called peripersonal space. Electrical stimulation of these neurons causes an apparent defensive movement as if protecting the body surface. This premotor region may be part of a larger circuit for maintaining a margin of safety around the body and guiding movement with respect to nearby objects.

PMVr(F5)PMVr or F5 is often studied with respect to its role in shaping the hand during grasping and in interactions between the hand and the mouth. Electrical stimulation of at least some parts of F5, when the stimulation is applied on a behavioral time scale, evokes a complex movement in which the hand moves to the mouth, closes in a grip, orients such that the grip faces the mouth, the neck turns to align the mouth to the hand, and the mouth opens.

CerebellumMedial Cerebellum – Vestibular andpropriospinal inputs-> Mainly controls posture

Lateral Cerebellum – inputs from cerebral cortex via basilar pontine nucleithrough mossy fibers.

Mossy fibers from red nucleus

Also climbing fibers from inferior olive complex

Motor control – Wise and Shadmehr

Descending pathways

http://www.acbrown.com/neuro/Lectures/Motr/NrMotrPrmr.htm

http://www.csuchico.edu/~pmccaffrey/syllabi/CMSD%20320/362unit7.html

http://www.cixip.com/index.php/page/content/id/1159

From M1 1) Lateral corticospinal tract2) Anterior corticospinal tract

From Red Nucleus 3) Rubrospinal tract (flexors Upper Limb)

From vestibular nuclei4) Vestibulospinal tract (extensors Lower Limb)

https://www.youtube.com/watch?v=uroOMCql1-k

Flexors

Extensors