The document summarizes research on the thalamic connections of the primary motor cortex in owl monkeys. Three key findings are:
1) The strongest connections are between M1 and subdivisions of the ventral lateral thalamus, particularly the principal, medial, and anterior subdivisions.
2) The connections are topographically organized such that different body part representations in M1 connect to distinct bands within the thalamus.
3) While caudal M1 connects strongly with the principal subdivision, rostral M1 connects more with the anterior subdivision.
3. Thalamic connections of the primary motor cortex (M1) of owl monkeys
Iwona 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
4. • 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 monkeys
Iwona Stepniewska, Todd M. Preuss, Jon H. Kaas Ph.D.*
11. 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.
12. 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 those
of dopamine.
13. SMA
SMA proper:
Inputs - basal ganglia via the VA thalamus,
from the parietal and
premotor 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 and
temporal)
Outputs – dorsolateral prefrontal cortex and
basal ganglia
14. 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
15.
16. 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.
17. Cerebellum
Medial Cerebellum – Vestibular and
propriospinal inputs
-> Mainly controls posture
Lateral Cerebellum – inputs from
cerebral cortex via basilar pontine nuclei
through mossy fibers.
Mossy fibers from red nucleus
Also climbing fibers from inferior olive
complex
Just the basic locations of various regions of the cortex. Break down supplementary cortex, premotor and frontal eye field as well as posterior parietal cortex.
Which inputs into thalamus affect inputs to M1. there are inputs from basal ganglia and cerebellum. Also there are indirect effect of cortical inputs to basal ganglia.
