The Thalamus in the Motor System

Abstract

The ventrolateral (VL) and ventral anterior (VA) are the main thalamic relay for cerebellar and pallidal efferents going to the motor cortex. Four aspects of the function of these nuclei are briefly considered. (1) It is well known that these thalamic structures are not a simple relay on the way to the motor cortex, but that they have a gating function for the cerebellar afferents. The gating mechanism is active during slow-wave sleep, with deafferentation and with the use of various anesthetics. Possibly, it might play a role in the central organization of movement. (2) The organization at the unitary level of the projections between VL and motor cortex is examined and their role in the command of motor synergies through the motor cortex strongly suggested. (3) It appears that unitary activity of VL neurons is not only related to movement but also to postural changes associated with movement. (4) The sensory input to VL nucleus is briefly analyzed. The inefficacy of exteroceptive stimulation in awake animals, in contrast with the effect of the same stimulation in anesthetized preparations, is discussed.

Neural aspects of anticipatory behavior

“…Purpura (1970) suggested that this eect can be described as a functional deaerentiation. The local inhibitory in¯uence of the RN in the motor domain has also been described by Massion (1967), who considered the thalamic motor nuclei a gate that might be open or closed to a motor command.…”

Bilateral Improvement in Voluntary Movement after Unilateral Diencephalic Lesions for Parkinsonism

“…A diencephalic lesion may affect contralateral limbs through bulbo spinal fibers [4,5,10,13,15,16] or by projections from VL thalamus, through the overlying cortex, to the contralateral spinal cord [19,27], The lesion may have an ipsilateral effect mediated through uncrossed de scending projections (corticospinal [24,34] or bulbospinal [5,13,15,16] fibers): alternatively the lesion may affect motor mechanisms on ¡he other side of the brain [5,6,14,20,29,36] which in turn exert a (crossed) in fluence on segmental neurons ipsilateral to the lesion. In particular, the lesion could exert bilateral effects through connections within the brain stem that link the two sides of the reticular formation and through others linking the basal ganglia and thalamus on one side of the brain with sub cortical structures on the other [5,12,18,23,28,30,32], Patients improved in using the arm ipsilateral to surgery, although there was no obvious improvement in its tremor or rigidity.…”

“…Moreover, for the drawing test, the lesion's initial effect (during pre5/ postl) was to improve the contralateral arm more than the ipsilateral one, whereas, for the pegboard test, the contralateral arm tended to be worse directly after surgery while the ipsilateral arm was unchanged. This initial deterioration in timed performance of the contralateral arm was associat ed with a transient dysmetria clinically apparent in some patients while using the limb for the pegboard test on postl, and presumably reflecting a disturbance of pathways that carry proprioceptive and visual feedback to the thalamus and motor cortex [3,7,19,22]. Such a disturbance of coor dination would affect performance with the pegboard rather than the bal listic movement involved in the drawing test.…”

Changes in the spike activity of neurons in the ventrolateral nucleus of the thalamus in humans during performance of a voluntary movement

“…The properties of the neurons which we designate as type A are similar to those described [1,6,8,12,[19][20][21]23] for "motor" neurons in the ventrobasal complex of the human thalamus, which respond to the performance of voluntary movements, and have been called "voluntary movement" cells [9]. The involvement of these elements of the ventrolateral nucleus of the thalamus in transmitting information during processing of conditioned reflex operant movements is also indicated by results obtained in animal experiments [7,11,14,15,22].…”

“…The appearance of dynamic cross-correlation relationships between close-lying neurons in these functional stages of voluntary movements can evidently be taken to support the existence of an interaction between cellular elements. Considering the close morphological connections of the ventrolateral nucleus [10,14,16,18] with the cerebral cortex, with underlying subeortical structures, and intralaminar formations, it can be suggested that the multicomponent patterns of network activity of A and B cells reflect their simultaneous complementary responses to facilitation and/or inhibition of influences from different sources arising during performance of a voluntary movement. It was typical that the interconnected changes in activity in both kinds of ceils did not correlate with the performance of any particular movement, its type, or somatotopic properties.…”