Ventralis Posterior Lateralis Research Articles

Thalamic sensory nuclear ablations in trained monkeys.

THE NEUROPHYSIOLOGICAL characteristics of the ventrobasilar complex (VB) of the thalamus have been well defined in rabbit, 1 cat, 2,3 monkey, 4-9 and man. 10,11 Somatotrophic localization is manifest by representation of the face in ventralis posterior medialis (VPM), with the arm, trunk, and leg extending from the medial to lateral portions of ventralis posterior lateralis (VPL). Each body part is represented by a lamellar group of cells; the distal parts of the limbs are represented ventrally and the axial portions dorsally; thoracic and lumbar areas are represented only dorsally. The number of thalamic cells activated from the body surface is proportional to the number of sensory receptors in that area. This pattern of topographic localization has been confirmed in man during the course of stereothalamotomies for movement disorders. 12 In man there may also be a second somatotrophically organized area in VB, located posteriorly and oriented vertically to

The specific somatosensory system and dyskinesia.

SEVERAL hypotheses have been proposed for the mechanism of abnormal movements, with the greatest emphasis placed upon the role of central structures. 1-3 While the importance of muscle afferents has also been stressed, 4 little attention has been paid to other peripheral receptors. However, observations made during a series of stereotactic thalamotomies suggest that impulses transmitted over the specific somatosensory pathways are also concerned in dyskinesia. Materials and Methods Cortical and subcortical potentials evoked by transcutaneous electrical stimulation of the median nerve were recorded during 42 stereotactic thalamotomies in patients with dyskinesia. The cortical responses were detected by pin electrodes placed in the scalp, and the depth responses by concentric, bipolar, Teflon insulated, stainless steel electrodes with an outer diameter of 1.4 mm and tip separation of 0.5 mm. An averaging computer was used to retrieve the evoked potentials. 5 The electrodes were directed toward nucleus ventralis posterior lateralis

Evoked potential recording: an adjunct to human stereotactic surgery.

The localization of various brain structures during stereotactic surgery is dependent upon stereotactic atlases used in conjunction with demonstrable radiographic landmarks. Because of the considerable anatomical variability encountered in humans, this localization is only an approximation. For animal studies electrode positions can be confirmed histologically at necropsy. Routine techniques have been developed for animal neurophysiologic recording but have not been extensively applied to humans. This paper presents a method for recording human evoked potentials from various thalamic nuclei. Peripheral stimulation and stimulation within the brain are used to evoke depth and scalp potentials. The evoked responses are averaged at various well-known thalamic nuclei, e.g., ventral posterior lateral (VPL), ventral posterior medial (VPM), centre median (CM), that have characteristic responses. These nuclei, in conjunction with radiographic information, are used as landmarks to aid location of other brain structures.

Aggressive Behavior Evoked by Radio Stimulation in Monkey Colonies

Macaca mulatta with multilead electrodes permanently implanted in the brain were electrically stimulated, either under restraint, or by radio while moving freely as part of a colony, in which case individual and social behavior were recorded, analyzed, and quantified with the aid of time-lapse photography. Some cerebral radio stimulations evoked complex sequences of well organized responses. Increase in running and in offensive behavior was produced by excitation of midline thalamus, while even faster running without changes in aggressiveness was produced by stimulation of the fimbria of the fornix. Conditioning was absent in the first case, but it was easily established in the latter. Increase in aggressive behavior was also produced by stimulation of Forel's field, the nucleus ventralis posterior lateralis of the thalamus, and the central gray matter. Increase in aggressiveness was oriented by the animal according to past experience, likes and dislikes, and was adapted to the changing strategies of its opponent, indicating an excellent processing of sensory information, and demonstrating that brain stimulation had induced a “drive” and not a stereotyped motor response. As a working hypothesis it is proposed that cerebral mechanisms for perception of pain and for aggressive behavior have different anatomical and physiological systems closely interrelated by use, disuse, and conditioning.

Electrophysiological studies of some deep cerebral structures in man

In stereotactic operations for Parkinson's disease and other disturbances of voluntary movement, the electrophysiological activity of the brain was recorded along the trajectory of the coagulating electrode. The method permitted a clear distinction between white matter and gray matter. Within the thalamus and elsewhere it was possible to differentiate functionally the activity of numerous nuclei (pulvinar, lateralis posterior, ventrolateralis, ventralis posterior medialis and lateralis, globus pallidus, amygdala). Somato-topically organized potentials were recorded in the nucleus ventralis posterior upon natural peripheral stimulation. In several nuclei it was possible to observe rhythmical activities occurring at the same frequency as the muscle tremor. These activities must have been the result of the muscle tremor in some thalamic structures (ventralis posterior lateralis) but they appear to be more directly related to the ‘generation’ of the tremor in other nuclei (lateralis posterior and possibly ventralis lateralis). Stimulation of thalamic and capsular sites produced sensory or motor effects fully in agreement with the results of derivation from these points. This method made it possible to improve the accuracy of the placement of the lesion and to demonstrate again the considerable anatomical variability of the individual thalamus.

Retrograde cell degeneration in diencephalic and other structures after hemidecortication of rhesus monkeys

Two newborn and three young adult monkeys ( Macaca mulatta) were hemidecorticated by surgical aspiration and allowed to survive postoperatively for 15 to 31 days. The brains were perfused, sectioned transversely and stained with thionine. Resulting retrograde cell degeneration in the diencephalon and various other structures was examined microscopically and a comparison made between the newborn and adult animals. In the infant monkeys the following thalamic nuclei showed heavy cell loss: anterior dorsalis; anterior ventralis; anterior medialis (lateral two-thirds); ventralis lateralis; ventralis posterior lateralis; ventralis posterior inferior; lateralis dorsalis; lateralis posterior; reticularis; medialis dorsalis, partes parvocellularis and multiformis; pulvinaris; geniculatus lateralis dorsalis; geniculatus medialis, pars parvocellularis; and suprageniculatus. Nuclei showing partial cell loss were: anterior medialis (medial one-third); medialis dorsalis, pars densocellularis; reuniens; centralis latocellularis; alaris; centralis lateralis; paracentralis; limitans; and ventralis posterior medialis. Unaffected or only slightly affected nuclei included: ventralis anterior; medialis dorsalis, pars magnocellularis; geniculatus medialis, pars magnocellularis; centrum medianum; parafascicularis; centralis superior lateralis; and assorted midline nuclei. Thalamic degeneration in the adults was similar to the infants with the following exceptions which showed more severe cell loss in the adults: ventralis anterior; medialis dorsalis, pars magnocellularis; geniculatus medialis, pars magnocellularis; centralis lateralis; and paracentralis. Additional degeneration was present in three extrathalamic structures: the medial mamillary nucleus, which showed severe cell loss in the infants and partial cell loss in the adults; the caudal half of the nucleus of the diagonal band of Broca, which had virtually disappeared; and the ipsilateral pontine nuclei which were partially affected in the infants. No differences in extent of degeneration could be ascribed to variation in postoperative survival times.