Single Unit Analysis of the Human Ventral Thalamic Nuclear Group

Abstract

During neurosurgical operations for the relief of movement disorders, single thalamic neurons (n = 107) were identified with activity which was related to verbally cued active movements (movement-related cells). The activity of each neuron was examined during different contralateral movements in order to determine the movement which was associated with the most consistent and pronounced change in firing rate (the optimal response). The optimal response was determined by analysis of histograms of neuronal activity which were constructed by using the onset of EMG activity to synchronize successive repetitions of the active movement. Movement-related cells exhibited optimal responses associated with such movements as making a fist, extension or flexion of the wrist, flexing or extending the elbow, pointing with the entire upper extremity, extending the tongue and lifting the leg. Most movement-related cells recorded in a single parasagittal plane in an individual patient had optimal responses related to movements involving the same part of the body. Movement-related cells were classified into those that were activated in response to somatosensory stimulation (combined cells, n = 20) and those which were not (voluntary cells, n = 87). Combined cells were activated in advance of EMG activity during active movement and so could be distinguished from cells responding only to sensory stimulation (sensory cells). Movement-related cells (combined and voluntary cell types) were located anterior to sensory cells and tended to show a mediolateral somatotopic organization parallel to that of sensory cells with cutaneous receptive fields. Combined cells responded to somatosensory stimulation of the same part of the body as that involved in the active movement related to the optimal response of the cell. Combined cells responding to passive movements of a joint always had their optimal response during active movement about the same joint. The activity of combined cells during parkinsonian tremor may clarify the role of sensory feedback in tremor.

Difference in surgical strategies between thalamotomy and thalamic deep brain stimulation for tremor control

“…They emphasized that tremor is arrested in an almost point-to-point relation between coagulation of these cells and control of tremor within their receptive field. On the other hand, Lenz et al [13] found that a small radiofrequency lesion within an area where the majority of cells are not responsive to a passive joint movement [6,9,22,25,32] provided an excellent effect on tremor.…”

The pathophysiology of parkinsonian tremor: a review

“…Anterior to the Vc is the motor thalamus with the Vim and the Vop, and this area contains cells firing in response to voluntary movement (voluntary cells) and cells which respond both to movement and somatosensory stimulation (combined cells). Tremor cells have been found among the sensory, voluntary and combined cells [89,93]. Lenz et al demonstrated that voluntary and combined cells do usually exhibit phase advance suggesting an efferent role for this firing and that sensory cells exhibit a phase lag suggesting an afferent relay function for this cell group.…”

Statistical prediction of the optimal site for thalamotomy in parkinsonian tremor

“…All cells analyzed in this article were located in or adjacent to the region where cells exhibited activity related to active movements of the upper extremity as determined by techniques used in previous studies (26,34). It is in this region that many single units are significantly correlated with EMG activity during tremor (16,25,26).…”