Localization in human thalamus of units triggered during 'verbal commands,' voluntary movements and tremor

Microelectrode recordings in the rostral (n. reticularis) and lateral (ventralis lateralis) human thalamus were carried out in locally anaesthetized diskinetic patients during stereotaxic operations. Their responses to voluntary motor tasks prompted by imperative verbal stimuli were tested. Spontaneous and evoked unit activities were studied using computer processing techniques. In the n. reticularis thalami and immediately adjacent thalamic zones, not only units reacting during the initiation of voluntary movements (100-200 msec before the movement), but also units responding to the verbal command itself ('triggered verbal command' units) were found. They proved to be concerned directly with the semantic meaning of the command. In the VL anterior area (Voa-Vop in German nomenclature) the majority of the units responded during the phases of initiation and/or realization of the voluntary motor act ('voluntary movement' units of Jasper and Bertrand 1966); when these units were not spontaneously rhythmic they were transiently transformed into rhythmic (5 +/- 1 Hz) ones. This transformation appeared during the preparation and realization of movement but also in some cells as a rebound phenomenon. In patients without tremor (akinetic and rigid forms of parkinsonism, torticollis), the transient rhythmogenic transformation was frequently provoked by the repetition of motor tasks. In the posterior part of VL (Vim), cells were driven by proprioceptive inflow coming from a specific peripheral region. They react also during the voluntary movement of the same region. The majority of these units were rhythmic at 5 +/- 1 Hz, and they presented a close correlation in phase and frequency with the tremor. The anatomical locations of the three main pools of neurons were determined. 'Triggered verbal command' units were placed more anteriorly and laterally. 'Voluntary movements' and 'rhythmic 5 +/- 1 Hz units' had identical spatial localizations. This fact supports the contributions of these two last types to the central mechanisms of both tremor and voluntary movement.