Single unit analysis of the human ventral thalamic nuclear group: correlation of thalamic "tremor cells" with the 3-6 Hz component of parkinsonian tremor

Abstract

Although cells firing at tremor frequency, called "tremor cells" (Guiot et al., 1962), have often been recorded in the thalamus of parkinsonian patients, the extent of correlation between these spike trains and tremor has rarely been assessed quantitatively. This paper describes spectral cross-correlation functions calculated between the activity of "tremor cells" and electromyogram (EMG) signals recorded from several muscles in the contralateral arm. The power occurring in the spike train at tremor frequency was described in absolute terms by the spike autopower, and in relation to the average for all spectral components by the spike autopower signal-to-noise ratio (spike autopower SNR). The probability of significant cross-correlation between the thalamic spike train and EMG at tremor frequency was assessed by the coherence at tremor frequency. Autopower spectra of the activity of many of these cells exhibited a concentration of power at tremor frequency, indicated by spike autopower SNRs as high as 18. Of the EMG signals studied, signals recorded from finger flexors were most often significantly correlated at tremor frequency. Significant correlation between the thalamic spike train and finger flexor EMG activity was found in 34% of cells analyzed. Tremor frequency coherence was significantly correlated with tremor frequency spike autopower (r = 0.46, p less than 0.0001) and spike autopower SNR (r = 0.533, p less than 0.0001). The proportion of cells with a spike autopower SNR greater than 2 that were significantly correlated with finger flexor EMG activity was greater than that of cells with a spike autopower SNR of less than 2 (p less than 0.001; chi-square). Therefore, cells exhibiting a large amount of power at tremor frequency were those best correlated with EMG activity during tremor. Some of these cells may be involved in the generation of tremor.

Thalamic Neuronal Activity in Dopamine-Depleted Primates: Evidence for a Loss of Functional Segregation within Basal Ganglia Circuits

“…Tremor may therefore occur when correlated activities turn into synchronized oscillations that spread over the cerebellar thalamus. Such an interpretation is consistent with studies of PD patients showing that pallidal synchronized oscillations are limited to tremor episodes (Levy et al, 2002), that tremor-related oscillations occur in the cerebellar thalamus (Lenz et al, 1988), and that tremor is improved by highfrequency stimulation of the cerebellar thalamus (Koller et al, 2000).…”

Dynamics of tremor-related oscillations in the human globus pallidus: A single case study

“…One possibility is that tremor-related activity is generated in a globally synchronous manner by the motor thalamus (8,10) and is transmitted to the globus pallidus. The plausibility of a thalamic origin is supported by the presence of tremorrelated activity in the motor thalamus (4,(12)(13)(14). This activity has been proposed to result from a low-threshold calcium current in thalamocortical neurons that can sustain an oscillation in membrane potential and can be triggered by hyperpolarizing input from the globus pallidus (8,10).…”

“…Several lines of evidence support this hypothesis. First, tremor-related neural activity has been observed in the motor thalamus (4,(12)(13)(14) and the posteroventral globus pallidus (11). Second, tremor is effectively ameliorated by making a lesion in the motor thalamus.…”

Selective Attenuation of Afferent Synaptic Transmission as a Mechanism of Thalamic Deep Brain Stimulation-Induced Tremor Arrest

“…Characteristic cell types such as voluntary, kinaesthetic, or tactile were identified by their response properties (Kiss et al, 2003b). Tremor cells were recognized by their burst firing pattern and their relation to observed tremor (Lenz et al, 1985(Lenz et al, , 1988(Lenz et al, , 1990(Lenz et al, , 1994. Microstimulation was applied with a monophasic constant-current stimulus isolator (A360 and A310; World Precision Instruments) in combination with a stimulus generator (these are the components that make up the ARS Neurosystem-2, Microelectrode guided neurosurgical system; Atlantic Research Systems, Atlanta, GA).…”

“…Intraoperative microelectrode recordings in the thalamus have revealed neurons that fire in bursts synchronous with electromyographic (EMG) tremor (Lenz et al, 1988). Thalamic lesions are most effective when made in the ventrolateral (VL) nucleus in regions containing these "tremor cells" (Lenz et al, 1995).…”