No abstract

The authors present a young boy with severe generalized dystonia treated with bilateral simultaneous pallidotomy. Microelectrode recordings with the patient under propofol anesthesia showed that the mean discharge rate of globus pallidus internus (GPi) neurons was between 21 and 31 Hz. This contrasts sharply with the mean GPi neuronal firing rates of approximately 80 Hz that are characteristic of Parkinson's disease. The patient had no immediate benefit from surgery, but a progressive improvement in both axial and limb dystonia began within 3 days. The Burke-Fahn-Marsden scores were 75 (maximum possible = 120) at baseline, 52 at 5 days, and 16 at 3 months after surgery. The mechanism of action of pallidotomy for dystonia and the reasons for the delayed and progressive improvement are unknown. Nevertheless, the magnitude of the improvement and the safety of the procedure in this one patient warrant a careful evaluation of pallidotomy for dystonia.

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.