[Effect of cryosurgery of the thalamic nuclei on somatosensory evoked potentials]

Somatosensory evoked potentials were recorded in two groups of patients with extrapyramidal syndromes including: 1) parkinsonian syndromes, 2) spasmodic torticollis. In the first group stereotactic lesions were produced at the borderline between VOp and Vim nuclei, and in the second group they were situated in VOa and VOi thalamic nuclei. Short-latency components of the potentials were analysed assuming that they were the specific parts of the somatosensory potential and their value was doubtless, in contrast to the late latency components. It was found that stereotaxic lesions the VOa and VOp thalamic nuclei caused no disappearance of the short-latency potentials but reduced their amplitude. In cases with oscillation potentials recorded before the operation, they disappeared after the operation and this disappearance was correlated with clinical improvement.