Analysis of non-parkinsonian tremor with complicated pathophysiology viewed from brain activities monitored during thalamotomy

Abstract

Background: In the procedure of thalamotomy, we mark the targets by thalamic 13-27-Hz β-band and 3-7-Hz τ-range hyperactivities as representing parkinsonian rigidity and tremor, respectively. Aim: We tested the validity of these thalamic markers in surgically treated non-parkinsonian patients with tremor of complicated pathophysiology. Methods: As the cases with tremor, but no thalamic τ-range hyperactivities, we selected four of the 23 previously studied non-parkinsonian patients; examined the shoulder, neck, face and limb electromyograms, brain local field potentials, and multiple unit spikes; and rated the local field potentials in the bands of 3-7, 7-13, 13-27 and 27-80 Hz. Results: Tremor rated as moderate in the present study was postural, kinetic, intentional, ballistic, or myoclonic, or of some combined nature with irregular rhythms at variable frequencies widely ranging in 1-13 Hz. Tremor accompanied motor hyperactivities and thalamic β-band hyperactivities, but not τ-range activities. The β-band hyperactivities and high neural noise occurred in the caudate nucleus, thalamic ventroanterior nucleus, nucleus ventralis lateralis and nucleus ventralis intermedius. The thalamic β-band hyperactivities were not accompanied by rigidity in three of the patients. The four patients were thus atypical when compared with the other non-parkinsonian and parkinsonian patients. Yet, thalamotomy alleviated tremor and concurrent motor hyperactivities. Conclusion: Non-parkinsonian tremor in the four patients was related to β-band hyperactivities, and elevating neural noise in wide regions of the basal ganglia and thalamus. Thalamotomy was effective by eventually abolishing ventralis lateralis with β-band hyperactivities and high noise that was involved as a part of the widely distributed pathophysiology of these patients.