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

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.