Abstract
On the stereotaxic thalamotomy for Parkinson's disease (PD), excess beta-band (13-27 Hz) rhythmic activities are observed in the thalamic ventroanterior/ventrolateral nuclei (VA/VL). To test the hypothesis that these activities were relevant to muscle rigidity, we analyzed their correlates in the surface electromyograms (EMGs) from limb muscles. The VA/VL beta-band activities were recorded with a bipolar concentric semi-microelectrode and observed as filtered local field potentials (beta-waves). In five PD patients who gave their informed consent to undergo the surgery with the electrophysiological examinations, we found that the VA/VL beta-waves were synchronized with limb muscle EMGs. Analysis revealed their properties as follows. 1) The beta-waves occurred when the patients became alert in a condition with increased or even rigid muscle tone spontaneously or in response to passive stretch maneuver. 2) In this condition, the beta-waves became transiently synchronized with the complex spikes in individual limb muscle EMGs. 3) During this particular period of synchronism the negative-going deflection of beta-waves with concurrent multiple unit spikes preceded the spike EMGs. 4) Active muscle contraction rarely abolished the preexistent beta-waves but rather less affected on their quantity. The results suggest that the excess VA/VL beta-band activities are contingently involved in parkinsonian rigidity by driving individual or presumably a population of muscles to contraction through the thalamocortical pathways. [Jpn J Physiol 54 Suppl:S192 (2004)]
