REORGANIZATION OF SENSORY MODALITIES EVOKED BY MICROSTIMULATION IN REGION OF THE THALAMIC PRINCIPAL SENSORY NUCLEUS IN PATIENTS WITH PAIN DUE TO NERVOUS-SYSTEM INJURY

Stimulation of the somatosensory system is more likely to evoke pain i n patients with chronic pain after nervous system injury than in patie nts without somatosensory abnormalities. We now describe results of st imulation through a microelectrode at microampere thresholds (threshol d microstimulation; TMIS) in the region of the human thalamic principa l sensory nucleus (ventral caudal; Vc) during operations for treatment of movement disorders or of chronic pain. Patients were trained preop eratively to use a standard questionnaire to describe the location (pr ojected field) and quality of sensations evoked by TMIS intraoperative ly. The region of Vc was divided on the basis of projected fields into areas representing the part of the body where the patients experience d chronic pain (pain affected) or did not experience chronic pain (pai n unaffected) and into a control area located in the thalamus of patie nts with movement disorders and no experience of chronic pain. The reg ion of the Vc was also divided into a core region and a posterior-infe rior region. The core was defined as the region above a standard radio logic horizontal line (anterior commissure-posterior commisure line; A CPC line) where the majority of cells responded to innocuous somatosen sory stimulation. The posterior-inferior area was a cellular area post erior and inferior to the core. In both the core and the posterior-inf erior regions, the proportion of sites where TMIS evoked pain was larg er in pain-affected and unaffected areas than in control areas. The nu mber of sites where thermal (warm or cold) sensations were evoked was correspondingly smaller, so that the total of pain-plus-thermal (sensa tion of warmth or cold) sites was the same in all areas. Therefore, si tes pain where stimulation evoked pain in patients with neuropathic pa in (i.e., pain following an injury to the nervous system) may correspo nd to sites where thermal sensations were evoked by stimulation in pat ients without somatosensory abnormality. J. Comp. Neurol. 399:125-138, 1998. (C) 1998 Wiley-Liss, Inc.