LOW-THRESHOLD CALCIUM SPIKE BURSTS IN THE HUMAN THALAMUS - COMMON PHYSIOPATHOLOGY FOR SENSORY, MOTOR AND LIMBIC POSITIVE SYMPTOMS

Positive symptoms arise after lesions of the nervous system. They incl ude neurogenic pain, tinnitus, abnormal movements, epilepsy and certai n neuropsychiatric disorders. Stereotactic medial thalamotomies were p erformed on 104 patients with chronic therapy-resistant positive sympt oms. Peroperative recordings of 2012 single units revealed an overwhel ming unresponsiveness (99%) to sensory stimuli or motor activation. Am ong these unresponsive cells, 45.1% presented a rhythmic or random bur sting activity. Rhythmic bursting activities had an average interburst interval of 263+/-46 ms corresponding to a frequency of 3.8+/-0.7 Hz. Frequency variations among the different symptoms were not statistica lly different. Intraburst characteristics such as the highest frequenc y encountered in the burst (480+/-80 Hz) or the mean frequency of the burst (206+/-44 Hz) were also similar in all patients. All bursts, rhy thmic or random, fulfilled the extracellular criteria of low-threshold calcium spike (LTS) bursts. After medial thalamotomy and depending on the symptom, 43-67% of the patients reached a 50-100% relief with spa ring of all neurological functions. On the basis of these electrophysi ological and clinical results, we propose a unified concept for all po sitive symptoms centred on a self-perpetuating thalamic cell membrane hyperpolarization, similar to the one seen in slow-wave sleep.