Thermal and pain sensations evoked by microstimulation in the area of human ventrocaudal nucleus

Abstract

1. We have studied the sensations evoked by threshold microstimulation (TMS) in the area of the human principal sensory nucleus of the thalamus [ventralis caudalis (Vc)] in patients (n = 11) undergoing stereotactic surgery for the treatment of movement disorders and pain. Preoperatively, patients were trained to describe somatic sensory stimuli using a standard list of descriptors. This same list was used to describe sensations evoked intraoperatively by thalamic microstimulation. Stimulation sites (n = 216) were defined by location within the area where the majority of cells had a reproducible response to innocuous cutaneous stimulation (core region) or in the cellular area posterior and inferior to the core region (posteroinferior region). 2. TMS-evoked sensations were categorized as paresthetic if the descriptors "tingle," "vibration," or "electric current" were chosen by the patient to describe the sensation and as thermal/pain if the descriptors "cool," "warm," "warm and cool," or "pain" were chosen. Thermal/pain sensations were evoked by stimulation in 82% (9/11) of patients and at 19% of sites studied. These results suggest that thalamic microstimulation can evoke thermal/pain sensations reproducibly across patients. 3. Thermal/pain sensations were evoked more frequently by stimulation at sites in the posteroinferior region (30%) than by stimulation at sites in the core region (5%). Nonpainful thermal sensations composed the majority of thermal/pain sensations evoked by stimulation in both the core (80%) and posteroinferior regions (86%). Sites where stimulation evoked pain and nonpainful cool sensations were found anterior to the area where nonpainful warm sensations were evoked. Thermal/pain sensations were evoked at sites located medially near the border between the core and posteroinferior regions. 4. Radiologic techniques were used to determine the presumed nuclear location of stimulation sites. Thermal/pain sensations were evoked less frequently by stimulation in the part of Vc included in the core region than by stimulation in any of the following: the part of Vc included in the posteroinferior region, ventralis caudalis portae nucleus, ventralis caudalis parvocellularis nucleus, or the white matter underlying the ventral nuclear group. 5. The location of the sensation evoked by stimulation [projected field (PF)] varied widely in size. PFs were categorized as large if they involved more than one part of the body (e.g., face and arm) or if they crossed at least one joint proximal to the metacarpophalangeal joint or to the metatarsophalangeal joint. PFs were more frequently large at sites where thermal/pain sensations were evoked by TMS (33%) than at those where paresthesia were evoked (6%).(ABSTRACT TRUNCATED AT 400 WORDS)

Lesions Limited to the Human Thalamic Principal Somatosensory Nucleus (Ventral Caudal) Are Associated with Loss of Cold Sensations and Central Pain

“…Patient 8 (Vc only) showed cold allodynia in response to the brass bar, which is nonpainful in control subjects (Lenz et al, 1993a). Among three patients tested with quantitative testing, one patient had cold allodynia (patient 18), and one had hypoalgesia (patient 13).…”

“…A complete neurologic history and physical examination was performed in each case independently by a neurosurgeon and neurologist, including a detailed clinical assessment of somatic sensory function (Lenz et al, 1993a). We next examined the thresholds for innocuous warm, innocuous cool, heat pain, cold pain, and innocuous tactile sensations, as well as the presence of brushing allodynia.…”

Squirrel monkey lateral thalamus. I. Somatic nociresponsive neurons and their relation to spinothalamic terminals

“…Bushnell et al (1993) Recently it was reported that microstimulation in the human lateral thalamus may evoke "cool" and "warm" perceptions (Lenz et al, 1993a). Lenz et al (1993b) have now been able to record from three cooling responsive cells in the lateral thalamus ofthe awake human.…”

“…More recently, recordings and microstimulation were performed in the lateral thalamus of chronic pain or motor disorder patients (Lenz et al, , 1988(Lenz et al, , 1993aTasker et al, 1987;Dostrovsky et al, 199 1). These studies indicate the existence of a lateral thalamic region, just ventral and posterior to the main somatosensory nucleus, the stimulation of which results in localized contralateral thermal or @ain reports in unanesthetized subjects, and single-unit recordings show a small number of cells with activity correlated with noxious stimulation.…”

Different Pain, Different Brain: Thalamic Anatomy in Neuropathic and Non-Neuropathic Chronic Pain Syndromes

“…Similar to CPSP, neuropathic pain after spinal cord injury is associated with thalamic anatomical changes, the extent of which is correlated with pain intensity (Apkarian et al, 2004;Gustin et al, 2010). Furthermore, VP thalamic stimulation can produce pain (Lenz et al, 1993;Davis et al, 1996) and increased thalamic bursting activity and biochemical changes indicative of neuronal loss occur in patients with pain after spinal cord injury (Lenz et al, 1989;Pattany et al, 2002). In direct contrast to neuropathic pain conditions, pain associated with temporomandibular disorders (TMD) results primarily from the activation of peripheral nociceptors (Sarlani and Greenspan, 2005;Ro, 2008;Sessle et al, 2008;Manfredini and Nardini, 2010) and, furthermore, is associated with thalamic gray matter volume increases (Younger et al, 2010).…”