Representation of Somatosensory Modalities in Pathways Ascending from the Spinal Anterolateral Funiculus to the Thalamus Demonstrated by Lesions in Man

Abstract

Patients with cordotomies (16), and brainstem (17) or thalamic (30) infarcts, all except cordotomies verified by magnetic resonance imaging (MRI), have been subjected to quantitative sensory perception threshold testing (QST) for touch (von Frey), mechanical pain, sharpness, innocuous warmth and cold, and heat pain in the maximally affected body area and its unaffected contralateral mirror image region. Some patients were tested twice at widely spaced time intervals; no qualitative differences were found. Results show that all modalities are dissociable from one another by lesions at all levels tested, so that there must be separable representation for each of the six modalities tested. In the lower (crossed symptoms and signs), but not the upper (uncrossed symptoms), deficits for all modalities (except for touch) were more marked than at higher levels. At the level of the thalamus, deficits for innocuous and noxious thermal modalities but not for mechanical pain were recorded in the case of lesions of the principal somatosensory relay nucleus (VPL/Vc), while more medial thalamic lesions resulted in deficits for mechanical pain but not for heat pain or innocuous thermal modalities; there is a marked deficit for sharpness caused by lesions at both thalamic sites.

Allodynia in Relation to Lesion Site in Central Post-Stroke Pain

“…There was also a failure to find any correlation between site of brainstem lesion and modality/ies of sensory deficit. 6 However, our patient who experienced pain when startled by sudden and unexpected tactile or auditory stimuli had a single well-defined pontine lesion (Fig 5), as had the case described by Watson and Colebatch. 14 Jankelowitz and Colebatch 11 state that "symptomatic increased startle occurred only in pontine lesions."…”

“…In the cat, the center for startle has been shown to be in the pontine reticular formation, 1 and to operate through an opioidergic mechanism in the rat. 8 The deficits of superficial somatosensory function that are associated with ventroposterior thalamic lesions depend to some extent on whether the lesions are lateral (ventroposterior nucleus) or further medial (medial/intralaminar nuclei) 6 ; the former show little deficit for mechanical pain but considerable deficits for innocuous and noxious thermal stimuli, whereas more medial lesions do not affect (show little deficit for) the transmission of mechanically induced pain (skinfold pinch) or thermal modalities. Pure tactile allodynia is associated with ventrolateroposterior thalamic lesions (Fig 4).…”

Dissociation of Spinothalamic Modalities Following Anterolateral Cordotomy

“…Evidence of segregation within ascending thermal and mechanical nociceptive pathways is also provided by microstimulation studies of thalamic nuclei during deep brain stimulation surgery in humans 6 as well as in patients with lesions of the brainstem and thalamus. 5 Our patient also demonstrated a dissociation in nociceptive mechanical and heat sensation. Although a deal of interaction and processing of diverse modality-specific primary afferent inputs probably occurs in the spinal cord, 1 this case further demonstrates that there remains anatomicalfunctional segregation in broadly labelled lines within the STT.…”

Somatic Sensation and the Insular-Opercular Cortex: Relationship to Central Pain

“…Somatosensory modalities are frequently dissociated at thalamocortical as well as at lower levels [18]. …”

“…– in patients with opercular-insular lesions, all thermal thresholds – warmth, cold, warm-cool difference (limen) and heat pain – were elevated to a far greater extent in patients with CPSP than in those without, and to a greater extent than in CPSP patients with subcortical lesions [32], however, no correlation between the presence or absence of central pain could be made with respect to damage to the spinothalamocortical pathway [18, 32]. …”