Primary Somatosensory Cortex Activation Is Not Altered in Patients With Ventroposterior Thalamic Lesions

Abstract

Background and Purpose-We know remarkably little about the mechanisms underlying cortical activation. Such mechanisms might be better understood by studying the effect of well-localized lesions on the cortical activations in simple paradigms. Methods-We used H 2 15 O and positron emission tomography to measure regional cerebral blood flow (rCBF) at rest and during hand vibration in 7 patients with unilateral thalamic lesion involving the ventroposterior (VP) somatosensory thalamic relay nuclei. We compared the results with those obtained in 6 patients with thalamic lesions sparing the VP nuclei and 6 healthy controls. Results-The patients with VP lesions had a selective hypoperfusion at rest in the ipsilesional primary sensorimotor cortex (SM1). This hypoperfusion was significantly correlated with the degree of contralateral somatosensory deficit. This abnormality may reflect the deafferentation of SM1 from its somatosensory thalamic input. Despite this deafferentation, the ipsilesional SM1 was normally activated by the vibration of the hypesthetic hand. Conclusions-The fact that a lesion of the somatosensory thalamic relay nuclei alters the rCBF at rest in SM1 but not its activation by hand vibration indicates that the mechanism of cortical activation is complex, even in the case of simple sensory stimulation. In addition, a dissociation may occur between obvious neurological deficits and apparently normal activation patterns, which suggests that activation studies should be interpreted cautiously in patients with focal brain lesions. (Stroke. 1999;30:2651-2658.)

Somatosensory Gating and Recovery From Stroke Involving the Thalamus

“…There are 2 main findings: (1) Lesions involving the ventroposterior group of thalamic relay nuclei did not eliminate cortical activations associated with tactile stimulation of the strokeaffected hand, similar to the results of Remy et al 10 ; and (2) despite this unaffected primary representation, ipsilesional SI activation was abolished in all 4 patients with bilateral tactile stimulation early after stroke. Reversal of this attenuation was associated with recovery over time.…”

“…In particular, in a series of 7 thalamic stroke patients, Remy et al 10 reported a reduction in resting regional blood flow in SI but not in response to hand vibration associated with lesions in the ventroposterior nuclei. The patients reported here (except perhaps patient 4) all had small lesions affecting the ventroposterior nuclei.…”

Recovery mechanisms of somatosensory function in stroke patients: implications of brain imaging studies

“…Sii, located in the parietal operculum adjacent to the dorsal insula, has been shown to connect directly with the thalamus through thalamocortical pathways without a relay in Si [47][48][49][50][51][52][53] . in addition, bilateral receptive fields of Sii respond to both contra-and ipsilateral stimuli [35,53] and to callosal connections from the Sii area of the opposite hemisphere [54] .…”

Tactile Discrimination Task Not Disturbed by Thalamic Stimulation

“…Unlike many other studies on the role of sensory nuclei of the thalamus in sensation, we did not use simple sensory stimuli like median nerve or finger electrical stimulation [5,6,[8][9][10][11], but relied on more cognitive tasks to test the patients' performance under thalamic stimulation. Moreover, the stimuli were designed so that the subjects could not use a three-dimensional shape and could not use stereognosis, but had to rely mostly on fine touch.…”

“…Previous studies on the role of the human thalamus in sensation have focused on very simple tests like median or tibial nerve electrical stimulation or finger vibration [5][6][7][8][9][10][11][12][13]. Yet, in another set of experiments, general behavioral and psychological performance of patients in whom the thalamus is somehow involved was investigated [14][15][16][17][18].…”