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(Stroke. 1999;30:2651.)
© 1999 American Heart Association, Inc.

Original Contributions

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

A PET Study

Philippe Remy, MD, PhD; Mônica Zilbovicius, MD, PhD; Pierre Cesaro, MD, PhD; Pierre Amarenco, MD; Jean-Denis Degos, MD Yves Samson, MD

From the CEA, Service Hospitalier Frédéric Joliot (P.R., M.Z., Y.S.), Orsay; Service de Neurologie, CHU Henri-Mondor (P.R., P.C., J-D.D.), Créteil; Service de Neurologie, CHU Lariboisière (P.A.), Paris; Urgences Cérébro-Vasculaires, CHU Pitié-Salpêtrière (Y.S.), Paris, France.

Correspondence to Dr Philippe REMY, CEA, Service Hospitalier Frédéric Joliot, 4, Place du Général Leclerc, 91401 Orsay Cedex, France. E-mail remy{at}shfj.cea.fr

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 H₂¹⁵O 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.

Key Words: cerebral blood flow • somatosensory cortex • thalamus • tomography, emission computed • vibration

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