Cortical Processing of Noxious Somatosensory Stimuli in the Persistent Vegetative State

The persistent vegetative state (PVS) is a devastat- ing medical condition characterized by preserved wakefulness contrasting with absent voluntary in- teraction with the environment. We used positron emission tomography to assess the central process- ing of noxious somatosensory stimuli in the PVS. Changes in regional cerebral blood flow were measured during high-intensity electrical stimula- tion of the median nerve compared with rest in 15 nonsedated patients and in 15 healthy controls. Evoked potentials were recorded simultaneously. The stimuli were experienced as highly unpleasant to painful in controls. Brain glucose metabolism was also studied with ( 18 F)fluorodeoxyglucose in resting conditions. In PVS patients, overall cerebral me- tabolism was 40% of normal values. Nevertheless, noxious somatosensory stimulation-activated mid- brain, contralateral thalamus, and primary somato- sensory cortex in each and every PVS patient, even in the absence of detectable cortical evoked po- tentials. Secondary somatosensory, bilateral insu- lar, posterior parietal, and anterior cingulate corti- ces did not show activation in any patient. Moreover, in PVS patients, the activated primary somatosensory cortex was functionally discon- nected from secondary somatosensory, bilateral pos- terior parietal, premotor, polysensory superior tem- poral, and prefrontal cortices. In conclusion, somatosensory stimulation of PVS patients, at inten- sities that elicited pain in controls, resulted in increased neuronal activity in primary somatosen- sory cortex, even if resting brain metabolism was severely impaired. However, this activation of primary cortex seems to be isolated and dissociated from higher-order associative cortices. © 2002 Elsevier