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This event-related functional MRI study examines the neural correlates of vibrotactile sensation within the context of different psychophysical demands. Nine subjects received vibrotactile stimuli on the right volar forearm during detection, localization, and passive tasks. In the detection task, subjects indicated the offset (end) of each stimulus by pressing a response key with their left hand. In the localization task, subjects identified the location of the stimulus ("distal?" or "proximal?") by pressing the appropriate response key 4 s after the end of the stimulus. In the passive task, subjects received the same vibrotactile stimuli, but no response was required. Analysis of stimulus-evoked activity compared with the resting baseline period revealed significant bilateral secondary somatosensory cortex activation for all three tasks. However, only in the offset-detection and localization tasks was stimulus-evoked activation observed in other expected areas of tactile processing, such as contralateral primary somatosensory cortex neighboring the posterior parietal cortex (SI/PPC) and in bilateral anterior insular cortex (aIC). During the localization task, we identified vibrotactile-evoked activation in the right aIC, which was maintained after the termination of the stimulus. Results suggest that vibrotactile-related activation within SI/PPC and aIC is enhanced by the increased levels of attention and cognitive demands required by the detection and localization tasks. Activation of aIC not only during vibrotactile stimulation, but also during the poststimulus delay in the localization trials, is consistent with the growing literature linking this area with the perception and short-term memory of tactile information.

Attenuation of responses to repeated sensory events has been thoroughly studied in many modalities; however, attenuation of pain perception has not yet benefitted from such extensive investigation. Described here are two psychophysical studies that examined the effects of repeated exposure to thermal stimuli, assessing potential attenuation of the perception of pain and its possible spatial specificity. Twenty-two subjects were presented thermal stimuli to the volar surface of the right and left forearms. Twelve subjects in study 1 received the same stimuli and conditions on each of five daily experimental sessions, whereas 10 subjects in study 2 received thermal stimuli, which were restricted to one side for four daily sessions and then applied to the other side on the fifth session. Ratings of warmth intensity, pain intensity, and pain unpleasantness were recorded while the subjects performed a thermal sensory discrimination task. Results of study 1 demonstrate that repeated stimulation with noxious heat can lead to long-term attenuation of pain perception; results of study 2 extend these findings of attenuation to both pain intensity and unpleasantness and show that this effect is highly specific to the exposed body side for both aspects of the pain experience. We suggest that the functional plasticity underlying this attenuation effect lies in brain areas with a strong contralateral pattern of pain-related activation.