Recordings of event-related potentials (ERPs) were combined with structural and functional magnetic resonance imaging (fMRI) to study the spatio-temporal patterns of cortical activity that underlie visual–spatial attention. Small checkerboard stimuli were flashed in random order to the four quadrants of the visual field at a rapid rate while subjects attended to stimuli in one quadrant at a time. Attended stimuli elicited enhanced ERP components in the latency range 80–200 ms that were co-localized with fMRI activations in multiple extrastriate cortical regions. The earliest ERP component (C1 at 50–90 ms) was unaffected by attention and was localized by dipole modeling to calcarine cortex. A longer latency deflection in the 150–225 ms range that was accounted for by this same calcarine source, however, did show consistent modulation with attention. This late attention effect, like the C1, inverted in polarity for upper versus lower field stimuli, consistent with a neural generator in primary visual cortex (area V1). These results provide support to current hypotheses that spatial attention in humans is associated with delayed feedback to area V1 from higher extrastriate areas that may have the function of improving the salience of stimuli at attended locations.

Although feeling pain and touch has long been considered inherently private, recent neuroimaging and neurophysiological studies hint at the social implications of this experience. Here we used somatosensory-evoked potentials (SEPs) to investigate whether mere observation of painful and tactile stimuli delivered to a model would modulate neural activity in the somatic system of an onlooker. Viewing video clips showing pain and tactile stimuli delivered to others, respectively, increased and decreased the amplitude of the P45 SEP component that reflects the activity of the primary somatosensory cortex (S1). These modulations correlated with the intensity but not with the unpleasantness of the pain and touch ascribed to the model or the aversion induced in the onlooker by the video clips. Thus, modulation of S1 activity contingent upon observation of others' pain and touch may reflect the mapping of sensory qualities of observed painful and tactile stimuli. Results indicate that the S1 is not only involved in the actual perception of pain and touch but also plays an important role in extracting somatic features from social interactions.