Cortical integration of bilateral nociceptive signals: when more is less.

Integration of nociceptive information is essential to produce adapted responses, in order to promote body integrity and survival. However, how the brain integrates nociceptive inputs from different body areas remains unknown. The aim of the present study was to examine the cortical integration of bilateral nociceptive inputs evoked by laser heat stimuli. Sixteen healthy volunteers (8 F, 8 M; age: 25.5 ± 4.3) were recruited to participate in one session during which painful laser stimuli were applied to their hands with two Nd:YAP laser systems. Electroencephalographic activity was recorded to measure laser-evoked potentials and event-related spectral perturbations. Twenty nociceptive stimuli were applied in each of the four counterbalanced conditions: 1) right hand 2) left hand, and both hands with 3) attention to the right or 4) attention to the left. Compared with unilateral conditions, N2 and P2 peak amplitude as well as gamma oscillation power were decreased in bilateral conditions (p<0.05), but these effects were not affected by the direction of attention (p>0.1). In contrast, pain was not significantly different in any condition (p>0.05). These findings show that although more nociceptive inputs reach the brain with multiple nociceptive stimuli, their sensory representation is decreased while pain perception remains unchanged. These interactions between cerebral processing of nociceptive information from different body regions could support coordinated behavioral responses when pain origins from multiple sources.