Attention to painful stimulation enhances γ-band activity and synchronization in human sensorimotor cortex

A number of cortical regions are involved in processing pain-related information. The SI and SII somatosensory cortices process mainly sensory discriminative attributes but also play an important role in recognition and memory of painful events. Regions such as SII and the posterior insula appear to be the first stations that house processes by which attention profoundly shapes both behavioral responses and subjective pain experience. We investigated the influence of directed attention on pain-induced oscillations and synchronization processes using magnetoencephalogram in combination with an oddball paradigm in 20 healthy subjects. The subject's task was to count rare painful electrical stimuli applied to one finger, while ignoring frequent stimuli at a different finger. A high detection ratio was observed for all blocks and subjects. Early evoked oscillations in the delta-band increased with higher stimulus intensity and directed attention, most prominently at contralateral sensorimotor sites. Furthermore, suppression and rebound of beta activity were observed after painful stimulation. Moreover, induced oscillatory activity in the high gamma-band increased with directed attention, an effect being significantly stronger for high compared with low stimulus intensity. Coupling analysis performed for this high gamma response revealed stronger functional interactions between ipsilateral and contralateral sites during attention. We conclude that pain-induced high-frequency activity in sensorimotor areas may reflect an attentional augmentation of processing, leading to enhanced saliency of pain-related signals and thus to more efficient processing of this information by downstream cortical centers.