Modulation of pain perception through transcranial alternating current stimulation and its nonlinear relationship with the simulated electric field magnitude.

BACKGROUND: Oscillatory activities observed in multiple regions are closely associated with the experience of pain. Specifically, oscillatory activities within the theta- and beta-frequency bands, observed in the left dorsolateral prefrontal cortex (DLPFC), have been implicated in pain perception among healthy individuals and those with chronic pain. However, their physiological significance remains unclear. METHODS: We explored the modulation of pain perception in healthy individuals by theta- and beta-band transcranial alternating current stimulation (tACS) over the left DLPFC and examined the relationship between the modulation effect and magnitude of the electric field elicited by tACS in the left DLPFC using computational simulation. RESULTS: Our findings revealed that both theta- and beta-tACS increased the heat pain threshold during and after stimulation. Notably, the simulated electric field magnitude in the left DLPFC exhibited an inverted U-shaped relationship with the pain modulation effect for theta-tACS. CONCLUSIONS: Our study findings suggested that there would be an optimal electric field strength to produce a high analgesic effect for theta-tACS. SIGNIFICANCE: The application of theta- and beta-tACS interventions targeting the left DLPFC might facilitate the treatment of chronic pain. Furthermore, the attainment of effective pain modulation via theta-tACS over the DLPFC warrants the use of optimal stimulus intensity.

Effects of prior sustained tactile stimulation on the somatosensory response to the sudden change of intensity in humans: an magnetoencephalography study.

The rapid detection of sensory changes is important to survival. The change-detection system should relate closely to memory since it requires the brain to separate a new stimulus from past sensory status. To clarify effects of past sensory status on processing in the human somatosensory cortex, brain responses to an abrupt change of intensity in a train of electrical pulses applied to the hand were recorded by magnetoencephalography (MEG). In Experiment 1, effects of the magnitude of deviance (1.0, 0.5, 0.3, 0.2, and 0.1 mA) between conditioning and test stimuli were examined. In Experiment 2, effects of the duration of the conditioning stimulus (3, 1.5, 1.0, and 0.5 s) were examined. The abrupt change in stimulus intensity activated the contralateral primary (cSI) and secondary somatosensory cortex (cSII). The amplitude of the cSI and cSII activity was dependent on not only the magnitude of the change in intensity but also the length of the conditioning stimulus prior to the change, suggesting that storage of prior tactile information was involved in generating these responses. The possibility that an activity of onset (with no conditioning stimulus) would be involved in the change-related activity was also discussed.