Phasic Modulation of Human Somatosensory Perception by Transcranially Applied Oscillating Currents

Area of Science:

• Neuroscience
• Cognitive Science
• Perception

Background:

• Spontaneous brain network dynamics influence the perception of near-threshold sensory stimuli.
• Alpha oscillations in the brain, particularly in the visual cortex, have been shown to predict stimulus processing.
• The concept of 'pulsed inhibition' suggests a mechanism for sensory gating based on brain states.

Purpose of the Study:

• To investigate if 'pulsed inhibition' is a general mechanism for conscious perception across sensory modalities.
• To determine if non-invasive brain stimulation can modulate this sensory gating mechanism.
• To explore the effect of entraining somatosensory mu-alpha oscillations on tactile perception.

Main Methods:

• Healthy participants received transcranial alternating current stimulation (tACS) at their individual mu-alpha frequency over the somatosensory cortex.
• A sham stimulation condition was used as a control.
• Participants performed a detection task involving near-threshold somatosensory stimuli.

Main Results:

• While mean perception thresholds did not change, somatosensory detection thresholds varied significantly based on the phase of the applied tACS.
• This phase-dependent modulation was specific to somatosensory cortex stimulation at the mu-alpha frequency.
• No such effect was observed when tACS was applied over the visual cortex at the individual visual alpha frequency.

Conclusions:

• Transcranial alternating current stimulation (tACS) at an endogenous frequency can modulate somatosensory perception.
• This modulation occurs through phase-dependent entrainment of ongoing mu-alpha oscillations, inducing periods of excitation and inhibition.
• These findings support the 'pulsed inhibition' framework as a general, sensory-specific mechanism for conscious perception.