Phase locking between human primary and secondary somatosensory cortices

Area of Science:

• Neuroscience
• Somatosensory System Research
• Brain Connectivity Studies

Background:

• Unilateral peripheral nerve stimulation activates the primary somatosensory cortex (SI) contralaterally and the secondary somatosensory cortex (SII) bilaterally.
• Phase locking between brain regions is hypothesized to indicate coordinated processing or information exchange.

Purpose of the Study:

• To characterize the phase locking between SI and SII in response to electrical stimuli of the median nerve.
• To investigate the nature of sensorimotor system interactions during peripheral nerve stimulation.

Main Methods:

• Ongoing neuromagnetic activity was recorded from healthy volunteers using 204 planar gradiometers.
• Phase locking analysis was performed on single-trial data between sensors maximally sensitive to left SI and all other sensors.
• Stimuli were applied to the right median nerve every 3 seconds.

Main Results:

• Statistically significant phase locking was observed at approximately 20 Hz, 80-90 ms post-stimulus, between the left SI and right SII in 9 out of 10 subjects.
• Phase-locked activity was spatially distinct, with intervening sensors showing no locked activity, ruling out common source artifacts.
• A significant portion of the observed SI-SII phase locking was not time-locked to the stimuli, suggesting it may not be evident in standard evoked responses.

Conclusions:

• A unique, stimulus-induced phase-locked interaction exists between the left SI and right SII.
• This interaction likely reflects a specific form of information exchange or coordinated processing within the sensorimotor network.
• The findings provide novel insights into the dynamic connectivity of the human somatosensory system.