Abstract
Watching another person’s hand movement modulates somatosensory evoked magnetic fields (SEFs). Assuming that the mirror neuron system may have a role in this phenomenon, oxytocin should enhance these effects. This single-blinded, placebo-controlled, crossover study therefore used magnetoencephalography (MEG) to investigate SEFs following electrical stimulation of the right median nerve in 20 healthy male participants during hand movement observation, which were initially presented as static images followed by moving images. The participants were randomly assigned to receive either oxytocin or saline during the first trial, with the treatment being reversed during a second trial. Log-transformed ratios of the N20 and N30 amplitudes were calculated and compared between moving and static images observations. Phase locking (calculated using intertrial phase coherence) of brain oscillations was also analyzed to evaluate alpha, beta and gamma rhythm changes after oxytocin administration. Log N30 ratios showed no significant changes after placebo administration but showed a decreasing tendency (albeit not significant) after placebo administration, which may suggest mirror neuron system involvement. In contrast, log N20 ratios were increased after placebo administration, but showed no significant change after oxytocin administration. Interestingly, the gamma band activity around N20 increased after placebo administration, suggesting that oxytocin exerted an analgesic effect on median nerve stimulation, and inhibited the gamma band increase. Oxytocin might therefore modulate not only the mirror neuron system, but also the sensory processing associated with median nerve stimulation.
Highlights
Somatosensory inputs from the periphery reach the contralateral primary somatosensory cortex (SI), which subsequently activates the ipsilateral SI and bilateral secondary somatosensory cortex (SII) [1,2]
A recent study with a sequential EEG-functional magnetic resonance imaging design showed similar patterns of mirror neuron activity and mu suppression; mu suppression was not confined to the mirror neuron areas, but involved a range of subcortical areas related to motor preparation and visual sensitivity [10]
All detected N20 equivalent current dipole (ECD) were localized in the primary somatosensory cortex, while all N30 ECDs were localized in the frontal cortex (Fig 2)
Summary
Somatosensory inputs from the periphery reach the contralateral primary somatosensory cortex (SI), which subsequently activates the ipsilateral SI and bilateral secondary somatosensory cortex (SII) [1,2]. The increase in the amplitude of N30, which was localized to the anterior wall of the central sulcus [6], was thought to have been associated with mirror neurons [5,7]. Studies have suggested that the mirror neuron system plays an important role in recognizing actions and understanding their meaning [8]. This system, which is active when either observing or executing the same action is thought to be closely connected to the electrophysiological mu suppression signal [9]. A recent study with a sequential EEG-functional magnetic resonance imaging (fMRI) design showed similar patterns of mirror neuron activity and mu suppression; mu suppression was not confined to the mirror neuron areas, but involved a range of subcortical areas related to motor preparation and visual sensitivity [10]
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