Dipole-tracing of 'awareness' attenuating the cortical components of somatosensory evoked potentials

Using the dipole-tracing method, the source generators of N₁₈, P₂₂ and P₄₀ of the somatosensory evoked potential (SEP) were estimated as the equivalent dipole. After voluntary action of the thumb flexion, no changes were observed in N₁₈ or P₄₀, but the amplitude of P₂₂ was suppressed. The after-effects of intention accompanied by a voluntary action or the subject's awareness that electrical stimulation will be given after the voluntary action were treated as 'awareness'. By subtracting the pure SEP from SEP during 'awareness', it was found that the equivalent dipole of 'awareness' of P₂₂ was located at the same region of pure P₂₂, but the vector was of opposite orientation. 'Awareness' attenuated the perceptive potential of SEP like P₂₂ generated in the cortex.