Increasing the efficiency of neonatal MEG measurements by alternating auditory and tactile stimulation.

OBJECTIVE: To evaluate the possible effect of intervening auditory stimulation on somatosensory evoked magnetic fields in newborns. METHODS: We recorded auditory and tactile evoked responses with magnetoencephalography (MEG) from two groups of healthy newborns. One group (n=11) received only tactile stimuli to the index finger, the other (n=11) received alternating tactile and auditory (vowel [a:] with 300-ms duration) stimuli. The interval between subsequent tactile stimuli was always 2 s. We analyzed the equivalent current dipoles (ECDs) of the main auditory and somatosensory responses. RESULTS: The ECDs of the tactile responses agreed with activation of the primary somatosensory cortex at ∼60 ms and the secondary somatosensory region at ∼200 ms. The source of the auditory response (∼250 ms) was clearly distinct from those to tactile stimulation and in line with auditory cortex activation. The intervening auditory stimulation did not affect the strength, latency, or location of the ECDs of the tactile responses. CONCLUSIONS: Auditory and tactile MEG responses from newborns can be obtained in one measurement session. SIGNIFICANCE: The alternating stimulation can be used to shorten the total measurement time and/or to improve the signal to noise ratio by collecting more data.