Somatosensory evoked magnetic fields from the primary and secondary somatosensory cortices in healthy newborns.

Although brain development has been actively investigated in animals, maturation of the cerebral cortex in human newborns is still poorly understood. This study aimed at characterizing the cortical areas participating in tactile processing in human neonates. Somatosensory-evoked magnetic fields were recorded from 21 healthy full-term newborns during natural sleep. Altogether, four cortical areas were activated by tactile stimulation: the contra- and ipsilateral primary (SI) and secondary (SII) somatosensory cortices. The contralateral SI was activated first in all the newborns. This early activity was not affected by the interstimulus interval or the sleep stage. The contralateral SII activation at around 200 ms was prominent in quiet sleep (QS) but attenuated in active sleep (AS). Activity in this area was strongly depressed by a faster rate of stimulation. Ipsilateral activity was seen in most subjects: more often in QS than AS. The ipsilateral activity originated from SII in most babies, but in some the ipsilateral SI was also activated. We conclude that both the contra- and ipsilateral SI and SII can participate in the processing of somatosensory information in human neonates.