Somatosensory evoked fast optical intensity changes detected non-invasively in the adult human head

This work is the first to report optical intensity changes (Delta I/I appro ximate to 0.05%) with a latency between 60 and 160ms after electrical media n nerve stimulation at 5 Hz detected non-invasively through the intact adul t human skull in volunteers. The signal is localised and reproducible when measuring at the same position on successive examinations. Compared to prev ious reports of fast optical changes in the human adult by a single group ( Psychophysiology, 32 (1995) 505) the here reported changes are much smaller . They are in line with results from a photon transport calculation on a he ad model employing data from exposed cortical tissue. The origin of the sig nal found here is still unclear, however, they might be the non-invasive eq uivalent to the scattering changes found in exposed cortical tissue studies (J. Neurophysiol., 78 (1997) 1707). (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.