Unmasking of presynaptic cutaneous HFOs burst by DBS lead recordings

We have carefully read the article: exploring the physiology and function of high-frequency oscillations (HFOs) from the somatosensory cortex, by Ozaki and Hashimoto (2011). Although we find this paper very interesting, we disagree with the method described to obtain HFOs due to pure cutaneous stimulation and we disagree with the conclusions on the consecutive presynaptic cortical burst reported as undetectable. In fact the index finger stimulation through a pair of ring electrodes attached at the proximal and distal interphalangeal joint elicited action potentials coming from both cutaneous and the Golgi tendon organs afferent fibers; accordingly, the HFOs are not of a pure cutaneous origin. In a previous report (Restuccia et al., 2002) we have described the detailed technique for selective electrical stimulation of muscle as well as cutaneous afferents able to evoke modality-specific responses in somatosensory evoked potentials (SEPs) recorded on the scalp of humans. To obtain pure cutaneous responses we have recorded SEPs after stimulation of the distal phalanx of the thumb, which selectively involve only cutaneous afferent. Our results are substantially in agreement with those of Ozaki and Hashimoto in which cutaneous inputs elicit larger cortical low frequency potentials compared to proprioceptive inputs (see Fig. 6 and Table 1 of Restuccia et al., 2002). Therefore we support the assertion that electrical median nerve stimulation at the wrist evokes sensory responses at the subcortical or primary somatosensory cortex that are attributed mainly to volleys of cutaneous afferents rather than those of muscle spindle afferents or tendon organ afferents.