Short latency somatosensory evoked potentials in brain-dead patients using restricted low cut filter setting

This paper describes the SSEP patterns in BD when using restricted filter bandpass setting, with special emphasis on the dissociation of some SSEP components when cephalic and non-cephalic references are used. A characteristic SSEP pattern was found: absence of N20 and later responses in the Cc'-Fpz lead and preservation of all or some of the so-called subcortical components in the rest of the derivations. We noted an interesting dissociation in which some SSEP components were not recorded in the scalp-non cephalic derivations, but they were still present in the neck-cephalic and spine channels, with inverse polarity. We selected a restricted bandpass for the scalp-non cephalic, the neck-cephalic and the spine derivations, and we found this dissociation not only for P13-N13 and P14-N14, but for Nm-Pm' and Pm-Nm' components. It is likely that components Nm-Pm' and Pm-Nm' are "far-field potentials" that appear when the slow wave N18 is filtered out by the use of a restricted low filter setting. Our data further suggest that all components after N14-P14, recorded with restricted filter bandpass also recognize two distinct generator sources. Rostral generators are located probably in the brainstem and/or thalamus, but at least a significant part of these SSEP components are generated at the very lower part of the medulla oblongata (dorsal column nuclei) and/or at the upper cervical spine.(ABSTRACT TRUNCATED AT 250 WORDS)