Single-trial detection of human brain responses evoked by laser activation of Adelta-nociceptors using the wavelet transform of EEG epochs.

The aim of this study was to identify EEG changes induced by Adelta-nociceptor activation in single trials. In a preliminary experiment, intense CO(2) laser stimuli were delivered to the hand dorsum of five volunteers. The average amplitude of EEG epochs was estimated in the time-frequency (TF) domain using the continuous Morlet wavelet transform (CMT). The result was used as a TF filter enhancing Adelta-nociceptor induced EEG responses. In a second experiment, eight other subjects were delivered laser stimuli with six intensities. The CMT of each EEG epoch was computed. After applying the TF filter, amplitudes within a predefined interval were summed. Whether this sum predicted the occurrence of Adelta-nociceptor activation was tested using the reaction-time to discriminate between Adelta- or C-fibre mediated detection. Results showed that this method accurately identified single-trial EEG responses to Adelta-nociceptor activation.