Objective response detection in an electroencephalogram during somatosensory stimulation

Techniques for objective response detection aim to identify the presence of evoked potentials based purely on statistical principles. They have been s hown to be potentially more sensitive than the conventional approach of sub jective evaluation by experienced clinicians and could be of great clinical use. Three such techniques to detect changes in an electroencephalogram (E EG) synchronous with the stimuli, namely, magnitude-squared coherence (MSC) , the phase-synchrony measure (PSM) and the spectral F test (SFT) were appl ied to EEG signals of 12 normal subjects under conventional somatosensory p ulse stimulation to the tibial nerve. The SFT, which uses only the power sp ectrum, showed the poorest performance, while the PSM, based only on the ph ase spectrum, gave results almost as good as those of the MSG, which uses b oth phase and power spectra. With the latter two techniques, stimulus respo nses were evident in the frequency range of 20-80 Hz in all subjects after 200 stimuli (5 Hz stimulus frequency), whereas for visual recognition at le ast 500 stimuli are usually applied. Based on these results and on simulati ons, the phase-based techniques appear promising for the automated detectio n and monitoring of somatosensory evoked potentials. (C) 2000 Biomedical En gineering Society. [S0090-6964(00)00606-8].