Slow cortical potential shifts modulate the sensory threshold in human visual system

The relationship between the spontaneous slow cortical potential shifts and the detection of visual stimuli at sensory threshold were investigated. Th e mean slow cortical potentials preceding the detected stimuli were more ne gative than those preceding the missed stimuli. Accordingly, the stimulus d etection performance was higher during negative compared to positive cortic al potential shifts. These findings demonstrate that the cortical negativit y reflects increased excitability of neural networks, thereby facilitates t he detection of threshold stimuli, in contrast to cortical positivity. Ther efore, at near-threshold stimulus intensities one reason for detecting the stimulus in one trial but missing it in another could be the change in the EEG baseline between the trials. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.