Electroencephalographic nogo potentials in a no-movement context: the case of motor imagery in humans.

The nogo potentials (N2/P3) were studied in a precuing auditory reaction time task in human subjects who had to either perform a button-press response (Press condition) or imagine they were performing it (Imagine condition). In the full precue condition (the subjects knew in advance which response they had to perform/imagine), in 25% of the trials, a nogo signal instructed the subject not to perform or not to imagine the prepared action. Clear N2/P3 components were obtained on nogo trials on the Press trials, but also on the Imagine ones: the N2 was of similar amplitude in both conditions, whereas the P3 was of smaller amplitude in the Imagine condition. The presence of nogo potential in motor imagery is discussed in terms of the functional significance of the N2/P3 complex.