Fig. 4. Effect of physostigmine on the propofol-induced reduction of the auditory steady state response (ASSR) during loss of consciousness. (A ) ASSR amplitudes of individual subjects are shown. Filled circles denote patients in whom loss of consciousness was reversed by the physostigmine (n = 9). Diamonds indicate patients in whom unconsciousness was not reversed (n = 2). One of these two patients remained clearly unconscious after physostigmine administration (subject 1), whereas the other showed an equivocal level of consciousness (subject 2). (B ) The ASSR amplitude (mean ± SD, n = 9) during baseline, propofol-induced unconsciousness, physostigmine-induced reversal of the unconsciousness, and recovery. ASSR amplitude was significantly reduced when subjects were unconscious compared with the baseline, after physostigmine administration, and during recovery (*P < 0.05, 0.01, and 0.001, respectively). After administration of physostigmine, amplitude returned toward baseline values. Numbers above each histogram plot indicate ± (SD).