The H-1-receptor antagonist dextro-chlorpheniramine impairs selective auditory attention in the absence of subjective awareness of this impairment

Although previous studies have shown that the human attention system is par tially affected by chlorpheniramine, the effects of chlorpheniramine on hum an auditory selective attention have not yet been explored. This study exam ines the effects of a single dose of 4 mg of dextro-chlorpheniramine on hum an auditory selective attention by means of the evaluation of the event-rel ated brain potential (ERP) processing negativity (PN). The study sample con sisted of 20 healthy male humans, who received either a single 4-mg dose of dextro-chlorpheniramine or a placebo in a double-blind design. The subject s were given a dichotic listening task, in which they were instructed to pr ess a response button upon detecting deviant tones (target) while their ERP s were recorded. In parallel, subjective tests evaluated the daytime sleepi ness, overall vigor, and affect of the subjects. Results showed that the au ditory selective attention is impaired under the effects of chlorpheniramin e, as reflected by an attenuation of PN amplitude and by a decrease of perf ormance in the group of subjects who took a single 4-mg dose of dextro-chlo rpheniramine. No subjective change in the daytime sleepiness, overall vigor , or affect of the subjects was observed. This lack of conscious awareness of the side effects may lead to situations of risk in tasks for which audit ory information is important, because no subjective indicators of attention impairment are available to the subjects.