ABSTRACT
Innervation of the cochlea by sympathetic fibers suggests that the autonomic nervous system (ANS) may influence auditory information processing. The brainstem frequency-following response (FFR) and spontaneous skin conductance activity (SCA) were measured while subjects discriminated between long (rare) and short (frequent) duration tones. When subjects were divided into three groups on the basis of SCA, those with low SCA variability had larger FFR amplitudes. These results agree with the only other study to report ANS effects on brainstem auditory evoked responses [28]. It is proposed that individual differences in autonomic response patterns may account for some of the amplitude variation reported in brainstem evoked potential studies.
Subject(s)
Autonomic Pathways/physiology , Brain Stem/physiology , Evoked Potentials, Auditory, Brain Stem/physiology , Acoustic Stimulation , Adolescent , Adult , Galvanic Skin Response/physiology , Humans , Reaction Time/physiologyABSTRACT
Simple motor reaction times (RT) in humans show marked trial-to-trial variations. In the present study, a brief tone (400 Hz, 37.5 ms duration) that was the imperative stimulus in a RT paradigm evoked the brainstem frequency-following response (FFR). Horizontal and vertical montage FFRs were recorded to evaluate neural responses with putative origins in auditory nerve and central brainstem, respectively. The main question concerned the possible relationship between trial-to-trial variations in RT speed and FFR response properties. The results showed a reliable pattern in which fast RT trials yielded larger amplitudes (relative to slow trials) in earlier milliseconds of the FFR, and slow RT trials yielded relatively larger amplitudes in later milliseconds of the response. These results support the conclusion that early processing in the auditory brainstem is not automatic and invariant. Rather, short-latency evoked potentials appear to reflect trial-to-trial variations related to events far removed from the first synapse of sensory coding, perhaps depending upon cortically mediated influences such as cognition or attention.
