Nicotine enhances auditory processing in healthy and normal-hearing young adult nonsmokers

Abstract

Rationale: Electrophysiological studies show that systemic nicotine narrows frequency receptive fields and increases gain in neural responses to characteristic frequency stimuli. We postulated that nicotine enhances related auditory processing in humans.

Objectives: The main hypothesis was that nicotine improves auditory performance. A secondary hypothesis was that the degree of nicotine-induced improvement depends on the individual's baseline performance.

Methods: Young (18-27 years old), normal-hearing nonsmokers received nicotine (Nicorette gum, 6mg) or placebo gum in a single-blind, randomized, crossover design. Subjects performed four experiments involving tone-in-noise detection, temporal gap detection, spectral ripple discrimination, and selective auditory attention before and after treatment. The perceptual differences between posttreatment nicotine and placebo conditions were measured and analyzed as a function of the pre-treatment baseline performance.

Results: Nicotine significantly improved performance in the more difficult tasks of tone-in-noise detection and selective attention (effect size = - 0.3) but had no effect on relatively easier tasks of temporal gap detection and spectral ripple discrimination. The two tasks showing significant nicotine effects further showed no baseline-dependent improvement.

Conclusions: Nicotine improves auditory performance in difficult listening situations. The present results support future investigation of nicotine effects in clinical populations with auditory processing deficits or reduced cholinergic activation.

Keywords: Acetylcholinergic systems; Auditory processing; Nicotine; Selective attention; Spectral ripple discrimination; Temporal gap detection; Tone in noise detection.

Figure 1.

Study design. In Session 1, subjects were first tested with audiogram, then completed pre-treatment testing in order of TIN (tone-in-noise detection), TGD (temporal gap detection), SMRT (spectral-temporally modulated ripples test), and TAIL (test of attention in listening). The subjects were then treated with either nicotine or placebo, and waited for 25 mins before the post-treatment testing in the same order. The four experiments usually took 0.5–1 h to complete. In Session 2, ≥48 h after Session 1 to allow for treatment clearance, the subjects completed the same tests, except for audiogram, in the same order as Session 1.

Figure 2.

Post-treatment placebo and nicotine difference as a function of pre-treatment baseline performance in four auditory experiments. a. Tone-in-noise detection. Individual data are represented by circles (red for 2000 Hz and blue for 4000 Hz). The mean difference is represented by the thick dashed horizontal line. The regression line is represented by the dotted line. The text box shows the linear regression equation (top), r² and p value (middle), and the mean difference, standard deviation, and the one-sample t-test result (bottom). The same convention is applicable to panel b, c, and d. b. Temporal gap detection. WC=Within-Channel, BC=Between-Channel. c. Spectral-Temporally modulated ripple discrimination. RPO=Ripples Per Octave. d. Selective attention.