Auditory middle latency responses in chronic smokers compared to nonsmokers: differential effects of stimulus and age

Effects of clicks and tonebursts on early and late auditory middle latency response (AMLR) components were evaluated in young and older cigarette smokers and nonsmokers.

Participants ( n = 49) were categorized by smoking and age into 4 groups: (a) older smokers, (b) older nonsmokers, (c) young smokers, and (d) young nonsmokers. Monaural, 2-channel AMLRs were acquired from Fz and Cz electrodes with 3 stimuli (clicks, 500 Hz, and 3000 Hz).

Group differences included significantly higher V-Na amplitude in young adults and shorter Pb latency in older nonsmokers. Young smokers had a significantly higher Nb-Pb amplitude and shorter Nb latency than other groups. Toneburst stimuli yielded significantly longer V, Na, and Pa latencies compared to clicks. Pb latency was shorter at Fz than at Cz. Relative amplitudes were significantly higher at Fz than at Cz overall; Pa-Nb and Nb-Pb were significantly lower for 3000 Hz than for 500 Hz and clicks.

Responses from young smokers revealed a higher amplitude and shorter latency for later AMLR waves, reflecting an arousal effect of smoking in cortical and subcortical generators. AMLR differences in older adults may be due to age-related neurochemical changes in the central nervous system. Stimulus and electrode differences plus smoking and aging effects can guide neurodiagnostic AMLR protocols, especially in young adult smokers.