40-Hz auditory event-related potential in normal adults

Normative data for 40-Hz event-related potentials to 500-Hz tonal stimuli in young and elderly subjects

Recordings of 40-Hz event-related potentials (ERPs) were obtained in 81 young subjects (18-40 years) and in 20 elderly subjects (60-77 years) with hearing normal for their age. The stimuli were 500-Hz logons. The first negative peak (N1) of the response was analyzed. With increasing intensity the amplitude of the responses increased and the latency decreased for all subjects. The 40-Hz ERP was obtained within 10 dB of the behavioral threshold for more than 80% of the population under study. The N1 was prolonged in latency and enhanced in amplitude in the older subjects. No differences were found between young and elderly subjects regarding binaural interaction, or in responses elicited by ipsi- and contralateral stimulation. From the clinical point of view, the 40-Hz ERP recordings of young and elderly subjects are similar.

40-Hz steady-state responses in newborns and in children

The authors investigated the 40-Hz steady-state responses (SSR) in 32 full-term newborns and in 10 normal children (5-8 years old), using 500-Hz tone bursts. The 40-Hz SSR threshold is located at about 50 and 30 dB nHL in newborns and older children, respectively. The latencies of both P1 and N1 waves decreased significantly with age, while the amplitudes increased. No significant latency and amplitude intersex differences have been observed. Moreover, with age, the 40-Hz SSR became more stable, their test-retest replicability improved, and P1-N1 wave occurrence increased. The authors finally discuss the possible underlying mechanisms of these findings and conclude that the 40-Hz SSR are difficult to obtain and are scarcely reliable in defining the low-frequency threshold in newborns. The stability and reliability of the responses increase with age, and the electrophysiological and behavioral thresholds to low-frequency stimuli tend to overlap.