A 40-Hz auditory potential recorded from the human scalp.

TLDR

The 40‑Hz event‑related potential (ERP) is a brainwave pattern that appears 8–80 ms after sound, disappears under anesthesia, and is thought to reflect essential cyclical processing of sensory information in the 30–50 Hz range. When sounds are presented at ~40 Hz, the ERP’s 3–4 cycles combine into a stable composite wave, and its latency and amplitude can reveal the number and basilar‑membrane location of excited auditory‑nerve fibers, even at near‑threshold intensities, suggesting clinical hearing‑testing applications.

Abstract

Computer techniques readily extract from the brainwaves an orderly sequence of brain potentials locked in time to sound stimuli. The potentials that appear 8 to 80 msec after the stimulus resemble 3 or 4 cycles of a 40-Hz sine wave; we show here that these waves combined to form a single, stable, composite wave when the sounds are repeated at rates around 40 per sec. This phenomenon, the 40-Hz event-related potential (ERP), displays several properties of theoretical and practical interest. First, it reportedly disappears with surgical anesthesia, and it resembles similar phenomena in the visual and olfactory system, facts which suggest that adequate processing of sensory information may require cyclical brain events in the 30- to 50-Hz range. Second, latency and amplitude measurements on the 40-Hz ERP indicate it may contain useful information on the number and basilar membrane location of the auditory nerve fibers a given tone excites. Third, the response is present at sound intensities very close to normal adult thresholds for the audiometric frequencies, a fact that could have application in clinical hearing testing.