The article by Galambos et al. describes the 40-Hz auditory potential, a sequence of brain potentials that appear 5 to 80 msec after sound stimuli and resemble 3 to 4 cycles of a 40-Hz sine wave. When these stimuli are repeated at a rate of about 40 per second, the individual waves combine to form a single, stable composite wave, known as the 40-Hz event-related potential (ERP). This phenomenon has several interesting properties: 1. **Sensory Processing**: The 40-Hz ERP disappears with surgical anesthesia and shows similarities to similar phenomena in the visual and olfactory systems, suggesting that adequate sensory information processing may require cyclical brain events in the 30- to 50-Hz range. 2. **Information Content**: The latency and amplitude measurements of the 40-Hz ERP may provide useful information about the number and basilar membrane location of the auditory nerve fibers excited by a given tone. 3. **Clinical Applications**: The response is present at sound intensities very close to normal adult thresholds for audiometric frequencies, which could have applications in clinical hearing testing. The authors detail the methods used to extract and analyze the 40-Hz ERP, including the use of various signal generators, earphones, and averaging computers. They report that the 40-Hz ERP is closely related to the middle-latency response (MLR) and can be extracted from the electroencephalogram (EEG) recorded between electrodes at the forehead and earlobe. The response consists of a series of forehead-negative (N) and positive (P) waves with a time interval of about 25 msec between successive waves. The article also discusses the effects of stimulus rate, intensity, and frequency on the 40-Hz ERP. The response amplitude decreases as the frequency of the stimulus increases, and the response latency shortens. These effects are consistent across different subjects and suggest that the 40-Hz ERP may reflect the activation of specific auditory nerve fibers and the mechanical wave propagation along the basilar membrane. Finally, the authors compare the 40-Hz ERP to other sensory modalities, such as vision and olfaction, and discuss the potential for further research to identify the anatomical structures and physiological processes that generate these responses. They suggest that the 40-Hz ERP could be a practical tool for examining the distant basilar membrane events through large electrodes placed on the human scalp.The article by Galambos et al. describes the 40-Hz auditory potential, a sequence of brain potentials that appear 5 to 80 msec after sound stimuli and resemble 3 to 4 cycles of a 40-Hz sine wave. When these stimuli are repeated at a rate of about 40 per second, the individual waves combine to form a single, stable composite wave, known as the 40-Hz event-related potential (ERP). This phenomenon has several interesting properties: 1. **Sensory Processing**: The 40-Hz ERP disappears with surgical anesthesia and shows similarities to similar phenomena in the visual and olfactory systems, suggesting that adequate sensory information processing may require cyclical brain events in the 30- to 50-Hz range. 2. **Information Content**: The latency and amplitude measurements of the 40-Hz ERP may provide useful information about the number and basilar membrane location of the auditory nerve fibers excited by a given tone. 3. **Clinical Applications**: The response is present at sound intensities very close to normal adult thresholds for audiometric frequencies, which could have applications in clinical hearing testing. The authors detail the methods used to extract and analyze the 40-Hz ERP, including the use of various signal generators, earphones, and averaging computers. They report that the 40-Hz ERP is closely related to the middle-latency response (MLR) and can be extracted from the electroencephalogram (EEG) recorded between electrodes at the forehead and earlobe. The response consists of a series of forehead-negative (N) and positive (P) waves with a time interval of about 25 msec between successive waves. The article also discusses the effects of stimulus rate, intensity, and frequency on the 40-Hz ERP. The response amplitude decreases as the frequency of the stimulus increases, and the response latency shortens. These effects are consistent across different subjects and suggest that the 40-Hz ERP may reflect the activation of specific auditory nerve fibers and the mechanical wave propagation along the basilar membrane. Finally, the authors compare the 40-Hz ERP to other sensory modalities, such as vision and olfaction, and discuss the potential for further research to identify the anatomical structures and physiological processes that generate these responses. They suggest that the 40-Hz ERP could be a practical tool for examining the distant basilar membrane events through large electrodes placed on the human scalp.