A study of logon-evoked middle latency responses in female subjects with normal hearing

The middle latency response (MLR) to an acoustic stimulus occurs between 10 and 80 ms. The waveform is characterized by a series of peaks and troughs labeled N0, P0, Na, Pa, Nb and Pb. Certain acoustic stimuli may excite specific cochlear areas in contrast with clicks, that activate the cochlea between 1000 and 4000 Hz. The logon stimulus activates segmentar areas of the cochlea and has advantages over clicks when assessing low frequency areas of the cochlea (below 1 kHz). Aim: The aim of this paper was to study the MLR electrophysiologic response when activated by logon stimuli at 500, 1000 and 2000 Hz. Method- a prospective and descriptive study. 14 female volunteers had normal otology and conventional audiology results. The stimulus was monoaural and ipsilateral (Cz/A1-2). Results- the NaPa complex was readily identified compared to other complexes and was present in 100% of the tests done at 2000 Hz, and in 96.4% of the tests done at 500 and 1000 Hz. Conclusion-the logon stimulus at 500, 1000 and 2000 Hz elicits MLRs; the NaPa complex was the most frequent event and the 2000 Hz frequency elicited more responses than other frequencies.