EFFECT OF ACOUSTIC STIMULUS CHARACTERISTICS ON THE STARTLE RESPONSE IN HOODED RATS

The acoustic startle response (ASR) depends on stimulus parameters suc h as duration, intensity and particularly on the stimulus rise time. T he aim of our study was to determine to what extent the ASR parameters are affected by the spectral characteristics of the stimulus. Therefo re, in this experiment the amplitude and the latency of the acoustic s tartle reflex were assessed for a fixed pulse duration and for a varie ty of stimulus frequencies ranging between 3 and 23 kHz. The ASRs were studied in 11 adult hooded rats exposed to 2-ms (120 dB SPL) tone pul ses of different frequencies presented in random order, with or withou t 70 dB white noise background. Statistical analysis of the data revea led significant differences between ASR amplitudes for different frequ encies. In our experimental situation the rats responded more readily to a low frequency stimulus. The startle amplitude decreased with tona l frequencies and distinguishable difference were seen for 3, 7, and 1 0 kHz pulses. However, such differences were not readily observed for higher frequencies i.e. 15, 20, 23 kHz. The same pattern of difference s was observed when the acoustic stimulus was presented with the white noise background. The observed differences may be attributed, firstly , to a spectral characteristic of the stimulus and thus to an audibili ty in rats and secondly to a behavioral meaning of a stimulus of a dif ferent frequency.