Reflex modification as a test for sensory function.

Reflex modification is a versatile procedure for the assessment of sensory function because it can provide information about the responses of several sensory systems to both weak and intense stimuli. The procedure has two elements: The elicitation of some reflex, such as the acoustic startle reflex, and the modification of that reflex by preliminary stimuli. In these experiments we used reflex modification and reflex elicitation procedures to examine the normal development of auditory function in rats and to evaluate alterations in auditory function produced by physical and toxic insult. Adult rats exposed to octave bands of noise demonstrated frequency-specific deficits on a test of reflex modification, but not reflex elicitation. In the studies of developing rats, reflex elicitation appeared by postnatal day 12 and modification around day 14. Frequency-specific increases in both measures suggested that the phenomena were sensitive to auditory development and, not simply, motor development. Exposure to kanamycin on postnatal days 8 to 16 produced dose-related deficits in the ability to detect stimuli at 32 and 16 kHz, but not 4 and 0.8 kHz. These effects were observed in the absence of changes in reflex elicitation. The results demonstrate that reflex modification procedures provide more sensitive and specific information than that provided by the use of reflex elicitation alone.