Modification of acoustic and tactile startle by single microwave pulses

Single microwave pulses at 1.25 GHz were delivered to the head and neck of male Long-Evans rats as a prestimulus to acoustic and tactile startle. For acoustic startle, pulses averaging 0.96 μs in duration were tested with two specific absorption rate (specific absorption) ranges, 15.0–30.0 kW/kg (16.0–44.2 mJ/kg) and 35.5–86.0 kW/kg (66.6–141.8 mJ/kg), delivered 201, 101, 51, 3, and 1 ms before and 1 ms after onset of a startling noise. The low-intensity pulse did not affect peak amplitude, integral, or latency of the whole-body startle response. The high-intensity pulse at 101 and 51 ms inhibited the startle response by decreasing peak amplitude and integral; at 201 and 51 ms latency was increased. The high-intensity pulse at 1 ms enhanced the startle response by increasing peak amplitude and at 3 ms by increasing integral. For tactile startle, either microwave pulses averaging 7.82 μs in duration and 55.9–113.3 kW/kg (525.0–1055.7 mJ/kg) or 94 dB SPL clicks were delivered 157, 107, 57, and 7 ms before and 43 ms after onset of a startling air burst. The microwave pulse at 57 ms inhibited the startle response by decreasing peak amplitude; at 157, 107, 57, and 7 ms it increased latency. The microwave pulse at 43 ms after onset enhanced the startle response by increasing peak amplitude. The acoustic click at 157 and 57 ms inhibited the startle response by decreasing peak amplitude; at 157, 107, and 57 ms it increased latency. The microwave pulse inhibition and enhancement of startle were similar to previously reported effects of sensory stimuli delivered at similar lead times, indicating the possibility that action was mediated by sensory stimulation.