Conditioned brain-stimulation reward attenuates the acoustic startle reflex in rats

The acoustic startle reflex (ASR) in rats is attenuated by a light paired w ith food or, in humans, by "pleasant" pictures. Rats were trained to barpre ss for lateral hypothalamus (LH) stimulation. ASR amplitudes were then meas ured at 4 intensities, with or without a light. Control rats that did not r eceive brain-stimulation reward (BSR) showed initially lower ASR amplitudes than did rats exposed to BSR, but both groups responded similarly with or without light. Next, experimental rats were given BSR in the presence of li ght but not in its absence. After conditioning, ASR amplitudes were reduced , and ASR thresholds were raised by a mean of 2.6 dB in the light but remai ned at preconditioning levels without light. No such change was found for c ontrol rats or rats with placements outside the LH.