The effect of multiple pulses of light on the circadian phase response of the rat

Multiple pulses of light administered to humans have been reported to resul t in type 0 phase responses. These results suggest the underlying pacemaker to be nonsimple. At present, results with this type of protocol have only been reported for humans. Therefore, multiple pulses of light were administ ered to rats. Rats were exposed to one, two, three, or four pulses of light for 5 h (1000 lux) at successive 24-h intervals. Results did not suggest a type 0 phase response. Nonetheless, results with a second, third, or fourt h light exposure were not fully predictable from a phase response curve der ived from a single light pulse.