Figure 2.

Fear memory in rats trained with a 60 min or 24 h intertrial interval is long lasting. A, Rats were trained with a 4 min (n = 9), 60 min (n = 8) or 24 h (n = 8) training interval and tested 14 d after the second training trial. B, Rats with a 60 min or 24 h intertrial interval showed robust retention. C, Another group of rats (n = 8) trained with a 60 min intertrial interval and tested 30 d later showed very robust fear memory. D, Rats were given a single pairing of light and shock followed by a pairing of odor with shock. Rats were tested 2 d later in the presence of the light, odor, or light and odor in compound. E, There was no evidence of summation between the light and odor, as the rats showed negligible amounts of fear when the cues were presented in compound (*p < 0.05 vs 4 min).