Figure 1.

The effects of controllable versus uncontrollable stress on “learning” depend on what the animal can learn. (A) Adult male rats were trained each day for seven days (d1–d7) on an operant conditioning task in which they could learn to escape from a mild footshock. The graph to the left shows response times (mean latency in seconds ± SEM) for rats that could escape. These rats were yoked to animals that could not escape but were nonetheless exposed to the same amounts of shocks. One day after this manipulation, all animals were trained on a similar task except that they had to cross the shuttle box twice in order to terminate the shocks. The new task was also conducted in a new context. As shown, those that were exposed to the inescapable stress in the first phase did not learn to escape in the second phase of training, whereas those that were exposed to the escapable stress rapidly learned to escape (Shors et al. 2005). Rats that were not pretrained on the escape task (No Stress) performed moderately well, but not as well as those that learned to escape. Asterisk denotes a significant change in response relative to the response from the No Stress group. (B) As represented in Figure 1A, adult male rats were trained each day for seven days (d1–d7) on an operant conditioning task in which they could learn to escape from a mild footshock. The graph on the left shows response times (mean latency in seconds ± SEM) for rats that could escape. These rats were yoked to animals that could not escape but were nonetheless exposed to the same amounts of shocks. One day after this manipulation, all animals were trained with a classical eyeblink conditioning task using a trace paradigm in which the conditioned stimulus and the unconditioned stimulus are separated slightly in time (500 ms). The graph on the right shows the percentage of conditioned responses in all groups, including a group of animals that were not exposed to the escape training. Only the animals exposed to the uncontrollable stress responded differently, and they responded with a greater percentage of conditioned responses (Leuner et al. 2004b). Asterisk denotes a significant change in response relative to the response from the No Stress group.