Monday, October 01, 2007

Learning in stressful times

The hippocampus is crucial for mediating the effects of stress on learning, even when this brain region is not directly involved in learning the task in question, reports a paper in the November issue of Nature Neuroscience.

The hippocampus is important for some types of learning but not others. Eyeblink conditioning, for example, does not require the hippocampus. Animals respond to a shock to the eye by blinking, and when the shock is repeatedly paired with a noise learn to respond to the noise itself with an eyeblink – irrespective of whether it is accompanied by a shock.

Tracey Shors and colleagues previously reported that after rats have been stressed, eyeblink conditioning is enhanced in males and reduced in females – stress therefore modifies learning of the association between the noise and shock. The authors now find that selective damage to the hippocampus in rats makes these stress-induced modifications disappear. Lesioned male rats do not learn eyeblink conditioning any faster when they are stressed, and lesioned female rats are no worse. Without stress, both perform just like normal animals. These results indicate that neuronal activity in the hippocampus modifies learning after stress, even when the hippocampus is not directly involved in the learning process itself.
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