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Experiments Elucidate the Effects of Stress on Memory
> 3/14/2008 1:35:14 PM

Stress puts the body on alert so that it can prepare for danger. In the process of boosting some emergency systems, others are deprived of energy or even actively turned off. For example, when the fight-or-flight response is triggered, non-essential digestive systems are shut down. Two studies published this month suggest that memory formation is one of the systems that can be disrupted by stress.

Dr. Jill Mateo published an article in Neurobiology of Learning and Memory about her experiments with juvenile squirrels. She evaluated their ability to learn predator calls and spatial navigation. After observing normal abilities, she manipulated their levels of cortisol, a powerful stress hormone. Interestingly, learning was impaired at both high AND low levels of cortisol. This finding that moderate levels of stress are ideal for learning may be valuable for humans taking on new projects. Too much complacency and too much worry will make it much harder to master a situation.

Research by Dr. Tallie Baram, published last month in The Journal of Neuroscience, independent of the work of Mateo, helps to explain how stress chemically interferes with memory. However, instead of looking at cortisol, the usual suspect, Baram focused on corticotropin releasing hormones (CRH). She found that when CRH entered the hippocampus, dendritic spines crucial for learning rapidly degrade. To confirm the causality, she demonstrated that this dendritic damage could not occur in mice injected with CRH blockers.

It is clear from these two studies that stress hormones can impair learning when present in extreme quantities. This has both therapeutic and policy implications. Therapists should consider the learning problems that their PTSD or anxiety disorder patients may be suffering, and researchers should explore ways to protect the brain from excessive stress hormones. CRH blockers look like a good place to start. The policy implications should be pondered by organizations that send their members into stressful environments while expecting them to quickly assess the situation (i.e. the military, U.N. observers, etc). In addition, juries may want to consider the fact that witness memory formation can be impaired by traumatic events, perhaps making the panicked victim of a crime less likely to remember the details than a distant observer peering from their window.

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