Stress, path integration, and the entorhinal cortex.

The stress induced release of glucocorticoids influences neural excitability and plasticity in the hippocampus. Surprisingly the entorhinal cortex (EC), an adjacent region, has received little attention in stress research, even though it is also rich in glucocorticoid receptors. Grid cells in the medial EC play a decisive role in path integration (PI). Interestingly, the EC is a brain region damaged very early in Alzheimer's disease (AD). Three recent studies investigated the associations between stress, cortisol and PI. In the first study chronic stress was associated with poorer PI. Acute stress induction impaired PI in the second study. In the third study cortisol administration impaired PI and reduced grid like representations in the EC as measured via fMRI. These findings have important implications. Future research on stress and spatial navigation should take the EC into account. Moreover, chronic stress is associated with an increased risk for AD. The findings suggest that the direct effect of cortisol on the EC may partially underly these clinical findings. Directions for future research are discussed.