Chronic stress can increase cortisol levels. The hippocapus is very rich in cortisol receptors so increased cortisol and disconnect existing neural networks, decrease capacity to learn, and contribute to memory loss. An exteme form of this type of memory loss can be seen in clinical conditions such as extreme depression and PTSD. (Goleman, Daniel Jay, PhD. The Brain and Emotional Intelligence: New Insights. p 46-50. MA: More Than Sound, 2011)