The limbic system is the center of emotions and consists of structures located on top of the brainstem. Two significant system structures are the hippocampus and the amygdala. A major role of the hippocampus is in memory and CHRONIC STRESS damages the learning and memory abilities of humans and rodents.Why is this so? The damaging effects on learning and memory have been linked with structural changes in the neurons of the hippocampus. Chronic and sustained stress enhances secretion of the neuropeptide corticotropin-releasing hormone (CRH) from hippocampal interneurons which activate the receptors (CRF) found on the cell dendrites (Ivy, Rex, Chen, Dubé, Maras, Grigoriadis, Gall, Lynch & Baram, 2010). Constantly elevated interaction between the CRH and CRF is essentially the contributor to the structural and cognitive impairments as a result of early chronic stress. In other words, chronic stress is capable of shrinking areas of the brain, particularly the hippocampus (BrainSource, 2001). These are negative effects that stretch over from early life to even middle age and old age. Hence, it is not uncommon for people exposed to prolonged stress to report forgetfulness and learning difficulties.
Don’t forget the amygdala that is also a part of the forebrain! The amygdala is a structure that reacts very strongly to emotionally charged events, both positive and negative (Lurie, 2003). For example, we can remember what we were doing on September 11, 2001. That is the function of the hippocampus. However, we are able to remember the traumatic event because of the amygdala.
As mentioned, when faced with chronic stress, the hippocampus shrinks. The dendrites become fewer and branch out less, meaning there are fewer synaptic connections, and therefore these cells are not receiving as much information as they usually do.
It is the opposite in the case of the amygdala. With chronic stress, the neurons in the amygdala increase in size. Research done in depressive illness has shown that during the illness, the amygdala becomes larger and more active.
After exposure to chronic stress, the shrinking hippocampus and growing amygdala might result in us experiencing all sorts of anxieties, anger and fear remaining unconnected to where we were and what we were doing specifically. Generalised anxiety then arises (Lurie, 2003).
