The Role of Memory in the Onset of Depression

Depression is a mental illness characterised by extreme sadness and usually people suffering with it are full of guilt but cannot always state why they feel that way. Depression has become a fairly common mental illness as Kessler et al (1994b) found that around 17% of people will experience a major episode of depression during their life. Due to the growing numbers of people suffering and potentially going to suffer from depression, it is important to understand the causes of depression. Memory has been identified as having a role in the onset and course of depression, specifically autobiographical memory. Autobiographical memory consists of our life experiences, although there is a cross-cultural difference between the types of memories which are encoded. Research has shown that memory is malleable and has a tendency to inaccurately reconstruct the past (Loftus and Palmer, 1997), however this does not stop the human mind having an ability to reconstruct past events with great detail.

Research suggests that depressed people have difficulty remembering specific events, instead they are much more likely to over-generalise their memories of specific negative instances into prolonged periods of time which are more consistently negative than they were in reality. The effects of mood on memory have been shown to improve recall if the person is in the same emotional state as they were when the memory was encoded. This means that a person who has become depressed because of a recent event is likely to remember more negative rather than positive memories and therefore prolong depression. Research has shown that depressed people appear to have a bias in the speed in which they recall positive and negative memories, negative memories being much easier to retrieve despite depressed people having no more objectively depressing experiences compared with a person who is not depressed.

There is evidence that suggests that depression is associated with a reverse in the normal trend of recalling more positive memories than negative memories as Lloyd and Lishman (1975) found that the more severely depressed a person was, the quicker the patient retrieved an unpleasant memory. The function brain impairment hypothesis argues that prolonged stress during crucial development stages as a child and adolescent play a key role in recurrent depression. There is some evidence that hippocampal volume, an area involved with memory, decreases as a result of prolonged stress (Cordon et al., 2004). This explanation implies that the onset of depression is determined at an early age and would require early intervention with coping methods for stress to prevent a reduction in the size of the hippocampus and therefore reduce the chances of a person developing depression later in life.

It is important to note that memory can change as a consequence of depression rather than it having a role in causing depression. Williams (1996) found that people who suffer from depression often have difficulty producing specific memories, instead they tend to over-generalise their memories of specific instances. Over-generalised memories can arise from an encoding deficit in which people who are prone to emotional disturbances tend to encode the general themes of situations rather than specific details. It can also arise from problems in retrieval in which people stop short in the search for specific episodes (Kuyken 2006). Memory retrieval can be divided into two categories, one is strategic which a top-bottom process as it requires cognitive effort to be reconstructed. Memory retrieval can also be involuntary as a specific external cue my trigger memory retrieval through a bottom-up process.

Experiencing a negative event could potentially trigger the undesired retrieval of numerous negative memories which would contribute greatly to the onset of depression. According to the limited-cognitive resource hypothesis, depression and post-traumatic stress disorder (PTSD) use up cognitive resources to that manage the retrieval process. This leaves few resources for strategic retrieval, which requires a lot of effort to reconstruct a coherent memory, leaving the person with a series of over-generalised negative memories. Ineffective coping methods have a role to play in the onset of depression, as they can leave the person with encoding difficulties of events arise from emotional disturbance which can in turn lead to over-generalised memory and the faster retrieval of negative memories. The inability to cope with negative events can trigger depression through an emotion based retrieval cue in which the individual will involuntarily recall more negative memories.

References

Cordon, I.M., Pipe, M.E., Sayfan, L., Melinder,A. & Goodman, G.S.(2004). Memory for traumatic experiences in early childhood. Developmental Review,
24, 101–132. Kessler, R.C., McGonagle, K.A., Zhao, S., Nelson, C., Hughes, M., Eshleman, S., Wittchen, H. and Kendler, K. (1994b) Lifetime and 12-month prevelance rates from the National Comorbidty Survey. Archives of General Psychiatry, 51, 8-19. Kuyken, W. (2006). Digging deep into depression. The Psychologist, 19 (5), 278-281. Lloyd, G. G. & Lishman, W. A. (1975). Effect of depression on the speed of recall of pleasant and unpleasant experiences. Psychological Medicine 5, 173-180. Loftus, E.F. and Palmer, J.C. (1974) Reconstruction of automobile destruction: An example of the interaction between language and memory. Journal of Verbal Learning and Verbal Behaviour, 13, 585-9. Williams, J.M.G. (1996). Depression and the specificity of autobiographical memory. In D.C. Rubin (Ed.) Remembering our past: Studies in autobiographical memory. (pp.244–267).