A depressed person experiences some very specific and extensive problems with memory. The American Psychological Association has acknowledged this negative problem by including impaired memory as one of the signs of clinical depression listed the Diagnostic and Statistical Manual of Mental Disorders. Further, in 2005 the journal "Cognitive Neuropsychiatry" published research findings that summarized the effects of depression on the mental processes involved in memory including attention, sensory processing, awareness and sustained effort.
Attention Impairment
To retrieve memorized information, or to form new memories, people must be able to direct their mental attention to the task. A depressed person lacks the energy required to direct focused attention. She also experiences a decrease in interests and attention is further impaired by a lack of motivation to make the effort needed. A depressed person's attention is also impaired by a deficit in setting priorities. The pessimistic thinking that comes with depression distorts her previously understood and clear priorities, making it difficult for her to focus on the most important things.
Sensory Processing Impairment
The starting point for memorizing information is the sensory awareness of the information and the processing of this information by the brain. A depressed person experiences fatigue while awake, and disruptions in sleep which decrease his brain's ability to accurately and rapidly perform these automatic processes. Lowered serotonin levels further decrease his brain's efficiency at processing this sensory information obtained from his vision and hearing. Essentially, a depressed person's brain is not functioning normally in several key areas required for memory.
Decreased Alertness
Being alert is central to both memory retrieval and memory creation. A depressed person's accuracy in both retrieval and creation of memory is flawed because mental processes are blunted and slowed by poor sleep and fatigue. Her lethargy may become so severe that even her natural startle response may become muted. With arousal this low, her central nervous system is not prepared to engage in the concerted and often difficult tasks involved in memory.
Deficits in Sustained Effort
Recalling information and developing a memory of new information requires sustained effort, especially when the information is of a technical or complex nature. A depressed person's ability to sustain effort is impaired because of two primary distractions. His first distraction is intrusive negative and distressing thoughts, which are symptoms of his depression. These intrusive thoughts vary from one person to the next and the severity may change through the course of depression. Regardless of their content or severity, their intrusive nature disrupts any attempts he makes to sustain effort. The second distraction is his physical aches and pains that accompany depression. As his dopamine levels reduce during depression, the frequency of these distracting somatic sensations increase.
References
- "The impact of clinical depression on working memory" in Cogntive Neuropsychiatry; Gary Christopher and John MacDonald. Nov2005, Vol. 10 Issue 5, p379-399.
- "The Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.); 2000; The American Psychological Association.
- "Understanding Depression: What We Know and What You Can Do About It"; J. Raymond DePaulo Jr. and Leslie Alan Horvitz;2003.
