Abstract
Emotion is created by the cerebrum, that is a manifestation of the cerebral functions, and may affect other cerebral functions. This paper discusses two topics on the effects of emotion on memory function in human; one is amygdalar damage affecting emotional memory, and the other is neural basis of dissociative amnesia. Everyday experience suggests that highly emotional events are often the most memorable. Experimental work in animals and humans has demonstrated that the amygdaloid complex plays a crucial role in emotional memory, i.e., memory of events arousing strong emotions. In Alzheimer disease, the amygdala is involved centrally from the initial stage of the disease as well as the hippocampus. By using memory of emotional experience (Hanshin Earthquake) and controlled experimental setting, we demonstrated that emotion reinforced memory retention in patients with Alzheimer's disease, and that the effect is related to intensity of amygdalar damage and is associated with visual memory function. These findings give a clue to the management of people with dementia, and also provide evidence of the amygdala's involvement in emotional memory in humans. Dissociative amnesia usually follows an emotionally stressful event and cannot be attributable to explicit brain damage. It is thought to reflect a reversible deficit in memory retrieval probably due to memory repression. We used fMRI to investigate neural activity associated with memory retrieval in two patients with dissociative amnesia, and found increased activity in the pFC and decreased activity in the hippocampus during seeing faces or names of actually well-known but forgotten people. After treatment, the altered pattern of brain activation disappeared in one patient whose retrograde memories were recovered, whereas it remained unchanged in the other patient whose retrograde memories were not recovered. These findings provide direct evidence that memory repression in dissociative amnesia and suggest that the pFC has an important role in inhibiting the activity of the hippocampus in memory repression.
