NEW YORK, Feb 22 (Reuters Health) -- The emotional impact of a particular image or event appears to have a profound influence on its place in long-term memory, researchers conclude.
The amygdala -- a part of the brain that plays a role in emotion -- "is important in modulating memory for events according to their emotional importance, regardless of whether the nature of the emotion is pleasant or aversive," conclude Dr. Stephen Hamann and colleagues at Emory University in Atlanta, Georgia. Their findings are published in the March issue of Nature Neuroscience.
The authors presented 10 healthy male volunteers with a series of pictures. Some of the images were meant to evoke pleasant or unpleasant responses (for example, pictures with sexual or gastronomic appeal, or pictures depicting mutilated bodies or frightening animals). Other pictures were 'neutral' (plants, rooms). Others were 'interesting' but were thought to have little or no emotional impact (a picture of a chrome rhinoceros, an exotic festival).
As each man viewed each picture, the researchers conducted positron emission tomography (PET) scans of brain activity.
As expected, the most emotionally potent scenes elicited the highest levels of amygdala activity.
Four weeks later, the men were quizzed as to their memory of the various pictures. The authors report that "long-term... recognition memory was substantially enhanced for the pleasant, aversive, and interesting pictures relative to the neutral pictures." They note that amygdala activity and memory retention was equally strong for both pleasant and unpleasant images.
The amygdala is thought to enhance memory through its interaction with a prime memory center, a part of the brain called the hippocampus. PET scans conducted during the study showed that emotionally loaded images also elicited high levels of activity in the hippocampus.
The Atlanta team speculate that the emotion-memory connection may have evolutionary roots. Pleasurable images connected with activities such as sex or food consumption, or frightening images linked with violence or danger "are generally more important than neutral stimuli for reproductive success," the authors point out.
SOURCE: Nature Neuroscience 1999;2:289-293.
