A study led by researchers at Beth Israel Deaconess Medical Center and Boston College offers new insights into the specific components of emotional memories, suggesting that sleep plays a key role in determining what we remember and what we forget.
Reported in Psychological Science, the findings show that a period of slumber helps the brain selectively preserve and enhance those aspects of a memory that are of greatest emotional resonance, while at the same time diminishing the memory’s neutral background details.
The authors tested 88 study participants who were shown scenes that depicted either neutral subjects on a neutral background (a car parked on a street in front of shops) or negatively arousing subjects on a neutral background (a badly crashed car parked on a similar street). The participants were then tested on their memories of both the central objects in the pictures and the backgrounds in the scenes. In this way, memory could be compared for the emotional aspects of a scene (the crashed car) versus the nonemotional aspects of the scene (the street on which the car had crashed.)
Subjects were divided into three groups. The first group underwent memory testing after 12 hours spent awake during the daytime; the second group was tested after 12 nighttime hours, including their normal period of nighttime sleep; and the third baseline group was tested 30 minutes after viewing the images, in either the morning or evening.
The results revealed that study subjects who stayed awake all day largely forgot the entire negative scene they had seen with their memories of both the central objects and the backgrounds decaying at similar rates. However, among the individuals who were tested after a period of sleep, memory recall for the central negative objects (i.e., the smashed car) was preserved in detail.
“After an evening of sleep, the subjects remembered the emotional items [smashed car] as accurately as the subjects whose memories had been tested only 30 minutes after looking at the scenes,” explains study author Elizabeth Kensinger, PhD, an assistant professor in the College of Arts and Sciences at Boston College. “By contrast, sleep did little to preserve memory for the backgrounds [i.e., street scenes] and so memory for those elements reached a comparably low level after a night of sleep as it did after a day spent awake.”
— Source: Beth Israel Deaconess Medical Center
