The categorical effect of negative emotion on memory before and after sleep deprivation

Human memory tends to bias negative over neutral information. Recent evidence suggests that this bias may be due to a categorical effect of emotionally salient information, which diminishes when negative information is less frequent. Moreover, sleep loss has been shown to impair memory. Here, we aimed to replicate this categorical-over valence-bias for emotional information and determine the influence of total sleep deprivation (TSD) on this effect.

Forty-four healthy adults completed two learning-and-memory tasks: once before and once after a night of TSD. In each task, they were presented with 100 words ranging from neutral to negative. Participants were randomized into a "high" (50 % of words were negative) or "low" (12.5 % negative words) frequency condition. Recognition memory was assessed after a brief delay.

Contrary to our hypothesis, we did not observe a shift in negative memory bias based on frequency condition. Before TSD, participants in both conditions ("high" and "low") recalled more negative words than neutral words. Memory was impaired after TSD, for both negative and neutral words, yet a similar negative memory bias persisted across both the high and low frequency conditions, as measured by hit rate and sensitivity. Despite an absence of interaction between valence and condition, we observed a condition-related difference after TSD, with participants in the "low" condition adopting a more liberal response strategy, demonstrating a greater tendency to label all words as old compared to those in the "high" condition.

A significant memory bias for negative words was present for both frequency conditions, both before and after TSD. While we were unable to replicate the loss of an emotional memory bias with altered frequency, we did find some evidence that frequency may interact with sleep loss to influence response strategy.