Biology subjects

Bassard, A. M.

Publications and source records attributed to Bassard, A. M..

3 recordsLinked to original sources

bioRxiv2022

Electrophysiological Markers of Memory Consolidation in the Human Brain when Memories are Reactivated during Sleep

Human accomplishments depend on learning, and effective learning depends on consolidation. Consolidation is the process whereby new memories are gradually stored in an enduring way in the brain so that they can be available when needed. For factual or event knowledge, consolidation is thought to progress during sleep as well as during waking states, and to be mediated by interactions between hippocampal and neocortical networks. However, consolidation is difficult to observe directly, but rather is inferred through behavioral observations. Here, we investigated overnight memory change by measuring electrical activity in and near the hippocampus. Electroencephalographic (EEG) recordings were made in five patients from electrodes implanted to determine whether a surgical treatment could relieve their seizure disorders. One night, while each patient slept in a hospital monitoring room, we recorded electrophysiological responses to 10-20 specific sounds that were presented very quietly, to avoid arousal. Half of the sounds had been associated with objects and their precise spatial locations that patients learned before sleep. After sleep, we found systematic improvements in spatial recall, replicating prior results. We assume that when the sounds were presented during sleep, they reactivated and strengthened corresponding spatial memories. Notably, the sounds also elicited oscillatory intracranial EEG activity, including increases in theta, sigma, and gamma EEG bands. Gamma responses, in particular, were consistently associated with the degree of improvement in spatial memory exhibited after sleep. We thus conclude that this electrophysiological activity in the hippocampus and adjacent medial temporal cortex reflects sleep-based enhancement of memory storage. Significance StatementSleep contributes to memory consolidation, we presume, because memories are replayed during sleep. Understanding this aspect of consolidation can help with optimizing normal learning in many contexts, and with treating memory disorders and other diseases. Here, we systematically manipulated sleep-based processing using targeted memory reactivation; brief sounds coupled with pre-sleep learning were quietly presented again during sleep, producing (a) recall improvements for specific spatial memories associated with those sounds, and (b) physiological responses in the sleep EEG. Neural activity in the hippocampus and adjacent medial temporal cortex was thus found in association with memory consolidation during sleep. These findings advance understanding of consolidation by linking beneficial memory changes during sleep to both memory reactivation and specific patterns of brain activity.

neuroscience↗

bioRxiv2021

Reactivating Memories from a Mathematical Task over a Period of Sleep

Sleep, especially slow-wave sleep (SWS), has been found to facilitate memory consolidation for many types of learning. Mathematical learning, however, has seldom been examined in this context. Solving multiplication problems involves multiple steps before problems can be mastered or answers memorized, and thus it can depend on both skill learning and fact learning. Here we aimed to test the hypothesis that memory reactivation during sleep contributes to multiplication learning. To do so, we used a technique known as targeted memory reactivation (TMR), or the pairing of newly learned information with specific stimuli that are later presented during sleep. With TMR, specific memories can be reactivated over a period of sleep without disrupting ongoing sleep. We applied TMR during an afternoon nap to reactivate half of the multiplication problems that had previously been practiced. Results showed no effect of TMR on response time or accuracy of multiplication problem solving. Because these results were unexpected, we also used a variation of this paradigm to examine results in subjects who remained awake. Comparisons between the wake and sleep groups showed no difference in response time or accuracy in either the initial test or the final test. Although neither TMR nor sleep differentially influenced multiplication performance, correlational analysis provided some clues about mathematical problem solving and sleep. On the basis of these findings, even though they did not provide convincing support for our hypotheses, we suggest future experiments that could help produce a better understanding of the relevance of sleep and memory reactivation for this type of learning.

neuroscience↗

bioRxiv2021

Targeted Memory Reactivation of Face-Name LearningDepends on Ample and Undisturbed Slow-Wave Sleep

Face memory, including the ability to recall the name of a familiar person, is often crucial in social interactions, and like many other memory functions, it may rely on sleep. We investigated whether targeted memory reactivation during sleep could improve associative and perceptual aspects of face memory. Participants studied 80 face-name pairs, and then a subset of spoken names was presented unobtrusively during a daytime nap. This reactivation preferentially improved recall for those face-name pairs, as modulated by two factors related to sleep quality. That is, the memory benefit was positively correlated with the duration of stage N3 sleep (slow-wave sleep) and with the extent to which cues presented during SWS did not produce a sleep disruption indexed by increased alpha-band electroencephalographic activity in the 5 seconds after a cue. Follow-up analyses showed that a memory benefit from presenting spoken names during sleep was evident in participants with high amounts of SWS or with low amounts of sleep disruption. We conclude that sleep reactivation can strengthen memory for specific face-name associations and that the effectiveness of reactivation depends on uninterrupted N3 sleep.

neuroscience↗