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- Davidson, Per, et al.
(författare)
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A daytime nap does not increase mnemonic discrimination ability
- 2020
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Ingår i: Journal of Sleep Research. - : Wiley-Blackwell Publishing Ltd. - 0962-1105 .- 1365-2869.
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Tidskriftsartikel (refereegranskat)abstract
- It has been proposed that sleep readies the brain for novel learning, and previous work has shown that sleep loss impairs the ability to encode new memories. In the present study, we examined if a daytime nap would increase mnemonic discrimination (MD) performance. MD is the ability to differentiate between memories that are similar but not identical. Participants performed the Mnemonic Similarity Task (MST) twice, once in the morning and once in the afternoon. The goal of this task is to distinguish stimuli that have been seen before from novel stimuli that are similar but not identical. After the morning MST, participants were randomly allocated into either a sleep or a wake group. The sleep group had a 2-hr nap opportunity, whereas the wake group spent a similar amount of time passively resting. All participants then performed a second MST in the afternoon with a novel set of images. Results did not show any support for increased MD ability after a nap. There was, however, a correlation showing that an increase in sleepiness between sessions predicted a decrease in MD performance. Future work must systematically examine how strong sleep manipulations that are needed for sleep to have an effect on encoding ability, as well as which kind of memory tasks that are sensitive to sleep manipulations. More knowledge about the relationship between sleep and the ability to differentiate similar memories from each other is important because impaired MD ability has previously been reported in various groups in which sleep disturbances are also common.
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| 3. |
- Davidson, Per, et al.
(författare)
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A daytime nap does not increase pattern separation ability
- 2019
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Ingår i: Sleep. - : Oxford University Press. - 0161-8105 .- 1550-9109. ; 42:1, s. 42-42
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Tidskriftsartikel (refereegranskat)abstract
- Introduction A large body of studies has showed that the ability to learn new information is impaired when we are sleep deprived. Pattern separation (PS), the ability to form distinct memories for events that are highly similar and share overlapping features, has also previously been found to be impaired by sleep deprivation. In the present study, we examined if a daytime nap would increase PS performance. Methods 108 young healthy participants came to the lab in the morning and completed the Mnemonic Similarity Task (MST). This task starts with an encoding phase where participants view images of common everyday objects and are asked to classify them as indoor or outdoor objects. During a subsequent memory test, participants view three different kinds of objects; ‘old’ objects that were also present during the encoding phase, ‘new’ objects that have not been seen before, and ‘lure’ objects that are similar to, but not exactly the same as, objects viewed during encoding. The task of the participants during the re-test is to say if the objects presented are ‘old’, ‘new’ or ‘similar’. This test gives two different outcome measures: General Recognition (GR) - the ability to separate old objects from new ones, and PS - the ability to separate similar objects from old ones. After this task, participants were randomly allocated to either a sleep or a wake group. The sleep group had a two-hour nap opportunity and the wake group spent an equal amount of time resting. After this delay interval, participants completed the MST for a second time with a new set of images. Results Results revealed no support for sleep in increasing either GR or PS ability. Within the sleep group, there were no correlations between changes in PS ability and time spent in any sleep stage. Conclusion Previous studies that have found a role of sleep for PS ability has done so using larger manipulation of sleep. Based on the present study however, just a short daytime nap does not seem to have any effect on PS ability.
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| 4. |
- Davidson, Per, et al.
(författare)
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A more generalized fear response after a daytime nap
- 2018
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Ingår i: Neurobiology of Learning and Memory. - : Elsevier BV. - 1074-7427 .- 1095-9564. ; 151, s. 18-27
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to examine how a daytime nap affected the consolidation of fear learning. Participants first underwent fear conditioning during which they were exposed to a large and a small circle. One of these was repeatedly paired with an electric shock (making it the CS+), whereas the other circle was never paired with the shock (the CS−). After a delay interval containing either a nap or wake, participants again viewed the CS+ and the CS− intermixed with eight novel circles that varied in size between the two stimuli seen before, as well as a blue triangle that served as a novel stimulus without prior fear relevance. We examined both fear retention (the difference between the CS+ and the CS−) and fear generalization (responses to the novel stimuli based on their similarity to the original CS+). Contrary to previous studies, results from the participants who acquired a differentiated fear response during the acquisition phase revealed that the wake group showed significantly larger skin conductance responses to the CS+ compared to the CS−, whereas no such difference was present in the sleep group. These results were not driven by differences in explicit memory or by differences in general reactivity. Analyzing responses to the novel stimuli revealed a tendency towards a more generalized response in the sleep group, with no differences between the CS+ and any other stimulus, whereas the wake group showed increased responses to the stimuli depending on their similarity to the original CS+. This effect was however only present when controlling for baseline differences in worry.
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| 5. |
- Davidson, Per, et al.
(författare)
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Does sleep selectively strengthen certain memories over others based on emotion and perceived future relevance?
- 2021
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Ingår i: Nature and Science of Sleep. - : Dove Medical Press Ltd.. - 1179-1608. ; 13, s. 1257-1306
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Forskningsöversikt (refereegranskat)abstract
- Sleep has been found to have a beneficial effect on memory consolidation. It has furthermore frequently been suggested that sleep does not strengthen all memories equally. The first aim of this review paper was to examine whether sleep selectively strengthens emotional declarative memories more than neutral ones. We examined this first by reviewing the literature focusing on sleep/wake contrasts, and then the literature on whether any specific factors during sleep preferentially benefit emotional memories, with a special focus on the often-suggested claim that rapid eye movement sleep primarily consolidates emotional memories. A second aim was to examine if sleep preferentially benefits memories based on other cues of future relevance such as reward, test-expectancy or different instructions during encoding. Once again, we first focused on studies comparing sleep and wake groups, and then on studies examining the contributions of specific factors during sleep (for each future relevance paradigm, respectively). The review revealed that although some support exists that sleep is more beneficial for certain kinds of memories based on emotion or other cues of future relevance, the majority of studies does not support such an effect. Regarding specific factors during sleep, our review revealed that no sleep variable has reliably been found to be specifically associated with the consolidation of certain kinds of memories over others based on emotion or other cues of future relevance.
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| 7. |
- Davidson, Per, et al.
(författare)
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No effect of sleep on the generalization of fear learning
- 2014
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Ingår i: Journal of Sleep Research. - : Wiley-Blackwell Publishing Ltd. - 1365-2869 .- 0962-1105. ; 23
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Objectives: Sleep has been shown to be involved both in emotion regulation and in the active processing of information. We combined these two concepts and tested if sleep affected the generalization of fear learning. Methods: In a fear conditioning paradigm, participants were shown images of a small and a big circle where one of them was paired with an aversive sound, making it the CS+. Fear was measured with skin conductance responses. Participants were then randomly divided into a sleep or a wake group. The sleep group took a 2 h nap while the wake group rested for 2 h. Participants were then exposed to the two circles seen before, combined with 8 novel circles that gradually varied in size from the small one to the big one. We looked at how many circle sizes away from the CS+ that participants still exhibited a fear response, and if this differed between the sleep and the wake group. Results: We found no effect of sleep on the slope of the generalization across the different circles. There was a main effect of circle size, F(1,25) = 10.42, P = 0.01, but no main effect of sleep/wake, F (1,25) = 0.40, P = 0.54, and no interaction between sleep/wake X circle size, F(1,25) = 0.62, P = 0.44. Conclusions: The fear conditioning manipulation worked, with a gradual increase of fear depending on the stimuli’s similarity to the CS+. However, there was no effect of sleep or wake, which could possibly be explained by that just a 2 h nap not being a sufficient sleep manipulation to detect any differences.
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| 8. |
- Davidson, Per, et al.
(författare)
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Sleep and the generalization of fear learning
- 2016
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Ingår i: Journal of Sleep Research. - : Wiley-Blackwell Publishing Ltd. - 0962-1105 .- 1365-2869. ; 25:1, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- Fear conditioning is an important survival mechanism, as is the ability to generalize learned fear responses to stimuli that are similar to the original conditioned stimulus. Overgeneralization of fear learning, prominent in many anxiety disorders, is however highly maladaptive. Because sleep is involved in the consolidation of fear learning, and in active processing of information, the present study explored the effect of sleep on generalization of fear learning. Participants watched a random sequence of pictures of a small and a big circle, one of them coupled with an aversive sound. Then, after a delay period containing either a nap or wake, generalization was examined as participants watched the two circles again, together with eight novel circles that gradually varied in size between the former two. Results showed that the fear response increased as a function of similarity to the conditioned response. However, there was no difference in the degree of generalization between the sleep and the wake group.
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| 9. |
- Davidson, Per, et al.
(författare)
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Suppression-induced forgetting diminishes following a delay of either sleep or wake
- 2020
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Ingår i: Journal of Cognitive Psychology. - : Informa UK Limited. - 2044-5911 .- 2044-592X. ; 32:1, s. 4-26
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the duration of suppression-induced forgetting (SIF), and the extent to which retrieval suppression differs between negative and neutral memories. We further examined if SIF was differently affected by sleep versus wake during the delay interval between retrieval suppression and re-test. Fifty participants first learned to associate neutral words with either neutral or negative images. Then, a subset of the words was shown again, and participants were asked to either recall (Think), or to suppress retrieval of (No-Think) the associated images. Finally, a memory test for all items was performed either immediately after the Think/No-Think (T/NT) phase (No Delay), or after a 3.5 h delay interval containing either sleep or wake. Results revealed a SIF effect only in the No Delay group, indicating that this forgetting effect dissipates already after a 3.5 h delay interval. Negative items were experienced as more intrusive than neutral ones during the T/NT phase.
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| 10. |
- Davidson, Per, et al.
(författare)
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The association between mnemonic discrimination ability and differential fear learning
- 2021
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Ingår i: Journal of Behavior Therapy and Experimental Psychiatry. - : Elsevier Ltd.. - 0005-7916 .- 1873-7943. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- Background and objectives: It is important to be able to learn which stimuli in our surroundings predict aversive outcomes. To maintain emotional well-being, it is similarly important to be able to learn which stimuli predict safety. The ability to discriminate between stimuli that predict danger and safety has been suggested to not only have an emotional component, but also a cognitive one. One such candidate mechanism is mnemonic discrimination (MD), the ability to differentiate between two memories that are similar but not identical. In the present study, we wanted to examine if MD performance helps to explain inter-individual differences in the ability to acquire a differentiated fear response during fear conditioning. Methods: Participants performed a task assessing MD ability, and then underwent a fear conditioning procedure. Fear responses were measured using skin conductance responses (SCRs). Results: Results revealed no support for MD ability being associated with to which degree a differentiated fear response was acquired, or with the time needed to acquire such a response. Limitations: Our only outcome measurement was SCRs. Future studies need to include fear ratings, expectancy ratings and neural responses. Future studies also need to examine this using a stimulus material where the conditioned stimulus and the safety stimulus are more difficult to distinguish from each other. Conclusions: If MD ability has a role in inhibiting overgeneralization of fear learning, this does not seem to be driven by MD already during the initial learning.
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