Sleep and Cognition Flashcards
Three main theories about sleep
Cellular restoration
Energy conservation
Consolidation of memory and learning
Sleep deprivation
Lack of sleep affects many cognitive functions including learning and memory
Experiments can target learning or retrieval of info and how sleep deprivation before or after learning affects memory
Sleep before learning (Yoo et al, 2007)
- 28 healthy participants
- Randomly assigned to either sleep control group or sleep deprivation
- It was a 4-day procedure with encoding occurring after the sleep control or deprivation condition
- Investigated whether lack of sleep affects learning and hippocampal activation during learning negatively
- This allows us to conclude any differences are not due to being tired, its due to deprivation during the time of encoding
- fMRI tests were conducted during learning
Findings:
- performance of sleep control group was significantly better than sleep deprivation group
- sleep control group - 85% of picture recognition
- significant difference in brain activation during encoding trials
- activation in hippocampus was significantly reduced
Conclusion:
- lack of sleep before learning reduces ability to encode new data in hippocampus
- lack of sleep compromises learning and hippocampal activation during learning
- sleep before learning is critical
Sleep after learning (Gais et al., 2007)
- deprivation after learning in two groups (deprived and control) measured at three intervals (20 minutes, 24 hours, and 6 months).
- Memorising English-German word pairs
- Experimental group deprived of sleep the first night after learning stimuli
- All tests were done while fMRI was encoded
Findings:
- The rate of forgetting was significantly higher in those who had sleep deprivation
- Subjects remembered more clearly if sleep after learning happened than if it stayed awake
- Lack of sleep straight after learning resulted in increased forgetting and affects hippocampus activation negatively during time of retrieval
- The findings suggest that the medial prefrontal cortex showed long-lasting alterations in memory representations in brain areas which are involved in long-term memory storage because of immediate lack of sleep
Conclusion:
- Lack of sleep after learning will lead to increased forgetting and reduced hippocampus activation during retrieval
Sleep Architecture
Sleep stage (cycle of different stages over the course of a night): dreaming occurs in all sleep stages
Stage one: falling asleep
Stage two: deeper form of sleep, slower activity
Stages three and four: slow-wave sleep, deepest form of sleep we have
REM sleep: another deep form of sleep but brain engages in different types of behaviour, usually during second half of the night
Sleep and motor learning (Walker et al, 2002)
Conducted a study investigating the impact of sleep on procedural memory by having participants learn fast finger tapping sequentially on non-dominant hand
- Two groups- 10am and 10pm - completed test 3 times
-Participants who improved the most are those who got the most stage two sleep (deeper form of sleep, slower activity)
Findings
- The performance of both groups improved after sleep
-Depending on the percentage of stage 2 sleep, performance was affected
-Better improvement if more stage 2 sleep
-Time of day did not affect performance
(Wagner et al, 2004) The number reduction task
Experimenters can determine the time point when insight occurs, when new explicit knowledge of a hidden abstract rule is gained and applied to the problem at hand
- Participants were asked to convert digits and report last digit of conversion
- About 55% of the sleep participants gained insight compared to 20% of wake participants
- Insight was greater in the sleep group therefore sleep in processing this problem overnight
Findings
- In the sleep group – in non-solvers, sleep made RT’s significantly faster
- No effect on RT from sleep for solvers (not quicker but they had greater insight)
When analysing the reaction time improvement of those in the sleep condition and participants who solved the problem and those that did not, it was found that non-solvers brain activity during sleep was focussing on implicit learning (so it was not recoding information to promote insightful behaviour)
Sleep and reasoning (Ellenbogen et al, 2007)
According to Ellenbogen et al, (2007), sleep is essential for boosting the brain
- 56 participants given statements and expected to make inferences from abstract patterns. Repeatedly told statements which form a hierarchy. Then given new pairs.
Findings
- There is not much difference between sleep and wake groups however there are greater differences for two-degree separation
- In sleep group, performance was better for distant pairs (two-degree separation)
Conclusion
- Found that inference performance increased after a period of sleep
Sleep and false memories (Payne et al., 2009)
- Participants study fMRI list tasks then are tested free recall of as many words as possible
- Time of day control was conducted
- Sleep not only helps recall more words in sleep than wake group but also promotes emergence of more false memories in sleep group than wake group
Findings
- Sleep group recalled a higher number of words accurately
- Sleep group also had a higher number of false memory words
This suggests that the brain’s analysis of semantic meaning is better and false memories is a by-product
Conclusion
Sleep does not only make new memories stronger, it also:
- Helps transfer old solutions to new problems
- Gain insight to problems
- Understand relationship between distantly related information
- Extract gist of new memory which may lead to false memory
(Saletin & Walker, 2002)
- Hippocampus encodes new info and integrates to cortical distributes networks
- During sleep, hippocampus replays and reactivates information which allows the cortex to gradually strength the info and connects the new info with existing pieces of information with consistent reactivation
- After sleep, cortical information is fully integrated and hippocampus representation fades away allowing it to encode new information
(Rasch et al., 2007)
- Participants asked to learn location of cars on paper and exposed to odor while learning so association forms between learning of cars and smell
- After sleep, memory is tested for locations
Findings
- Odor cues during sleep can prompt memory consolidation
- New memories used in human during sleep
- fMRI revealed significant hippocampal activation in response to odor re-exposure during SWS
Dreaming and memory (Hall, 1972)
- found people dream about their waking experience and was able to create accurate profiles and histories of psychiatric patients by reading their dream reports
- dreams combine parts of waking experience with elements of recent and older memories
- dreams may represent spontaneous reactivation and the combination of new and old memories
(Wamsley et al, 2010)
- participants had to learn to navigate virtual maze then either took a nap or stayed awake
- all were asked three times to report what they were dreaming or thinking about
- tested again after a nap/wake, and found sleep group improved significantly during the nap than those who did not dream about the maze
- dreaming of maze related to past experience is reflective of the role of sleep in integrating new memories in existing semantic memory
