Sleep & Cognition - PS2021

All animals sleep

three dominant theories why:

- cellular restoration; during sleep cellular spinal fluid is used to wash out waste products in brain - if didn't happen cause alzheimers

- energy conservation; sleep is a way to conserve energy during times when animal not able to look for food e.g. at night when it's too dark to look around for food

-consolidation of memory and learning

not mutually exclusive; could have been cellular restoration at first

lack of sleep affects many cognitive functions, including learning and memory

Yoo et al (2007) sleep deprivation before learning - encoding in fMRI scanner involved memorising pictures. Test involved discriminating studied pictures from unstudied pictures - lack of prior sleep compromises learning and hippocampal activation during learning

Gais et al (2007) sleep deprivation after learning - encoding involved memorising word-pairs. test involved recalling the word-pairs. fMRI measured during encoding and all tests - lack of sleep immediately after learning increases forgetting and compromises hippocampal activation during later retirieval - lack of sleep immediately after laerning leads to long-lasting (permanent?) changes in memory representations in brain areas responsible for long-term storage of memories

So it seems the brain is actively doing something on new memories during sleep. the brain doesn't switch off during sleep

Walker et al (2002)

Sequential finger tapping task on non-dominant hand

AM/PM design to tease apart benefits of time spent awake vs sleep

10am - train/test - awake - test - sleep - test

10pm - train/test - sleep - test - awake - test

Monaghan et al. 2015 Analogical problem solving

9am - source problems - awake - target problems

9pm - source problems - sleep - target problems

Example of a source problem: general attacking a fortness with mines on the road

Example of a target problem: how to target a stomach tumour with a ray that destroys healthy tissue

- Solution accuracy also correlated with sleep duration. More sleep = more accurate solutions to target problems. Sleep facilitates transfer of old solutions to new problems

Wagner et al (2004) Number reduction task

The number is always the same as the solution number

The number of participants who gained the insight was largest in the sleep group

How did task performance change overnight in solvers and non-solvers?

- In solvers, sleep had no impct on the reaction times (RTs) in the task. In non-solvers sleep made RTs significantly faster

- Sleep promoted insight in sovlers and facilitated calculations in non-solvers

Ellenbogen et al. (2007) Inferential knowledge

Premise pairs a>b b>c c>d d>e e>f

Embedded hierarchy a>b>c>d>e>f

Inference pairs; is b>d? c>e? b>e?

Wake group: 9am: train premise pairs - awake - test

Sleep group: 9pm: train premise pairs - sleep - test

24hr delay group: 9pm: train premise pairs - 24hrs - test

Sleep and wake have similar impact on close inference pairs. but a night of sleep boosted on distant (2 degrees of separation) inference pairs

Payne et al (2009) Deese-Roediger-McDermott (DRM) task

9am - study DRM lists - awake - test on lists

9pm - study DRM lists - sleep - test on lists

at study: memories 12 DRM lists

at test: free recall as many of the words as possible

Time of day control groups studies in the morning or in the evening and were tested almost immediately

Sleep does not just make new memories stronger

The sleeping brain continues to process new memories to:

- help transfer old solutions to new analogical problems

-to gain insight to problems

-to compute the relationship between distantly related information

-to extract the gist of new memories (which can lead to false memories)

Saletin and Walker 2012

A: Hippocampus rpaidly encodes new information and integrates it in distributed cortical networds

B: Hippocampal information repeatedly reactivated during sleep -> gradually strengthens corticio-cortical connections

C: Reactivation over time integrates new memories with cortical memories

What do people dream about?

Hall (1972) foudn that people tend to dream about their waking experience -  Hall was able to create accurate profiles and histories of psychiatric patients just by reading large numbers of their dream reports.

Despite impact of waking experience, dreams often incorporate isolated elemetns of waking experience intermingled with fragments of other recent and older memories, Waking experience: When i left work at starbucks, we had so many leftover muffins had to decide what to take home and what to throw away - sleep report: my dad and i go shoping, one store is filled with muffins and i can't decide which one i want

Dreaming may reflect spontneous reactivation, and the brin integating new memories with old memories - Wamsley et al 2010 Dreaming enhances consolidation - sleep group improved during the nap - wake group did not. Those sleepers who reported dreming bout the maze improved signficantly during the nap - imagery and thought of maze task related to past experience - suggests that dreaming is not a simple reiteration of wake experiences in their original form. Instead it reflects sleep's role in integrating new experiences in existing semantic memory

lack of sleep impaires newly encoded memories as well as impairs our ability to encode new memories

sleep enhances many different aspects of cognition, for example

- learning of motor skills

-problem solving and insight

-reasoning

-extracting the gist of new memories

sleeps impact on tehse domains of cognition relies on a dialogue between teh hippocampus and neocortex

- the hippocampus replays new information during slow-wave sleep, allowing the slow-learning neocortex to integrate it gradually with existing knowledge

- dreaming can give us a unique insight into which memories the brain replays during sleep