Sleep, dreams and consciousness

What is the behavioural definition of sleep?

• a condition that typically recurs for several hours every night characterised by:

  • immobility

  • reduced response to sensory stimuli

  • rapidly reversable

What is the main way to help record sleep?

• electroencephaly

  • characterise brain state by using elecrtodes to record electrical activity of brain

What is needed to best accurately describe sleep state?

• polysomnograph

  • containing EEG, EOG, EMG

  • need brain, eyes and muscle tone

What are brain waves like as go into sleep through stages?

Do we have intrinsic circadian rhythm?

• yes

  • if mouse put in complete darkness they still have very similar sleep wake cycle

  • not quite 24 hours (around 23)

  • something in nervous system regulates

What is the circadian pacemaker?

suprachiasmatic nucleus

What did Siffre (1975) show?

• absence of external cues significantly altered his circadian rhythm

• When he returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was.

• This suggests that his 24-hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was, and leading to his thinking that fewer days had passed.

What did Duffy et al. (2001) find?

• ‘morning people’ prefer to rise and go to bed early (about 6 am and 10 pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am).

• This demonstrates that there may be innate individual differences in circadian rhythms, which suggests that researchers should focus on these differences during investigations.

How can we see the effect of the SCN?

lesions and transplants - a level study look

What did Morgan (1955) show?

• bred hamsters so that they had circadian rhythms of 20 hours rather than 24

• SCN neurons from these abnormal hamsters were transplanted into the brains of normal hamsters

• subsequently displayed the same abnormal circadian rhythm of 20 hours,

• showing that the transplanted SCN had imposed its pattern onto the hamsters

What did Skene and Arendt (2007) suggest tho?

• claimed that the majority of blind people who still have some light perception have normal circadian rhythms whereas those without any light perception show abnormal circadian rhythms

• this demonstrates the importance of exogenous zeitgebers as a biological mechanism and their impact on biological circadian rhythms

• supports role of melanopsin

What are the molecular mechanisms of the circadian rhythm?

What is photopic entrainment of the circadian rhythm?

add the brain arousal bits that outline the levels of different neurotransmitters at different points of sleep

Role of melatonin?

• When light hits the retina, it signals the brain's internal clock (the suprachiasmatic nucleus, or SCN) to halt melatonin production

• As evening approaches and sunlight fades, the SCN allows the pineal gland to start releasing the hormone.

• peeks at 4am to keep asleep

Why do we go to sleep?

• sleep pressure and circadian rhythm

• homeostatic drive regulates need for sleep

  • slow wave activity increases in proportion to duration of wakefulness in day then progressively decreases during sleep

What did Purves et al show?

• effect of sleep deprivation in rats

• rotating platform so one rat sleeps the other can’t

• rat dies

• haven’t controlled for stress

What did Everson et al (1989) do?

• when rats were prevented from sleeping consistently, it was found that, although their food intake increased, their weight decreased and they died after around a month

• before death, their ability to regulate body temperature and metabolic needs was impaired and they developed conditions like stomach ulcers and internal haemorrhages

• shows how important sleep must be in lots of different functions and necessary for survival if lack of it can even lead to death

• study didn’t control for the stress of being hit by the glass to wake them up however which could have impacted some of the results seen

Who spent 264 hours awake and how did it impact him?

• Randy Gardner 1963

• slurred speech, hallucinations, delusions and more

• after one week though back to normal

• but years later reported debilitating insomnia

What are possible effects of sleep deprivation in humans?

• fatigue

• irritability

• impaired memory

• hallucinations

• tremor

Suggested functions for REM sleep and vivid dreaming?

• memory consolidation and transfer

• unlearning of ‘parasitic’ memory traces

• reinforcement of innate behaviours

  • maybe rehearsal draws out patterns

What did Karni et al (1994) do?

• training participants to identify the orientation of lines in their peripheral field presented for a small amount of time

• saw that with repeated practice, participants got better and improved in their identification more between evening and morning

• when deprived of REM sleep however their learning did not improve but when deprived of non-REM sleep, their performance was enhanced

• double dissociation suggests that specifically the REM section of sleep is involved in consolidating information learnt through the day, forming memories and improving performance.

• INTERPRET

  • Perceptual learning-the improvement of perceptual skills through practice-is a type of human learning that may serve as a paradigm for the acquisition and retention of procedural knowledge

Why can we assume that memory and cognitive abilities is not all REM sleep though?

• lots of different animals eg dolphins have little to no REM sleep

• still capable of forming memories and other cog functions

Do all animals have REM sleep?

no - humans and some others do

What effect does selective REM sleep deprivation have?

• little or no obvious effect on behaviour

• impair memory performance but these interventions also affect non REM sleep

• MAO inhibtors cause littel or no REM yet show no obvious memory impairement after months or years

What did Huber et al (2004) suggest?

What is slow oscillation sleep suggested to be involved in?

• potentiating memory

What did Tononi and Cirelli (2003) suggest?

• While awake, synapses are strengthened through long term potentiation due to learning and new experiences and it is proposed that during slow wave oscillation sleep, synaptic consolidation and downscaling takes place, increasing the signal to noise ratio

Where does evidence for this come from?

Vyazovskiy et al (2008)

• Molecular and electrophysiological evidence for this comes from evoked cortical responses from stimulation within a rat’s cortex as well as measuring of proteins associated with synaptic strength, in which periods of sleep were associated with a net decrease of cortical synapse strength

What did Marshall et al (2006) do?

• Declarative learning

  • Giving word list for example

• Non declarative

  • Eg motor task

• Kept in lab while go to sleep

• Strap electrode

• When enter slow wave

• Apply transcranial to see if improve

• Boosted

• No improvement in non but improvements in declarative

 

Involved in consolidating, optimise retrieval

Is evidence for memory and consolidation stronger in REM or nonREM sleep?

non REM

(REM more controversial)

• perhaps REM is more for non-declarative kinda stuff??