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The brain without sleep
 - Areas affected by sleep loss map suggest vulnerability across three domains:
- Attention
- Executive Function
- Emotional Regulation
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Cognitive effects of sleep disruption
- Alertness and attention: subjective sleepiness, reduced concentration, delayed response time, attentional lapses, distractibility, task switching
- Cognitive function: lowered visual discrimination, reduced logical reasoning, memory problems, poor decision making and poor judgment, impulsivity and lack of inhibitory control, poor communication, flexible thinking or goal directed behaviours
- Emotional regulation: frustration and irritability, emotional reactivity, poor social interactions
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Cascade model of cognitive function
- Can't have higher functioning if don't have the foundation
- Sleep deprivation affects bottom level and thus affects the levels above
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Two process model of sleep regulation – fluctuations in alertness
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Five physiological determinants of alertness
- 1. acute sleep deprivation: alertness degrades due to time awake
- 2. Chronic sleep deprivation: alertness degrades cumulatively with each day that sleep is inadequate
- 3. Time of day (phase): alertness is markedly worse during night-time hours
- 4. Sleep inertia: alertness is worse upon awakening
- 5. Presence of a sleep disorder: alertness failure can be exarcerbated for those with (un)diagnosed sleep disorders
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Monitoring Alertness and Arousal – objective measures
- Multiple Sleep Latency Test
- Ocular Derived Alertness Outcomes
- Brain Derived Alertness Outcomes
- Biologically Derived Outcomes?
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Multiple sleep latency test
- Bring people to lab and give them 20min window to fall asleep, if they don't then you end the test
- Attempt at 10, 12, 2, 4
- Get an average over the 4 sessions and this gives a marker of how sleepy they are
- 0-5: excessive daytime sleepiness
- 5-10: moderate sleepiness
- Test for narcolepsy
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Monitoring Alertness and Arousal – objective measures
- Ocular Indices of Alertness
- Two muscles in the eye that make it open and shut
- Open: activation of LP and relaxation of the OO
- Shut: inhibition of LP and activation of OO
- Old way of tracking: Sleep deprivation = inability to open eyes with weights on them (i.e., activation of LP/relaxation of OC Obicularis oculi)
- Modern methods: glasses that use Infrared light to show when eyes open/shut.
- High amplitude (how big eyes open?)= much quicker blink
- Drowsy state: same amplitude but slower velocity in the reopening phase
- Ocular changes accurately wake and circadian processes (same curve as circadian rhythm?)
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Monitoring Alertness and Arousal – objective measures: Brain Derived Measures of Alertness
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Biological marker of alertness
Long term goal- saliva/blood
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What is attention?
- Attention is: “the mental ability to select stimuli, responses, memories, or thoughts that are behaviourally relevant, among numerous and varying stimuli that are behaviourally irrelevant”
- Attention allows: “[an organism to] select a subset of available information upon which to focus for enhanced processing”
- Three types of attention:
- 1. Sustained attention:
- 2. Selective attention:
- 3. Divided attention
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Sleep Loss and Attention Failure
- Inattention is the “hallmark” of the sleep deprived state.
- Measured by the Psychomotor Vigilance Task (PVT):
- Must click when the timer starts
- Mean/Median response time (Mean RT)
- – Inattention (Attention Lapse defined as : Response ≥ 500msecs)
- – Slowest 10% of responses
- – Fastest 10% of responses
- – RT variability
- – Time on task decrements
- – Errors of commission
- Good measure of sleep deprivation and of sustained attention but doesn't really reflect how we use attention in real life
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Sleep Loss - Changes in Sustained Attention
- Decrease over night time hours
- Back up day two because of circadian
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Sleep loss – comparable to being legally drunk
17-19hrs awake is comparable to a BAC of 0.05.
21-24hrs awake is comparable to a BAC of 0.08-0.1.
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Sustained attention with acute and chronic sleep loss and time of day
- Combination of all 3
- Acute and Chronic effects of sleep loss on neurobehavioural performance.
- Forced desynchrony protocol (42.85h
- days)
- – Normal sleep:wake = 2:1 ratio (28.57h wake:14.28h sleep)
- – Chronic restriction = 3.3:1 ratio (32.85 wake 10h sleep
- When preloaded with sleepiness due to chronic sleep restriction, the response to acute sleep deprivation is exacerbated; and is most evident during circadian nadir.
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Wake State Instability
- The most consistent findings in sleep loss literature is that sleep deprived performance is unstable
- What is state instability and why does it occur?
- Sometimes you're alert, sometimes you're not.
- Greater number of lapses, the more sleep deprived
- Still get periods of normal reaction time
- What are these ‘lapses’ and why do they occur?
- Due to sleep deprivation
- Due to inability to maintain attention
- Having an eye blink the same time stimulus appears
- Just not processing the stimulus
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Sleep loss and executive function
- Executive functions are a set of processes that are fundamental for the cognitive control of behaviour
- Attentional control (ignore distractors/filtering out irrelevant stimuli)
- Inhibition
- Working memory
- Cognitive flexibility
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Sleep loss leads to enhanced distractibility
- Sixteen young (23.3 y ±2y) adults completed the PVT under four conditions
- - Alert vs sleep restricted (5)
- - With and without peripheral distractors
- PVT Lapses 126% more when sleep deprived
- PVT lapses 321% increase when sleep deprived + distraction
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Sleep loss and Response Inhibition
- Go-no go test
- TSD = Impaired ability to withhold a response.
- Hit rate relatively stable until 2 nights TSD
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Sleep Loss and Cognitive Flexibility
- Convergent (crystallised/known thinking) versus divergent (creative/brainstorm) think: TSD impacts the ability to think laterally, innovatively and flexibly.
- Gave Torrence Test of Creativity: asked to draw using shapes
- TSD = impacted divergent ability across all scales:
- - Flexibility
- - The ability to change strategy
- - Originality
- - Generation of unusual ideas
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Sleep Loss and Planning Ability
- Tower of London – a test of planning ability; get given beads of different colours, must get to target configurations
- Planning time affected by sleep deprivation
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Sleep Loss and Decision Making
- Appreciating a complex situation and avoiding distractions
- Keeping track and updating – DLPFC
- • Thinking laterally and being innovative – DLPFC
- • Assessing risks and benefits – OF, DLPFC
- • Maintaining interest in outcome – Ant. Cingulate
- • Controlling mood and behavior – OF
- • Showing insight – DLPFC
- • Communicating effectively – DLPFC/Premotor/Motor
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Sleep loss and emotional regulation
- 60% increase in amygdala activation
- Three-fold increase in volume of amygdala activated
- Missing the cognitive rationalisation by decreased activation of prefrontal cortex
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Sleep loss and moral decision making
- 3 Types of Dilemmas
- 1. Non-Moral: Dilemmas with no emotional or moral component
- 2. Moral Impersonal: Moral dilemmas with low emotional intensity
- 3. Moral Personal: Moral dilemmas with high emotional intensity
- Patients with ventromedial (frontal lobe) damage were more likely to violate moral personal beliefs
- Took longer to make moral decisions.
- More likely to say "inappropriate" when SD (amygdala response)
- 2. High EQ subjects were less susceptible to judgment shifts as a function of sleep loss
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Sleep loss and economic decision making (social preference)
- • The ‘ultimatum game’: financial decision making game with another person where you have to work together
- First person has to decide how to split money, if second agrees, they keep, if they say no, neither gets money
- SD = No difference in amount offered
- SD = Less likely to accept offer on the
- Ultimatum task if considered “unfair”
- Amygdala
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Sleep loss enhanced emotional reactivity to negative stimuli
- Affect go/no-go test
- Stimuli = Emotional (positive or negative) and Neutral
- SD = more impulsive (reactive) to negative stimuli
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Inter- and intraindividual differences
- Inter: differences between people
- Intra: differences within people
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Evidence of trait-like differential vulnerability
- Two main effects we can see in the
- data:
- 1. Response to sleep loss is stable WITHIN participants, but varied significantly BETWEEN participants
- 2. Stability within participants is task dependent
Evidence of trait-like vulnerability observed in ocular derived measures of alertness
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Sleep in shift workers – why does shift work affect performance?
- The circadian system
- Shift workers attempt to sleep while the circadian system is promoting wake
- Shift workers attempt to stay awake while the circadian system is promoting sleep
- The homeostatic system
- – Shift workers typically don’t sleep much prior to the first night shift and so can experience acute sleep loss
- – Shift workers don’t sleep well between consecutive night shifts, and so experience chronic sleep loss
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Shift-work patterns and accident risk - depends on shift timing
- Night shift has greatest risk
- Long work hours are a risk factor
- Compared to the first 8 h,
- • relative risk increases by ~90% after 10h
- • relative risk increases by ~110% after 12h
Consecutive shifts increase relative risk in cumulative manner
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Impact of the interaction between acute and chronic sleep loss on performance
Pre-loaded Drowsiness from Chronic Exposure to Sleep Loss EXACERBATES Impairment due to Acute Sleep Loss
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Doctors working 24 h straight:
- make 36% more serious medical errors
- make 6 times more serious diagnostic errors
- get ‘needlestick’ injuries twice as often overnight
- report nearly 4 times more fatigue-related errors when working 1-4 24-h shifts/month
- report 300% more fatal adverse events
- had 2.3 times more actual crashes and 6 times more ‘near-crashes’ when driving home after work
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Fatigue-related motor vehicle crashes
- Approximately 20% of all road crashes are attributable to fatigue
- More likely to result in serious injury or death
- Fatigue-related crashes most prevalent among shift workers, those with undiagnosed sleep disorders and young males
- 55% of fall asleep crashes are in people less than 25 years old
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Young versus Older Drivers
- Effect of Sleep loss:
- • Younger adults have 7.37x more lane deviations following SD (p<0.001)
- • Older Adults have 3.49x more lane deviations following SD (p=0.01)
- Younger adults are more vulnerable to sleep deprivation
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Lecture summary
- Alertness underpins all aspects of cognitive function, yielding many tasks vulnerable to sleep loss
- Alertness can be accurately measured subjectively and objectively
- Attention failure is the hallmark of sleep related impairment
- Alertness, attention and executive functions are all vulnerable to sleep loss.
- There is a trait-like differential vulnerability to sleep loss; intra and inter-individual differences are observed
- Loss of sleep impacts safety and performance in operational settings, particularly driving and shift work.
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