J A Horne

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A systematic review of 34 driving studies examined whether people can accurately sense their own drowsiness behind the wheel. Drivers were indeed aware of increasing sleepiness, and that awareness tracked both brain activity measures and actual driving errors such as lane departures. Feeling sleepy while driving is a reliable warning sign, and stopping when that feeling arises could substantially cut crash risk.

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Researchers mapped the wiring of a large portion of the fruit fly brain, cataloguing neurons, cell types, and the chemical connections between them in unprecedented detail. The resulting public dataset covers most of the fly's central brain and introduces improved methods for imaging and reconstructing neural circuits at scale. This connectome gives scientists a reference tool to investigate how specific brain circuits produce behavior.

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Using high-resolution electron microscopy, researchers traced the three-dimensional architecture of the second optic chiasm in the fruit fly visual system, a tangle of axon bundles connecting three visual processing regions. They found that about 19,500 neurons per hemisphere contribute to this structure, with axon bundles inverting their spatial order as they pass between regions. The complex crossed wiring appears to support parallel processing of visual information and likely evolved in multiple steps.

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Scientists used electron microscopy to reconstruct the complete synaptic map of a single odor-processing unit (glomerulus VA1v) in the fly brain, identifying every neuron and connection within it. The work revealed more output neurons than genetic screens had previously found and uncovered new classes of local interneurons with distinct circuit roles. The resulting wiring diagram provides a detailed reference for understanding how the fly brain processes smell.

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This review argues that REM sleep — especially the final REM period before waking — shares close ties with wakefulness and influences appetite, energy balance, and food preferences. The author proposes that REM acts as a physiological fast that suppresses appetite, and that losing this late-night REM may contribute to overeating and weight gain in short sleepers. The paper draws connections between REM sleep, feeding behavior, and potential roles in obesity and eating disorders.

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Researchers reconstructed the synaptic circuits of seven neighboring columns in the fly's visual medulla and compared them to measure how consistently the brain builds the same circuit. Overall error rates were below 1%, showing that development produces highly reproducible wiring, though two specific cell types formed unusually high numbers of self-connections. This establishes a baseline standard of circuit precision that connectomics studies can use going forward.

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A simulator study tested whether sleep-restricted drivers (five hours the prior night) became more distracted compared to normally rested drivers during a two-hour monotonous drive. After restricted sleep, drivers looked away from the road more often and were more likely to drift out of their lane when they did. Drowsiness increases the tendency to become distracted, compounding the danger of fatigue-impaired driving.

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Two studies tested whether losing a third of a night's sleep (five hours instead of the normal amount) hurt tennis serve accuracy in semi-professional players, and whether 80 mg of caffeine could help. Sleep-restricted players landed significantly fewer serves in the target box under both studies, and caffeine at that dose provided no benefit. Adequate sleep is essential for this type of precision skill, and caffeine is not a reliable substitute.

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Using electron microscopy, researchers reconstructed a 379-neuron connectome within the fly's optic medulla and identified the cell types that form a local motion-detection circuit. The synaptic connections onto direction-selective neurons matched predictions about how those neurons detect motion direction. The work demonstrates that circuit-level wiring diagrams can reveal the cellular implementation of specific computations.

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Eleven men with obstructive sleep apnea who were long-term CPAP users skipped one night of treatment, then drove a two-hour afternoon simulator the next day. Going one night without CPAP markedly worsened sleep quality and led to significantly more lane deviations, shorter safe driving duration, and greater brain signs of sleepiness compared to nights with treatment. Patients need to understand that even a single night without CPAP can substantially impair their driving safety.

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Twelve sleep-restricted young men drove a two-hour afternoon simulator course after eating either a light (305-calorie) or heavy (922-calorie) lunch, double-blind. The heavy lunch caused significantly more lane-drifting incidents and stronger EEG signs of sleepiness, with differences emerging about 30 minutes into the drive. A large lunch makes already-sleepy afternoon driving meaningfully more dangerous.

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Young and older men drove a two-hour afternoon simulator course after normal sleep and after sleep restricted to five hours, to compare how age affects vulnerability to fatigue at the wheel. After normal sleep the two groups performed equally, but after sleep restriction younger drivers showed significantly more lane deviations and higher brain-activity markers of sleepiness. Young men are more vulnerable to the driving effects of sleep loss than older men.

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Treated sleep apnea patients and healthy controls of similar age drove a two-hour afternoon simulator after normal sleep and after sleep restricted to five hours. After normal sleep both groups performed equally, but after restricted sleep the apnea patients had a 25-minute shorter safe driving window and applied more compensatory effort to stay alert. Successful CPAP treatment normalizes driving ability under adequate sleep, but sleep apnea patients remain more vulnerable when sleep is cut short.

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Twenty-one sleep-restricted volunteers rated their own sleepiness every two minutes alongside reaction-time tests under identical quiet conditions. After an initial five-minute settling period, self-rated sleepiness tracked reaction time closely and both rose together across the test. When conditions are equivalent, people are quite good at judging their own level of sleepiness.

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Researchers analyzed what people were physically doing during slow-response lapses on the psychomotor vigilance test (PVT), classifying each lapse as eyes open, eyes closed, or looking away. Eyes-open lapses were most common, but all three types increased with greater sleepiness, and lapses lasting over 2.6 seconds were almost certainly accompanied by closed eyes (likely microsleeps). Understanding what drives a lapse improves interpretation of the PVT as a sleepiness measure.

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Researchers analyzed road crash records around 14 motorway service areas in the UK over two to three years to test whether rest stops reduce sleep-related collisions. Within 16 km beyond service areas, sleep-related crashes dropped by 22% compared to the same distance before them, a statistically significant reduction. Service areas appear to help, but they showed the least benefit during the highest-risk hours between 2 and 6 a.m.

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This study tested whether people who report feeling chronically sleep-deprived show objective signs of increased daytime sleepiness on gold-standard measures including the MSLT, PVT, and Karolinska scale. Despite believing they needed more sleep, the self-reported sleep-deficit group did not fall asleep faster or perform worse on any objective measure. Feeling like you need more sleep is largely unrelated to measurable daytime sleepiness.

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Researchers applied Drury's two-component inspection model to a simplified X-ray luggage screening task in 12 younger and 12 older participants learning the task over multiple sessions. The model reliably captured performance improvement over training, with the decision component improving more than the search component, and age did not significantly affect either component separately. The model is a useful tool for evaluating speed-accuracy tradeoffs in security screening.

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A survey of over 10,000 adults asked about sleep length, desired sleep, and what they would do with a free hour of time. About half reported wanting more sleep, but this desire was unrelated to daytime sleepiness scores, and most people chose waking activities over sleep when given a free hour. Wanting more sleep appears to reflect stress and desire for time off rather than genuine physiological sleep need.

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Sixteen sleep-restricted young adults completed a reaction-time task after drinking decaffeinated coffee, once while being told it contained caffeine (placebo) and once with no suggestion. The placebo condition produced significantly fewer lapses and faster reactions during the first two 30-minute sessions. Belief that you have consumed caffeine is enough to improve performance in moderately sleepy people.

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Researchers examined how loss of the synaptic protein cysteine string protein (CSP) affects the structure and function of neuromuscular junctions in Drosophila larvae. Fly larvae lacking CSP had proportionally fewer synaptic boutons and reduced neurotransmitter release, but the number of synapses per bouton and the pool of docked vesicles remained normal. CSP promotes both synaptic growth and neurotransmitter release through independent signaling pathways.

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Ten sleep-restricted adults were exposed to a mobile phone in talk, listen, standby, or sham mode for 30 minutes before a 90-minute sleep opportunity. Talk mode significantly delayed the time to fall asleep compared to listen and sham modes, and this was also reflected in frontal EEG activity sensitive to sleep onset. The specific microwave pulse pattern used during phone calls may interfere with the brain's transition into sleep.

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Sixteen sleep-restricted young adults completed a 30-minute reaction-time task with and without an attractive television in their peripheral vision. Sleep restriction increased the number of times participants turned to look at the TV and increased the number of performance lapses, especially in the first 10 minutes. Sleepiness makes people more prone to distraction, which has direct implications for safety-critical tasks.

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Ten sleep-restricted participants drank either a popular energy drink (high sugar, low caffeine) or a matched sugar-free, caffeine-free control and then performed a reaction-time task for 90 minutes. The energy drink did not alleviate sleepiness and actually produced slower reactions and more lapses in the final 30-minute session. High-sugar, low-caffeine energy drinks may worsen sleepiness rather than help.

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Sleep-restricted young men drove a two-hour evening simulator run after consuming alcohol to blood levels around half the UK legal limit. Alcohol alone did not impair evening driving, but when combined with sleep restriction it significantly worsened lane drifting, subjective sleepiness, and EEG measures across all three indices. Even legally modest alcohol intake creates a dangerous combination with sleep loss regardless of time of day.

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Researchers investigated whether the endocytosis that persists in Drosophila synapses lacking synaptojanin and endophilin represents a "kiss-and-run" mechanism or a slowed version of the classical clathrin pathway. Multiple lines of evidence — including FM1-43 dye loading and dynamin function — showed that vesicles undergo full fusion and re-formation even in the mutants. There is no genetic support for kiss-and-run endocytosis at these synapses; what persists is an impaired form of classical endocytosis.

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This analysis of EEG, subjective sleepiness, and lane drifting from 38 sleep-restricted young adults driving an afternoon simulator found that subjective sleepiness and brain EEG measures of sleepiness tracked each other closely and both tracked driving errors. Drivers had genuine awareness of their physiological sleepiness state throughout the drive. Drowsy drivers know they are sleepy, which supports the value of public messaging to stop driving when feeling tired.

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This study measured EEG activity at 7–8 Hz during relaxed presleep wakefulness in younger and older adults and compared it to performance on neuropsychological tasks tied to left frontal brain function. Only the 7–8 Hz frequency range at the left frontal EEG site predicted performance on planning and verbal fluency tasks, and the bedtime relaxed recording was a better predictor than daytime recordings. Presleep frontal EEG may serve as a low-noise marker of left prefrontal cognitive function.

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Twenty sleep-restricted men drove a two-hour afternoon simulator having consumed alcohol over 90 minutes earlier, so that breath alcohol was near zero at the start of the drive. Despite near-zero breath alcohol, the alcohol group initially showed more lane-drifting incidents than the no-alcohol group, and subjective sleepiness did not reflect this impairment. Breath alcohol readings at or near zero do not mean a driver is unimpaired, especially when combined with prior sleep loss.

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This study used nonlinear EEG analysis to examine how different brain regions interact during the first stage of deep sleep in young versus older adults. Older adults showed significantly more interaction between the left prefrontal cortex and the right parietal region during slow-wave sleep delta activity than younger adults. This compensatory pattern mirrors what is seen in young adults after sleep deprivation, suggesting that healthy aging and sleep loss affect the brain in similar ways.

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Women drivers drove a two-hour afternoon simulator after normal or restricted sleep and after alcohol or a placebo drink, mirroring a prior study in men. Unlike men, women showed no impairment from alcohol alone, but alcohol combined with sleep restriction caused profound impairment — and women, unlike men, remained aware of their increased sleepiness. Women seem more sensitive to low-dose alcohol when already fatigued, but their better self-awareness may partly explain their lower rates of sleep- and alcohol-related crashes.

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This observational study tracked all prisoners entering Dartmoor prison over three and a half years to assess hepatitis C screening uptake and outcomes along the care pathway. Of 3,034 entries, only 12% were screened; of those testing seropositive, 79% were confirmed virus-positive, but only 27% had a liver biopsy and just two prisoners were ultimately eligible for treatment. Screening uptake and follow-through were very low, with major drop-off at the prison-to-specialist-care handoff.

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Twelve young men drove a two-hour afternoon simulator after normal or restricted sleep, with or without alcohol at about half the UK legal limit. Sleep restriction and alcohol each worsened driving on their own, but together they caused significantly greater lane drifting and EEG signs of sleepiness, without a corresponding rise in subjective sleepiness. Drivers don't feel the added impairment when alcohol combines with fatigue, making this combination especially dangerous.

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Sleep EEG recordings were taken from 24 healthy older adults (61–75 years) and correlated with their performance on neuropsychological tests sensitive to the prefrontal cortex. Slow oscillation power (0.5–1.0 Hz) specifically in the left frontal EEG channel during the first deep sleep period predicted performance on planning and verbal fluency tasks, but not on tasks tied to other brain regions. Low-frequency frontal sleep EEG may be a non-invasive marker of prefrontal brain health in older people.

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Researchers examined the role of the protein Endophilin at photoreceptor synapses in Drosophila, where sustained neurotransmitter release demands efficient vesicle recycling. Fly photoreceptors lacking Endophilin accumulated clusters of late-stage endocytic vesicles and failed to release neurotransmitter normally, but showed no defect at the earlier membrane-bending step. Endophilin is required for a late step in the synaptic vesicle recycling pathway, not the initial membrane curvature step.

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In twelve older adults, EEG recordings during both waking thinking tasks and home sleep were analyzed to find links between daytime frontal brain activity and early-night deep sleep. Activity specifically in the 7–8 Hz range at the left frontal electrode during relaxed presleep wakefulness correlated with slow oscillation power during the first period of deep sleep. The findings suggest that daytime mental activity in the prefrontal cortex is reflected in how the brain reorganizes during early deep sleep.

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Twelve sleep-restricted young adults received either a well-known energy drink (80 mg caffeine plus other ingredients) or a matched placebo drink mid-drive in a two-hour afternoon simulator. The energy drink significantly reduced lane-drifting incidents and subjective sleepiness for the first 90 minutes after consumption. An energy drink with 80 mg caffeine is an effective short-term countermeasure for drowsy driving under afternoon sleep-restriction conditions.

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Eleven sleepy participants drove an interactive car simulator and received either a glucose-based energy drink or a matched control drink without the active ingredients, double-blind. The energy drink significantly improved lane-keeping and reaction time, particularly in the first hour after consumption. An energy drink containing caffeine, taurine, and glucuronolactone reduces sleep-related driving incidents in drowsy drivers.

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Sleep-restricted drivers completed two-hour afternoon simulator drives with and without a secondary auditory reaction-time task to test whether RT could measure driver sleepiness. Reaction time remained flat while EEG and lane drifting worsened over the drive, and the RT task mainly served to stimulate drivers and reduce monotony rather than reflect their sleepiness level. Drivers' own self-ratings of sleepiness were a more valid indicator of fatigue than the secondary RT task.

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Forty young adults were split into sleep-deprived and control groups and given a task testing both face recognition memory and temporal (recency) memory, with caffeine or placebo and a distracting interpolated task. Sleep deprivation selectively impaired recency memory — knowing the order in which things were seen — while leaving basic recognition intact, and caffeine did not restore the recency deficit. Sleep loss specifically damages temporal memory, the ability to remember when events occurred, independent of whether you can remember that they occurred.

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In two independent studies, young drivers drove a two-hour early morning simulator (6–8 a.m.) after either restricted sleep or no sleep, having taken 200 mg caffeine or placebo 30 minutes before. After restricted sleep, caffeine significantly reduced lane incidents and subjective sleepiness for the full two hours; after no sleep, it helped for only 30 minutes before drowsiness overwhelmed it. Two to three cups of coffee can meaningfully reduce early morning drowsy driving after a short night, but not after a full night without sleep.

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This review examined how sleep deprivation affects decision making across a range of task types. Simple, dull, rule-based tasks are often unaffected because interest and effort compensate, but sleep deprivation reliably impairs responses to the unexpected, innovative thinking, plan revision, and effective communication. Real-world decision makers — managers, military commanders — who lose sleep face specific vulnerabilities that standard lab tasks fail to capture.

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This theoretical paper reviews three overlapping hypotheses about REM sleep and proposes that REM is best understood as a primitive default state of non-wakefulness that preceded deep sleep in evolution. REM tones up the sleeping cortex, can substitute for wakefulness, inhibits motor and emotional systems, and is replaceable by wakefulness without lasting harm. Rather than being essential for memory consolidation or recovery, REM may function primarily as a calming waking-antagonist that fills time when true sleep is absent.

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This study compared neuropsychological test performance across young, middle-aged, and older adults and also in young adults after 36 hours without sleep, using tests designed to tap prefrontal function. Sleep deprivation in young adults produced deficits similar to those seen in healthy people around 60 years old. Sleep deprivation may serve as a useful model for studying the prefrontal cognitive changes of normal aging, though a sleep-deprived brain is not the same as an aged one.

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Ten sleep-deprived participants played a realistic marketing decision-making game requiring flexible thinking and plan updating, compared to rested controls. Sleep-deprived players showed more rigid thinking, more repetitive errors, and an eventual collapse of their performance despite high motivation, while rested players continued to improve. One night without sleep specifically impairs innovative and flexible decision making in real-world-style tasks, even when basic information comprehension is intact.

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Sixteen sleep-restricted young adults drove a 2.5-hour afternoon simulator and, after the first 30 minutes, received one of three conditions: cold air to the face, radio, or no treatment. Neither cold air nor radio significantly reduced lane-drifting incidents or EEG sleepiness markers, though radio briefly reduced subjective sleepiness ratings. Common in-car countermeasures like cold air and radio are poor substitutes for caffeine or a nap and at best buy a driver a few minutes to find a safe place to stop.

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Twenty-eight sleep-restricted young drivers drove a two-hour afternoon simulator and were asked to rate their sleepiness and their perceived likelihood of falling asleep throughout the drive. Major lane incidents — indicating actual sleep episodes — were consistently preceded by extended periods of self-reported increasing sleepiness. Drivers cannot fall asleep at the wheel without a sustained period of growing sleepiness they are aware of, but some need better education that extreme sleepiness very likely leads to falling asleep.

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Twenty young adults were randomly assigned to either 36 hours of sleep deprivation or normal sleep and then completed two novel, short language tasks known from brain imaging to rely on the prefrontal cortex. Sleep-deprived participants performed significantly worse on both tasks, which required generating novel responses and suppressing habitual ones. Sleep loss impairs the prefrontal cortex's ability to produce innovative language responses, even on brief, interesting tasks given for the first time.