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Cited by 2Sleep and Wakefulness ResearchTraumatic Brain Injury and Neurovascular DisturbancesTraumatic Brain Injury Research

Effects of Traumatic Brain Injury on the Orexin/Hypocretin System

Open access
Somach, Rebecca T., Lim, Miranda M., Cohen, Akiva S.·2025·Neurotrauma Reports
DOI 10.1089/neur.2024.0111PMC PMC12040569
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Abstract

Traumatic Brain Injuries (TBIs) are known to cause a myriad of symptoms in patients. One common symptom after injury is sleep disruptions. One neuropeptide system has been studied repeatedly as a potential cause of sleep disruptions after TBI- the orexin/hypocretin system. Orexin promotes wakefulness and arousal while disrupting the orexin system causes increased sleepiness and narcolepsy. Studies of TBI in human and animal subjects have shown that TBI affects the orexin system. This review serves as an overview of how TBI affects the orexin/hypocretin system, including structural and functional changes to the neurons after injury. This review is the first to include studies that examine how TBI affects orexin/hypocretin receptors. This review also examines how sex is accounted for in the studies of the orexin system after TBI.

AI snapshot

Written from the paper’s full text.

TL;DR

This narrative review updates evidence that traumatic brain injury disrupts the orexin/hypocretin system in humans and animals, affecting CSF orexin levels, orexin neuron number and physiology, and orexin receptor expression. It also emphasizes that female subjects are underrepresented in this literature and that study heterogeneity limits comparisons.

Key findings

  • Human CSF studies report low orexin after TBI: in Baumann et al. 2005, 37/44 patients (84%) had low CSF hypocretin, including 30/31 severe and 7/8 moderate TBI patients; in Baumann et al. 2007, 25/27 patients had low levels acutely, 13/27 had undetectable levels, and at 6 months 17/21 had normal levels while 4 remained low. Ripley et al. 2001 found 6/7 craniocerebral trauma patients had low orexin, and Arii et al. 2004 found 3/3 children with head trauma had low or intermediate orexin.
  • Human postmortem studies found reduced orexin neurons after severe TBI: Baumann et al. 2009 reported a 27% decrease in hypocretin neurons in 4 TBI patients, and Valko et al. 2015 reported a 21% loss in 12 TBI patients.
  • Animal findings are mixed: some studies report reduced orexin neurons after injury, some report no significant change, and one reported an increase; orexin neuropeptide may increase acutely between 6 and 24 h post-injury and then decrease after 24 h. Functional studies found reduced cFos in orexin neurons after forced wakefulness, decreased glutamate density in synapses onto orexin neurons, reduced glutamatergic afferent activity, and increased GABAergic afferent activity.
  • Orexin receptor expression after TBI is also mixed, with some studies reporting increases and others decreases depending on brain region and timing; Mihara et al. 2011 found orexin receptor expression in microglia at 24 h and in microglia and neurons at 7 days. Sex is understudied: 9 of 25 reviewed studies included women or female animals, human studies had 0–43% women, and 5 of 19 animal studies used female animals.

Methods

  • Narrative review, not preregistered; articles were identified via PubMed searches using keywords such as TBI, head injury, orexin, orexin receptors, OXR, OX1R, and hypocretin, plus citation searching. The authors state they did not use a formalized systematic review search strategy.
  • The review summarizes human and animal studies of TBI and orexin in Table 1, including species, age or weight, sex, injury method, injury severity, and time between injury and measurement.
  • Kousi et al. 2021 is acknowledged as within scope but excluded from Table 1 because the authors judged it lacked sufficient control subject data.

Limitations

  • Stated: this is a narrative review without a formalized search strategy; the field is limited, so the authors considered a narrative review sufficient. Human studies quantifying orexin neurons are after severe TBI and cannot determine what happens immediately after mild or moderate TBI. Animal studies vary in injury method, species, age, timing, and severity, which likely contributes to inconsistent outcomes. Some studies do not control for circadian timing, and some receptor findings are qualitative rather than quantitative.
  • Evident from the text: human samples are often very small (e.g., 4 TBI patients, 12 TBI patients, 3 children), sex representation is low, and most animal studies use only male animals, limiting generalizability. The heterogeneity across models and outcome measures also prevents direct comparison or meta-analytic synthesis.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1089/neur.2024.0111

Cites

126 of 126 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

82 of 147 cited sources checked · 45 supported · 6 flagged · accuracy not yet measured

  • Premisecitation

    Several studies found an increase of orexin receptors compared to sham-injured animals after TBI.

    “Several studies found an increase of orexin receptors compared to sham-injured animals after TBI,75–79,89”
    Quote in the paperNot a substantial claim4 of 6 sources checked
    • cites [75] source
    • cites [76] source

      The Animal model section describes the control rats as receiving no interventions, not a sham injury. The Western blotting section reports higher hypothalamic OX1R in the TBI-only group than in controls at 6 and 24 hours, but lower OX1R at 12 hours. Thus, the paper supports an increase at some time points, not an unqualified increase compared with sham-injured animals. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [77] source

      The Results section (“tDCS promotes the expression of OXA and OX1R in TBI rats”; page unavailable) reports the opposite comparison: OX1R receptor expression was significantly lower in TBI rats than in sham rats. OX1R expression increased after tDCS treatment, not after TBI alone. (LLM, conf=0.92)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [78] source
    • cites [79] source
    • cites [89] source
  • Premisecitation

    In Baumann et al. 2007, 4 of 21 patients had low CSF hypocretin levels 6 months after TBI.

    “Low CSF hypocretin levels, as defined as less than 320 pg/mL, were found in 4 of 21 patients 6 months after TBI.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
  • Premisecitation

    Some studies show no significant differences in orexin neurons between injured and sham-injured animals.

    “Some studies show no significant differences in orexin neurons between injured and sham-injured animals.44,67,69,71,74”
    Quote in the paperNot a substantial claim4 of 5 sources checked
    • cites [44] source
    • cites [67] source
    • cites [69] source

      The Methods and Results (page not available in our copy) compare sleep patterns in injured and sham-injured mice, not orexin neurons. The Discussion mentions the orexin signaling system as a possible contributor to post-injury sleepiness, but reports no comparison of orexin neurons between the groups (searched: orexin neurons, hypocretin, cell counts). (LLM, conf=0.76)

      Experimental — accuracy not yet measured
    • cites [71] source
    • cites [74] source
  • Premisecitation

    Some studies report a significant reduction of orexin neurons after injury.

    “Some studies report a significant reduction of orexin neurons after injury.45,48,73”
    Quote in the paperNot a substantial claim1 of 3 sources checked
    • cites [45] source
    • cites [48] source
    • cites [73] source
  • Premisecitation

    In Baumann et al. 2007, 25/27 patients had low CSF hypocretin after acute injury (1-4 days post-injury).

    “25/27 patients had low levels of CSF hypocretin after acute injury (1–4 days post-injury).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
  • May combine two claims. 30
  • Classified as probably not a substantial claim. 12
  • The quote only partly states this claim. 1

  • May combine two claims.

    Premisecitation

    Orexin neurons are both necessary and sufficient for wakefulness.

    “Orexin neurons are both necessary and sufficient for wakefulness.”
    Quote in the paperSubstantial claim5 of 10 sources checked
    • cites [32] source

      The Results (page not provided) show that administering orexin A to rats increased arousal during the second and third hours after dosing. This supports a narrower claim that the peptide can promote wakefulness, but the paper does not show that activating orexin neurons is sufficient for wakefulness or that those neurons are necessary for it. (LLM, conf=0.87)

      Experimental — accuracy not yet measured
    • cites [33] source
    • cites [34] source

      The Abstract links narcolepsy, which involves excessive daytime sleepiness and sleep attacks, to loss of hypocretin (orexin) neurons. The Discussion concludes that these neurons are lost in narcolepsy. This supports a role in normal sleep–wake regulation, but does not establish that the neurons are either strictly necessary or sufficient for wakefulness. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
    • cites [35] source
    • cites [36] source

      In ‘Activity and signalling’ (page unavailable), the review reports that stimulating orexin neurons rouses mice from sleep. In ‘Poor maintenance of wakefulness’ (page unavailable), it says orexin-null mice still have wake bouts, though these are shorter than in controls. The source therefore supports a wake-promoting role, but not the claim that orexin neurons are necessary for wakefulness itself. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [37] source
    • cites [38] source
    • cites [39] source

      The sleep/wake findings report awake episodes in orexin-null mice, so orexin is not necessary for wakefulness itself. The Conclusions say orexin helps maintain wakefulness through OX2R signaling, a narrower point. The paper also does not establish that orexin neurons are sufficient for wakefulness. (LLM, conf=0.87)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [40] source

      The Results (page unavailable) report that orexin knockout mice still spent time awake, although their awake time and episode duration decreased during the dark period. This contradicts the claim that orexin is necessary for wakefulness. The paper also does not establish that activating orexin neurons is sufficient to produce wakefulness; it concludes that orexin helps regulate sleep–wake states. (LLM, conf=0.87)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [41] source

  • May combine two claims.

    Premisecitation

    In another study, significantly more orexin was observed in injured animals compared to sham-injured animals at 6 h post-injury, but not at 12 or 24 h.

    “They observed significantly more orexin in injured animals compared to sham-injured animals at 6 h post-injury, but not at 12 or 24 h.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [76] source

      The Animal model section defines the comparison groups as uninjured controls, rats with TBI but no stimulation, and rats with TBI given median nerve stimulation—not injured versus sham-injured animals. The ELISA results report significant differences in orexin-A among these groups at both 6 and 12 hours, but not at 24 hours, contrary to the claimed 6-hour-only result. Page numbers are unavailable in our copy. (LLM, conf=0.88)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Interpretationcitation

    In one study, there is both an increase in neuropeptide after injury and a decrease in orexin receptor levels, meaning the two may not correspond with one another.

    “In this particular study, there is both an increase in neuropeptide after injury and a decrease in orexin receptor levels, meaning that the two may not correspond with one another.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [78] source

      The Results section (“LIFUS increased the expression of OX-A and OXR1”; page unavailable) reports the opposite directions after injury: neuropeptide OX-A was lower in the TBI group than in the sham group, while orexin receptor 1 (OXR1) was higher. The Discussion also says OX-A decreased and OXR1 increased after TBI. Although the two levels moved in different directions, the claim reverses both changes. (LLM, conf=0.94)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    One study found no differences by sex with regard to orexin neurons themselves but did find differences in sleep parameters after injury.

    “One study found no differences by sex with regard to orexin neurons themselves but did find differences in sleep parameters after injury.71”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [71] source

      The Results section reports that female TBI mice had 16% more orexin-positive neurons than male TBI mice, contrary to the claim of no sex difference in those neurons. The Discussion does support the other part of the sentence: post-traumatic sleep percentage differed between male and female TBI mice during the first dark and second light cycles. (LLM, conf=0.88)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Orexin maintains wakefulness and arousal and regulates sleep stability.

    “orexin maintains wakefulness and arousal, as well as regulates sleep stability.17–21”
    Quote in the paperSubstantial claim3 of 5 sources checked
    • cites [17] source
    • cites [18] source
    • cites [19] source
    • cites [20] source
    • cites [21] source

  • May combine two claims.

    Premisecitation

    Sleep disruption is a symptom of TBI that can affect other known outcomes of injury.

    “Sleep disruption is a symptom of TBI that can affect other known outcomes of injury because a lack of proper sleep disrupts healthy living.10–15”
    Quote in the paperSubstantial claim2 of 6 sources checked
    • cites [10] Colten HR, 2006
    • cites [11] source

      The Discussion (page unavailable) reports that disrupted sleep continuity reduced positive mood in healthy adults, supporting the general point that poor sleep can affect well-being. The paper does not identify sleep disruption as a symptom of TBI or examine whether it affects other outcomes of brain injury. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
    • cites [12] source
    • cites [13] source

      The Short-term health consequences section (page unavailable) reports that sleep disruption can affect mood, cognition, memory, and performance, supporting the general point that poor sleep can affect health-related outcomes. But the paper does not identify sleep disruption as a symptom of TBI or establish its effects on outcomes specifically following TBI; searches for TBI and traumatic brain injury found no such passage. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [14] source
    • cites [15] source

  • May combine two claims.

    Premisecitation

    Without orexin or with altered orexin receptors, humans and animals experience narcolepsy.

    “Without orexin or with altered orexin receptors, humans and animals experience narcolepsy,34–39”
    Quote in the paperSubstantial claim3 of 6 sources checked
    • cites [34] source

      The Background and Discussion (page not given) link human narcolepsy to loss of hypocretin (orexin) and its neurons. The paper does not report narcolepsy in animals caused by orexin loss or altered orexin receptors, so those parts of the claim are not supported by this source. (LLM, conf=0.87)

      Experimental — accuracy not yet measured
    • cites [35] source
    • cites [36] source
    • cites [37] source
    • cites [38] source
    • cites [39] source

  • May combine two claims.

    Premisecitation

    Patients with mild TBI still experience sleep disorders and show decreased orexin in the CSF.

    “Patients with mild TBI still experience sleep disorders,59,60 and show decreased orexin in the CSF,56,57”
    Quote in the paperSubstantial claim1 of 4 sources checked
    • cites [59] source
    • cites [60] source
    • cites [56] source
    • cites [57] source

      The sleep-studies section (Table 2, page not provided) documents sleep disturbances six months after mild TBI, including objective excessive daytime sleepiness in 9 of 26 patients. The Conclusion reports low CSF hypocretin-1 (orexin) in most patients during acute TBI, but the clinical-characteristics section says levels were normal in 17 of 21 patients tested six months later. The paper therefore does not establish persistently decreased CSF orexin in patients with mild TBI as a group. (LLM, conf=0.85)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Some animal studies report a disordered sleep phenotype of increased wakefulness, more latency to sleep, or insomnia, which are also phenotypes of sleep disorders in human TBI patients.

    “Some studies report a disordered sleep phenotype of increased wakefulness, more latency to sleep, or insomnia in animals,65,70–72 which are also phenotypes of sleep disorders in human TBI patients.”
    Quote in the paperNot a substantial claim2 of 4 sources checked
    • cites [65] source
    • cites [70] source

      The Results report that brain-injured mice slept significantly less than shams during part of the light cycle, supporting increased wakefulness under that condition. The Discussion also describes fragmented sleep and clinical parallels, but does not report increased sleep latency or insomnia in these mice or establish that their increased wakefulness matches a human TBI phenotype. Page numbers are unavailable in our copy. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [71] source

      The Results report that female TBI mice slept 17% less than sham mice during the second light cycle, consistent with increased wakefulness in that group and period. The Discussion notes sleep disruption in human TBI patients, but the paper does not establish increased sleep latency or insomnia in its mice, or specifically identify those phenotypes in human TBI patients. Pages were not provided in our copy. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
    • cites [72] source

  • May combine two claims.

    Premisecitation

    Orexin knockout animals demonstrate the same amount of sleep overall compared to normal animals but have shorter bouts of sleep with more transitions between behavioral states.

    “Orexin knockout animals demonstrate the same amount of sleep overall compared to normal animals but have shorter bouts of sleep with more transitions between behavioral states.39–41”
    Quote in the paperNot a substantial claim2 of 3 sources checked
    • cites [39] source

      The sleep/wake analysis (indexed as Abstract; page unavailable) reports shorter non-REM sleep bouts and more frequent waking and non-REM episodes in orexin-null mice than in wild-type controls. It does not establish that their total sleep time was the same; it reports only nonsignificant changes in dark-phase non-REM sleep and a significant increase in dark-phase REM sleep. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [40] source

      The Results (page unavailable) describe more fragmented non-REM sleep and more rapid cycling between sleep and wakefulness in knockout mice during the dark phase. They do not establish equal overall sleep: knockout mice spent more time in REM sleep during the dark phase, and their REM episodes were longer, not shorter. The reported shorter episodes were episodes of wakefulness. (LLM, conf=0.87)

      Experimental — accuracy not yet measured
    • cites [41] source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Women accumulate sleep debt more rapidly than men do and might need more sleep to be functional.

    “It has been observed that women accumulate sleep debt more rapidly than men do and might need more sleep to be functional.96–98”
    Quote in the paperNot a substantial claim2 of 3 sources checked
    • cites [96] source

      In THEORETICAL IMPLICATIONS (page unavailable), the review reports a stronger slow-wave activity response in women than men after 40 hours of sleep deprivation. That supports a sex difference in response to sleep loss, but does not establish that women accumulate sleep debt faster or need more sleep to function. (LLM, conf=0.81)

      Experimental — accuracy not yet measured
    • cites [97] source

      The section “Sex differences in homeostatic response to sleep loss” says emerging evidence suggests sleep debt accumulates more quickly in women and may be more debilitating. But “Future Directions” asks whether women’s sleep needs differ from men’s; it does not establish that women need more sleep to function. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [98] source

  • May combine two claims.

    Premisecitation

    There is more of the precursor mRNA to orexin, prepro-orexin, in female animals, and higher levels of orexin in females.

    “There is more of the precursor mRNA to orexin, prepro-orexin, in female animals,108 and higher levels of orexin in females.109”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [108] source
    • cites [109] source

  • May combine two claims.

    Premisecitation

    In one study, orexin expression increased in general from 6 to 24 h after injury, with the highest observed expression at 12 h.

    “One study,79 found that orexin expression increased in general from 6 to 24 h after injury, though the highest orexin observed expression in their study was at 12 h after injury.”
    Quote in the paperNot a substantial claim1 of 1 sources checked

  • May combine two claims.

    Premisecitation

    With regards to sleep after TBI, women often report having worse sleep outcomes after injury than men, and the female sex is considered to be a risk factor when measuring sleep disorders after injury.

    “With regards to sleep after TBI, women often report having worse sleep outcomes after injury than men, and the female sex is considered to be a risk factor when measuring sleep disorders after injury.103–107”
    Quote in the paperNot a substantial claim2 of 5 sources checked
    • cites [103] source
    • cites [104] source
    • cites [105] source

      The Discussion reports a greater increase in sleep disturbances after TBI among older women (12.1%) than older men (5.0%), and the Conclusion says TBI has a greater impact on sleep disturbances in older women. The claim extends this finding beyond older adults and describes it as a risk factor for sleep disorders, whereas this study measured reported sleep disturbances. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
    • cites [106] source

      The Discussion reports that women had significant self-reported sleep disturbance after a single concussion, whereas men might not report it until after repeated concussions. It also recommends attention to gender when assessing post-concussion symptoms. The study concerns concussion and self-reported sleep disturbance; it does not establish female sex as a risk factor for diagnosed sleep disorders after TBI generally (page unavailable in our copy). (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [107] source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    While women normally have longer and better sleep, they also report a higher incidence of sleep disorders.

    “Interestingly, while women normally have longer and better sleep, they also report a higher incidence of sleep disorders.99–102”
    Quote in the paperNot a substantial claim2 of 4 sources checked
    • cites [99] source

      The Sleeping at Night section reports that 47.8% of female patients presenting with sleep-related problems often had trouble sleeping, compared with 26.7% of male patients. This supports a sex difference in reported symptoms within the clinical sample, but the paper does not establish a higher incidence of sleep disorders among women generally or say that women normally have longer and better sleep. (LLM, conf=0.87)

      Experimental — accuracy not yet measured
    • cites [100] source

      The Objective Measures section reports better objective sleep indicators in women, while Subjective Measures and Sleep Disorders reports more frequent complaints and higher risks of insomnia and restless leg syndrome. The paper does not establish that women generally sleep longer than men, and it cautions that better objective indicators may not mean women experience better sleep. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [101] source
    • cites [102] source

  • Classified as probably not a substantial claim.

    Premisecitation

    There is considerable evidence that sex is an important factor to consider in neuroscience research.

    “Finally, there is considerable evidence that sex is an important factor to consider in neuroscience research,92–95”
    Quote in the paperSubstantial claim3 of 4 sources checked
    • cites [92] source
    • cites [93] source
    • cites [94] source
    • cites [95] source

  • May combine two claims.

    Findingcitation

    In the authors' study, orexin was measured over time and only decreased expression after injury was seen, but all measurements were taken after 24 h post-injury.

    “In our study,49 we measured orexin over time and only saw decreased expression after injury, but all of our measurements were taken after 24 h post-injury.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [49] source

      The ‘Effect of TBI on orexin dynamics’ section reports lower extracellular orexin levels after injury. But the ‘Experimental overview’ says sampling resumed following injury and continued for 72 hours, not that all measurements were taken after 24 hours. The paper also reports increased orexin-positive cell counts, so ‘only decreased expression’ does not describe all its orexin findings. Page numbers were unavailable in our copy. (LLM, conf=0.91)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingown data

    Injured animals had a smaller percentage of orexin neurons stained with cFos, indicating less active orexin neurons after injury.

    “we found that injured animals had a smaller percentage of orexin neurons stained with cFos indicating less active orexin neurons after injury.”
    Quote in the paperSubstantial claim1 of 1 sources checked

  • May combine two claims.

    Premisecitation

    Another study found that male and female animals had differences in orexin neuron physiology after injury and that inhibitory activity might be more prominent in orexin neurons in females after injury.

    “Another study found that male and female animals had differences in orexin neuron physiology after injury and that inhibitory activity might be more prominent in orexin neurons in females after injury.83”
    Quote in the paperNot a substantial claim1 of 1 sources checked

  • May combine two claims.

    Premisecitation

    Orexin is associated with memory processing, motivation, reward, and addiction, which have been described as behaviors that are affected by TBI.

    “Orexin is also associated with memory processing,113–116 motivation, reward,117 and addiction,118 which have been described as behaviors that are affected by TBI.9,119–123”
    Quote in the paperSubstantial claim4 of 6 sources checked
    • cites [113] source
    • cites [114] source
    • cites [115] source
    • cites [116] source
    • cites [117] source
    • cites [118] source

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Findingnone given

    Reports of orexin and TBI do not typically comment on the feeding aspects of orexin neurons and there are no animal model studies that incorporate orexin, TBI, arousal, and feeding together.

    “However, reports of orexin and TBI do not typically comment on the feeding aspects of orexin neurons and there are no animal model studies that incorporate orexin, TBI, arousal, and feeding together.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.

  • May combine two claims. The quote only partly states this claim.

    Interpretationreasoning

    TBI affects the orexin/hypocretin system, including structural and functional changes to orexin neurons after injury.

    “Studies of TBI in human and animal subjects have shown that TBI affects the orexin system.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    A severe enough injury may damage all neurons regardless of sensitivity to injury.

    “a severe enough injury may damage all neurons regardless of sensitivity to injury.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductreasoning

    Human studies that measure orexin neuron number after TBI are measured after severe TBI and cannot determine what happens immediately after mild or moderate TBI.

    “A caveat of any studies that measure the number of orexin neurons in humans is that they are measured after severe TBI. These studies are unable to determine what happens to orexin neurons immediately following a mild or moderate TBI.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The result about orexin neuronal fibers being more present in the area surrounding the injury is qualitative and not quantitative.

    “Once again, this result is qualitative and not quantitative”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Another study reports that orexin receptors peak at 24 h post-injury and decrease after, though only qualitative findings are shown.

    “Another study,89 also follows this trend and reports that orexin receptors peak at 24 h post-injury and decrease after, though this study only shows qualitative, not quantitative findings.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [89] source

  • May combine two claims.

    Interpretationreasoning

    Studies that found an increase in orexin neuropeptide conducted measurements between 6 and 24 h post-injury, whereas studies that found decreases conducted measurements 24 h or longer after injury.

    “The studies that found an increase in orexin neuropeptide conducted their measurements between 6 and 24 h post-injury. The studies that found decreases in orexin neuropeptide conducted their measurements 24 h or longer after the injury.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    There may be an initial increase of orexin neuropeptide after injury and then a decrease.

    “This could be an indication that there is an initial increase of orexin neuropeptide after an injury and then a decrease.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Orexin expression is dependent on circadian rhythm, and timing is an important consideration when interpreting results from studies of orexin.

  • May combine two claims.

    Premisecitation

    At 7 days after injury, orexin receptor expression was observed in microglia and neurons, but not in astrocytes.

    “At 7 days after injury, orexin receptor expression was observed in microglia and neurons, but not in astrocytes.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Mihara et al. 2011 source
    • cites [89] source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductreasoning

    One published article does have a finding related to orexin and TBI, Kousi et al. 2021, but the authors did not think there was sufficient control subject data presented in this work and did not include this study in Table 1.

    “One published article does have a finding related to orexin and TBI, Kousi et al. 2021, but the authors did not think there was sufficient control subject data presented in this work and did not include this study in Table 1.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Kousi et al. 2021 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given

    The methods and models vary between each TBI study which contributes to the range of outcomes observed.

    “As with any group of TBI studies, the methods and models vary between each study which contributes to the range of outcomes observed.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationreasoning

    Differences in the ways that injuries are conducted, timing, and how results are gathered and interpreted undoubtedly contribute to differences in the data presented here.

    “Differences in the ways that injuries are conducted, timing, and how results are gathered and interpreted undoubtedly contribute to differences in the data presented here.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    The authors acknowledge that Kousi et al. 2021 is within the scope of this review even if the results are not presented in the table due to the lack of control subjects.

    “The authors do acknowledge that this study is within the scope of this review even if the results are not presented in the table of the lack of control subjects.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Kousi et al. 2021 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    This review was not preregistered.

    “This review was not preregistered.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    Orexin receptors are affected after TBI, a sign that after TBI, there may be a change in how the whole brain responds to orexin activity.

    “We have also discussed how orexin receptors are affected, a sign that after TBI, there may be a change in how the whole brain responds to orexin activity.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductreasoning

    The review presented is a narrative review, the authors did not use a formalized search strategy such as that used in a systematic review and thus formalized search strategies are not presented within the article.

    “The review presented is a narrative review, the authors did not use a formalized search strategy such as that used in a systematic review and thus formalized search strategies are not presented within the article.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The disruption of the orexin system after TBI includes changes in the number of orexin neurons and in how individual orexin neurons behave in synaptic circuits.

    “This includes the gross level of the number of neurons, as well as the functional level of how individual orexin neurons behave in synaptic circuits.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.
37 of 37

  • The paper relies on this without support.

    Orexin expression is dependent on circadian rhythm, and timing is an important consideration when interpreting results from studies of orexin.

    “Orexin expression is dependent on circadian rhythm and timing is an important consideration when interpreting results from studies of orexin.”

  • The paper relies on this without support.

    The field of orexin/hypocretin and TBI is limited enough that a narrative review would cover the field sufficiently.

    “The field of orexin/hypocretin and TBI is limited, and the authors felt a narrative review would cover the field sufficiently.”
2 of 2

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Huang study's orexin and receptor changes are reversed

    Major

    The narrative says this study found increased neuropeptide and decreased receptor levels. Table 1 reports decreased orexin content and increased receptor content.

  • Six-month patient count does not match the sex counts

    Minor

    The reported 53 men and 12 women total 65 patients, not 76.

    Reported 76 · recomputed 65

  • Conflicting counts for low orexin in the Ripley study

    Minor

    The narrative reports six of seven trauma patients with low orexin, while Table 1 reports five of six for the same study.

3 of 3

Cites

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Cited by

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Related

Authors
Somach, R. T., Lim, M. M., & Cohen, A. S.
Affiliations
  • Hospital of the University of Pennsylvania (US)
  • Oregon Health & Science University (US)
  • Children's Hospital of Philadelphia (US)
Corresponding author
Cohen, Akiva S.
ORCID
Venue
Neurotrauma Reports
Publisher
SAGE Publications
Published
2025-01-01
Volume
6
Issue
1
Pages
322-335
ISSN
2689-288X (ISSN-L)
DOI
10.1089/neur.2024.0111
PMC
PMC12040569
OpenAlex
W4409648219
Semantic Scholar
971ea306e874a4443e11733650b2fb723a40f5ae
Cited by
2
References
126
Citations by year
2026: 1 · 2025: 1
FWCI
1.14
Type
journal article
Language
en
Open access
Licence
Locations
  • Neurotrauma Reports (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (submittedVersion, cc-by)
  • PubMed Central (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • U.S. Department of Veterans Affairs (IK2 BX002712)
  • National Institute on Aging (P30 AG066518)
  • National Institute of Neurological Disorders and Stroke (R01 NS120099)
Topics
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Sleep and Wakefulness Research
  • Health Sciences › Medicine › Neurology › Traumatic Brain Injury and Neurovascular Disturbances
  • Health Sciences › Medicine › Epidemiology › Traumatic Brain Injury Research
Keywords
traumatic brain injury, orexin, sleep disruption, wakefulness, arousal, narcolepsy, orexin receptors, sex differences

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-14.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-14.

Cited sources are checked by gpt-6-sol.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

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