Somnotate: A probabilistic sleep stage classifier for studying vigilance state transitions.

Electrophysiological recordings from freely behaving animals are a widespread and powerful mode of investigation in sleep research. These recordings generate large amounts of data that require sleep stage annotation (polysomnography), in which the data is parcellated according to three vigilance states: awake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep. Manual and current computational annotation methods ignore intermediate states because the classification features become ambiguous, even though intermediate states contain important information regarding vigilance state dynamics. To address this problem, we have developed "Somnotate"-a probabilistic classifier based on a combination of linear discriminant analysis (LDA) with a hidden Markov model (HMM). First we demonstrate that Somnotate sets new standards in polysomnography, exhibiting annotation accuracies that exceed human experts on mouse electrophysiological data, remarkable robustness to errors in the training data, compatibility with different recording configurations, and an ability to maintain high accuracy during experimental interventions. However, the key feature of Somnotate is that it quantifies and reports the certainty of its annotations. We leverage this feature to reveal that many intermediate vigilance states cluster around state transitions, whereas others correspond to failed attempts to transition. This enables us to show for the first time that the success rates of different types of transition are differentially affected by experimental manipulations and can explain previously observed sleep patterns. Somnotate is open-source and has the potential to both facilitate the study of sleep stage transitions and offer new insights into the mechanisms underlying sleep-wake dynamics.

The hypothalamic link between arousal and sleep homeostasis in mice.

Sleep and wakefulness are not simple, homogenous all-or-none states but represent a spectrum of substates, distinguished by behavior, levels of arousal, and brain activity at the local and global levels. Until now, the role of the hypothalamic circuitry in sleep-wake control was studied primarily with respect to its contribution to rapid state transitions. In contrast, whether the hypothalamus modulates within-state dynamics (state "quality") and the functional significance thereof remains unexplored. Here, we show that photoactivation of inhibitory neurons in the lateral preoptic area (LPO) of the hypothalamus of adult male and female laboratory mice does not merely trigger awakening from sleep, but the resulting awake state is also characterized by an activated electroencephalogram (EEG) pattern, suggesting increased levels of arousal. This was associated with a faster build-up of sleep pressure, as reflected in higher EEG slow-wave activity (SWA) during subsequent sleep. In contrast, photoinhibition of inhibitory LPO neurons did not result in changes in vigilance states but was associated with persistently increased EEG SWA during spontaneous sleep. These findings suggest a role of the LPO in regulating arousal levels, which we propose as a key variable shaping the daily architecture of sleep-wake states.

Circadian Biology and Stroke.

Circadian biology modulates almost all aspects of mammalian physiology, disease, and response to therapies. Emerging data suggest that circadian biology may significantly affect the mechanisms of susceptibility, injury, recovery, and the response to therapy in stroke. In this review/perspective, we survey the accumulating literature and attempt to connect molecular, cellular, and physiological pathways in circadian biology to clinical consequences in stroke. Accounting for the complex and multifactorial effects of circadian rhythm may improve translational opportunities for stroke diagnostics and therapeutics.

Distinguishing psychogenic nonepileptic, mixed, and epileptic seizures using systemic measures and reported experiences.

OBJECTIVES: Our primary objective was to better discern features that can differentiate people with 'mixed' symptomatology from those who experience epileptic seizures (ES) or functional/psychogenic nonepileptic seizures (PNES) alone, in a population of patients referred for video-telemetry. We wished to see if we could establish the prevalence of PNES in this population of interest as well as compare both objective (e.g. videotelemetry reports and heart rate measurements) and subjective, patient-centered measures (reported symptoms and experiences). METHODS: Data were sourced from a database of all video-telemetry patients admitted to the John Radcliffe Hospital (Oxford, UK) between 1st Jan 2014 and 31st Jan 2016; video-electroencephalogram (vEEG) reports for the above patients; neurology clinic letters; multidisciplinary Team (MDT) reports; psychology assessments and patient notes for all vEEG patients referred for surgical work up. Mixed cases with a dual ES/PNES diagnosis were carefully evaluated again by the Consultant Neurologist under whose care each respective patient was, through case-by-case evaluation of EEG and telemetry reports. We compared mean heart rate during attacks captured on vEEG, number of physical symptoms reported, episode length, and postictal confusion between the three groups (ES; PNES; ES and PNES (mixed)). We evaluated the groups in terms of demographic and psychological parameters as well as prescription of anti-seizure medication. Pearson correlation significance was examined at 95% level of significance for p-values corrected for multiple comparisons. RESULTS: Overall, mixed cases reported experiencing a significantly lower number of physical symptoms compared to PNES cases (p = 0.018). The heart rate of PNES cases was significantly lower than that of mixed cases during the attacks (p = 0.003). ES patients exhibited the highest heart rate of all three groups and a greater degree of postictal confusion (adjusted p = 0.003 and p < 0.001, respectively) compared to those with PNES. There was no statistically significant difference in episode length between mixed and ES cases, while PNES patients had significantly longer episode duration (p = 0.021) compared to the mixed group. We noted that 81.6% of PNES patients were taking at least one anti-seizure medication. CONCLUSION: Patients with mixed seizures seem to be part of a spectrum between ES and PNES cases. Mixed cases are more similar to the ES group with regard to episode length and number of symptoms reported. In the PNES cohort, we found an over-reporting of ictal symptoms (e.g. palpitations, diaphoresis) disproportionate to recorded heart rate, which is lower in PNES than in epileptic attacks. This seems consistent with PNES cases experiencing a degree of impaired interoceptive processing, as part of a functional disorder spectrum. We noted that there was tendency for overmedication in the PNES group. The need for 'de-prescribing' should be addressed with measures that include better liaison with the community care team. With regard to potential autonomic dysregulation in the mixed cases, it might be interesting to see if vagus nerve stimulation could be accompanied by normalization of cardiovascular physiology parameters for people with both epileptic and psychogenic nonepileptic seizures.

An Assessment of Physical and N6-Cyclohexyladenosine-Induced Hypothermia in Rodent Distal Focal Ischemic Stroke.

Therapeutic hypothermia (TH) mitigates damage in ischemic stroke models. However, safer and easier TH methods (e.g., pharmacological) are needed to circumvent physical cooling complications. This study evaluated systemic and pharmacologically induced TH using the adenosine A1 receptor agonist, N6-cyclohexyladenosine (CHA), with control groups in male Sprague-Dawley rats. CHA was administered intraperitoneally 10 minutes following a 2-hour intraluminal middle cerebral artery occlusion. We used a 1.5 mg/kg induction dose, followed by three 1.0 mg/kg doses every 6 hours for a total of 4 doses, causing 20-24 hours of hypothermia. Animals assigned to physical hypothermia and CHA-hypothermia had similar induction rates and nadir temperatures, but forced cooling lasted ∼6 hours longer compared with CHA-treated animals. The divergence is likely attributable to individual differences in CHA metabolism, which led to varied durations at nadir, whereas physical hypothermia was better regulated. Physical hypothermia significantly reduced infarction (primary endpoint) on day 7 (mean reduction of 36.8 mm3 or 39% reduction; p = 0.021 vs. normothermic animals; Cohen's d = 0.75), whereas CHA-induced hypothermia did not (p = 0.33). Similarly, physical cooling improved neurological function (physical hypothermia median = 0, physical normothermia median = 2; p = 0.008) and CHA-induced cooling did not (p > 0.99). Our findings demonstrate that forced cooling was neuroprotective compared with controls, but prolonged CHA-induced cooling was not neuroprotective.

The relationship between fasting-induced torpor, sleep, and wakefulness in laboratory mice.

STUDY OBJECTIVES: Torpor is a regulated and reversible state of metabolic suppression used by many mammalian species to conserve energy. Whereas the relationship between torpor and sleep has been well-studied in seasonal hibernators, less is known about the effects of fasting-induced torpor on states of vigilance and brain activity in laboratory mice. METHODS: Continuous monitoring of electroencephalogram (EEG), electromyogram (EMG), and surface body temperature was undertaken in adult, male C57BL/6 mice over consecutive days of scheduled restricted feeding. RESULTS: All animals showed bouts of hypothermia that became progressively deeper and longer as fasting progressed. EEG and EMG were markedly affected by hypothermia, although the typical electrophysiological signatures of non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep, and wakefulness enabled us to perform vigilance-state classification in all cases. Consistent with previous studies, hypothermic bouts were initiated from a state indistinguishable from NREM sleep, with EEG power decreasing gradually in parallel with decreasing surface body temperature. During deep hypothermia, REM sleep was largely abolished, and we observed shivering-associated intense bursts of muscle activity. CONCLUSIONS: Our study highlights important similarities between EEG signatures of fasting-induced torpor in mice, daily torpor in Djungarian hamsters and hibernation in seasonally hibernating species. Future studies are necessary to clarify the effects on fasting-induced torpor on subsequent sleep.