Activation of locus coeruleus noradrenergic neurons rapidly drives homeostatic sleep pressure.

Homeostatic sleep regulation is essential for optimizing the amount and timing of sleep, but the underlying mechanism remains unclear. Optogenetic activation of locus coeruleus noradrenergic neurons immediately increased sleep propensity following transient wakefulness. Fiber photometry showed that repeated optogenetic or sensory stimulation caused rapid declines of locus coeruleus calcium activity and noradrenaline release. This suggests that functional fatigue of noradrenergic neurons, which reduces their wake-promoting capacity, contributes to sleep pressure.

Circuit mechanism for suppression of frontal cortical ignition during NREM sleep.

Conscious perception is greatly diminished during sleep, but the underlying circuit mechanism is poorly understood. We show that cortical ignition-a brain process shown to be associated with conscious awareness in humans and non-human primates-is strongly suppressed during non-rapid-eye-movement (NREM) sleep in mice due to reduced cholinergic modulation and rapid inhibition of cortical responses. Brain-wide functional ultrasound imaging and cell-type-specific calcium imaging combined with optogenetics showed that activity propagation from visual to frontal cortex is markedly reduced during NREM sleep due to strong inhibition of frontal pyramidal neurons. Chemogenetic activation and inactivation of basal forebrain cholinergic neurons powerfully increased and decreased visual-to-frontal activity propagation, respectively. Furthermore, although multiple subtypes of dendrite-targeting GABAergic interneurons in the frontal cortex are more active during wakefulness, soma-targeting parvalbumin-expressing interneurons are more active during sleep. Chemogenetic manipulation of parvalbumin interneurons showed that sleep/wake-dependent cortical ignition is strongly modulated by perisomatic inhibition of pyramidal neurons.

Cardiovascular baroreflex circuit moonlights in sleep control.

Sleep disturbances are strongly associated with cardiovascular diseases. Baroreflex, a basic cardiovascular regulation mechanism, is modulated by sleep-wake states. Here, we show that neurons at key stages of baroreflex pathways also promote sleep. Using activity-dependent genetic labeling, we tagged neurons in the nucleus of the solitary tract (NST) activated by blood pressure elevation and confirmed their barosensitivity with optrode recording and calcium imaging. Chemogenetic or optogenetic activation of these neurons promoted non-REM sleep in addition to decreasing blood pressure and heart rate. GABAergic neurons in the caudal ventrolateral medulla (CVLM)-a downstream target of the NST for vasomotor baroreflex-also promote non-REM sleep, partly by inhibiting the sympathoexcitatory and wake-promoting adrenergic neurons in the rostral ventrolateral medulla (RVLM). Cholinergic neurons in the nucleus ambiguous-a target of the NST for cardiac baroreflex-promoted non-REM sleep as well. Thus, key components of the cardiovascular baroreflex circuit are also integral to sleep-wake brain-state regulation.

Cannabinoids modulate associative cerebellar learning via alterations in behavioral state.

Cannabinoids are notorious and profound modulators of behavioral state. In the brain, endocannabinoids act via Type 1-cannabinoid receptors (CB1) to modulate synaptic transmission and mediate multiple forms of synaptic plasticity. CB1 knockout (CB1KO) mice display a range of behavioral phenotypes, in particular hypoactivity and various deficits in learning and memory, including cerebellum-dependent delay eyeblink conditioning. Here we find that the apparent effects of CB1 deletion on cerebellar learning are not due to direct effects on CB1-dependent plasticity, but rather, arise as a secondary consequence of altered behavioral state. Hypoactivity of CB1KO mice accounts for their impaired eyeblink conditioning across both animals and trials. Moreover, learning in these mutants is rescued by walking on a motorized treadmill during training. Finally, cerebellar granule-cell-specific CB1KOs exhibit normal eyeblink conditioning, and both global and granule-cell-specific CB1KOs display normal cerebellum-dependent locomotor coordination and learning. These findings highlight the modulation of behavioral state as a powerful independent means through which individual genes contribute to complex behaviors.

Shared and specific signatures of locomotor ataxia in mutant mice.

Several spontaneous mouse mutants with deficits in motor coordination and associated cerebellar neuropathology have been described. Intriguingly, both visible gait alterations and neuroanatomical abnormalities throughout the brain differ across mutants. We previously used the LocoMouse system to quantify specific deficits in locomotor coordination in mildly ataxic Purkinje cell degeneration mice (pcd; Machado et al., 2015). Here, we analyze the locomotor behavior of severely ataxic reeler mutants and compare and contrast it with that of pcd. Despite clearly visible gait differences, direct comparison of locomotor kinematics and linear discriminant analysis reveal a surprisingly similar pattern of impairments in multijoint, interlimb, and whole-body coordination in the two mutants. These findings capture both shared and specific signatures of gait ataxia and provide a quantitative foundation for mapping specific locomotor impairments onto distinct neuropathologies in mice.

Spatial and Temporal Locomotor Learning in Mouse Cerebellum.

Stable and efficient locomotion requires the precise coordination of movement across the limbs and body. Learned changes in interlimb coordination can be induced by exposure to a split-belt treadmill that imposes different speeds under each side of the body. Here, we demonstrate locomotor learning on a split-belt treadmill in mice. Mouse locomotor adaptation is specific to measures of interlimb coordination, has spatial and temporal components that adapt at different rates, and is context specific. The many similarities between human and mouse locomotor adaptation suggest that this form of locomotor learning is highly conserved across vertebrates. Using a variety of approaches, we demonstrate that split-belt adaptation in mice specifically depends on the intermediate cerebellum but is insensitive to large lesions of the cerebral cortex. Finally, cell-type-specific chemogenetics combined with quantitative behavioral analysis reveals that spatial and temporal components of locomotor adaptation are dissociable on the circuit level. VIDEO ABSTRACT.

A quantitative framework for whole-body coordination reveals specific deficits in freely walking ataxic mice.

The coordination of movement across the body is a fundamental, yet poorly understood aspect of motor control. Mutant mice with cerebellar circuit defects exhibit characteristic impairments in locomotor coordination; however, the fundamental features of this gait ataxia have not been effectively isolated. Here we describe a novel system (LocoMouse) for analyzing limb, head, and tail kinematics of freely walking mice. Analysis of visibly ataxic Purkinje cell degeneration (pcd) mice reveals that while differences in the forward motion of individual paws are fully accounted for by changes in walking speed and body size, more complex 3D trajectories and, especially, inter-limb and whole-body coordination are specifically impaired. Moreover, the coordination deficits in pcd are consistent with a failure to predict and compensate for the consequences of movement across the body. These results isolate specific impairments in whole-body coordination in mice and provide a quantitative framework for understanding cerebellar contributions to coordinated locomotion.

Attentional modulation of reward processing in the human brain.

Although neural signals of reward anticipation have been studied extensively, the functional relationship between reward and attention has remained unclear: Neural signals implicated in reward processing could either reflect attentional biases towards motivationally salient stimuli, or proceed independently of attentional processes. Here, we sought to disentangle reward and attention-related neural processes by independently modulating reward value and attentional task demands in a functional magnetic resonance imaging study in healthy human participants. During presentation of a visual reward cue that indicated whether monetary reward could be obtained in a subsequent reaction time task, participants either attended to the reward cue or performed an unrelated attention-demanding task at two different levels of difficulty. In ventral striatum and ventral tegmental area, neural responses were modulated by reward anticipation irrespective of attentional demands, thus indicating attention-independent processing of reward cues. By contrast, additive effects of reward and attention were observed in visual cortex. Critically, reward-related activations in right anterior insula strongly depended on attention to the reward cue. Dynamic causal modelling revealed that the attentional modulation of reward processing in insular cortex was mediated by enhanced effective connectivity from ventral striatum to anterior insula. Our results provide evidence for distinct functional roles of the brain regions involved in the processing of reward-indicating information: While subcortical structures signal the motivational salience of reward cues even when attention is fully engaged elsewhere, reward-related responses in anterior insula depend on available attentional resources, likely reflecting the conscious evaluation of sensory information with respect to motivational value.

Interaction of age and opioid dependence on length of hospital stay for spine surgery patients.

Clinical information suggests that opioid dependence is a major contributor to poor outcomes involving health status and to increased length of stay in hospital settings. Before spine surgery, 150 patients who were using an opioid medication for pain relief were interviewed using the six World Health Organization (WHO) guidelines for the diagnosis of opioid dependence. Three groups were defined: opioid-dependent, nonopioid-dependent, and a subclinical group. Results revealed an average of 20% of patients (N = 30) who met the WHO criteria for the diagnosis of opioid dependence. There were significant positive correlations between age and number of positive WHO criteria, length of stay, and time under surgery. Length of stay was significantly higher for the older age group (> 55 yr.). ANCOVA analysis using two opioid dependence groups (+ and -) and age group as independent variables affecting length of stay, after controlling for type of surgery, pain intensity, and number of previous spine surgeries, revealed that effects of opioid dependence status and age were significant but their interaction was not. Age did add length of stay independently of opioid dependence status; older adults remain in the hospital longer for various reasons probably associated with comorbidities.

Tolerance of stereopsis to conjunctive cyclorotation.

Stereopsis is largely unperturbed by various types of eye, head, and target movements. Here, we used a simple setup to investigate the limits of a previously untested type of stimulus motion on stereoscopic depth perception. Clockwise and counterclockwise rotations of an autostereogram were used to describe the limits of stereopsis to roll-tilt. The result showed intact depth perception with stimulus rotation up to approximately 12 degrees, regardless of rotation direction and viewing distance, indicating a tolerant mechanism for stereoscopic processing by the human neural system.

The fifth vital sign--what does it mean?

Acute pain is reported as a presenting symptom in over 80% of physician visits. Chronic pain affects an estimated 76.2 million Americans--more than diabetes, heart disease, and cancer combined. It has been estimated to be undertreated in up to 80% of patients in some settings. Pain costs the American public more than $100 billion each year in health care, compensation, and litigation. That's why pain was officially declared "The Fifth Vital Sign." Henceforth the evaluation of pain became a requirement of proper patient care as important and basic as the assessment and management of temperature, blood pressure, respiratory rate, and heart rate. The numeric pain scale certainly has a place in care and in pain management; however, it is important to assess the patient's communication and self-management style and to recognize that patients, like pain, are on a continuum with varied styles of communication and adaptation. It is easy to get lost in the process, even when the process is initiated with the best of intentions. In the quest for individualized medicine, it might be best to keep pain assessment in the individualization arena.