A brainstem-to-mediodorsal thalamic pathway mediates sound-induced arousal from slow-wave sleep

Thalamic Stroke and Sleep Study: Sleep-Wake, Autonomic Regulation, and Cognition

BACKGROUND

Thalamic stroke (TS) often presents with complex clinical manifestations, including sleep-wake disturbances, cognitive deficits, and autonomic dysregulation, yet the interaction between these functional alterations remains poorly understood. We aimed to investigate these interactions in a case-control lesion study.

METHODS

Patients with acute TS and no-stroke controls were included prospectively in this study. The data were collected from June 2020 to September 2022 at the stroke unit or sleep laboratory of the Inselspital (Bern). Sleep-wake variables (questionnaires, actigraphy, polysomnography including electroencephalography-based sleep macroarchitecture and microarchitecture, and analysis of electroencephalography spectral power), nocturnal heart rate variability, and cognition (5 tests: processing speed, attention, working memory, visual memory, and verbal memory) were assessed at study inclusion (within 5 days poststroke for patients with stroke).

RESULTS

Data from 16 patients with TS and 32 control volunteers were analyzed. All patients with stroke had lesions of the ventral nuclei, while 9 of 16 patients with stroke also had lesions in the mediodorsal nucleus (1 bilateral). TS was characterized by long sleep duration and high nocturnal heart rate variability with parasympathetic dominance. The alterations in sleep electroencephalography included a decrease in cyclic alternating pattern index, slow spindle density, the quantity of isolated sawtooth wave segments, and electroencephalography spectral power predominantly affecting the alpha band. The mediodorsal lesions were associated with a decrease in sleep spindle amplitude and slow wave amplitude and with an increase in phasic rapid eye movement sleep. Furthermore, patients with TS had deficits in processing speed, working memory, and verbal memory, mostly pronounced in patients with mediodorsal lesions. In a combined data set, multiple correlations were observed between sleep-wake, autonomic, and cognitive parameters, many of which depended on the presence of a TS.

CONCLUSIONS

These findings emphasize the role of the thalamus in the regulation of sleep-wake, autonomic, and cognitive functions and their interactions and provide the theoretical basis for the therapies targeting the thalamus.

Shared subcortical arousal systems across sensory modalities during transient modulation of attention

Subcortical arousal systems are known to play a key role in controlling sustained changes in attention and conscious awareness. Recent studies indicate that these systems have a major influence on short-term dynamic modulation of visual attention, but their role across sensory modalities is not fully understood. In this study, we investigated shared subcortical arousal systems across sensory modalities during transient changes in attention using block and event-related fMRI paradigms. We analyzed massive publicly available fMRI datasets collected while 1561 participants performed visual, auditory, tactile, and taste perception tasks. Our analyses revealed a shared circuit of subcortical arousal systems exhibiting early transient increases in activity in midbrain reticular formation and central thalamus across perceptual modalities, as well as less consistent increases in pons, hypothalamus, basal forebrain, and basal ganglia. Identifying these networks is critical for understanding mechanisms of normal attention and consciousness and may help facilitate subcortical targeting for therapeutic neuromodulation.

Neural circuit underlying individual differences in visual escape habituation

Emotions like fear help organisms respond to threats. Repeated predator exposure leads to adaptive responses with unclear neural mechanisms behind individual variability. We identify two escape behaviors in mice-persistent escape (T1) and rapid habituation (T2)-linked to unique arousal states under repetitive looming stimuli. Combining multichannel recording, circuit mapping, optogenetics, and behavioral analyses, we find parallel pathways from the superior colliculus (SC) to the basolateral amygdala (BLA) via the ventral tegmental area (VTA) for T1 and via the mediodorsal thalamus (MD) for T2. T1 involves heightened arousal, while T2 features rapid habituation. The MD integrates SC and insular cortex inputs to modulate arousal and defensive behaviors. This work reveals neural circuits underpinning adaptive threat responses and individual variability.

Neural Processing of Taste-Related Signals in the Mediodorsal Thalamus of Mice

Our consummatory decisions depend on the taste of food and the reward experienced while eating, which are processed through neural computations in interconnected brain areas. Although many gustatory regions of rodents have been explored, the mediodorsal nucleus of the thalamus (MD) remains understudied. The MD, a multimodal brain area connected with gustatory centers, is often studied for its role in processing associative and cognitive information and has been shown to represent intraorally delivered chemosensory stimuli after strong retronasal odor-taste associations. Key questions remain about whether MD neurons can process taste quality independently of odor-taste associations and how they represent extraoral signals predicting rewarding and aversive gustatory outcomes. Here, using C57 male and female mice we present electrophysiological evidence demonstrating how MD neurons represent and encode 1) the identity and concentrations of basic taste qualities during active licking, and 2) auditory signals anticipating rewarding and aversive taste outcomes. Our data reveal that MD neurons can reliably and dynamically encode taste identity in a broadly tuned manner and taste concentrations with spiking activity positively and negatively correlated with stimulus intensity. Our data also show that MD can represent information related to predictive cues and their associated outcomes, regardless of whether the cue predicts a rewarding or aversive outcome. In summary, our findings suggest that the mediodorsal thalamus is integral to the taste pathway, as it can encode sensory-discriminative dimensions of tastants and participate in processing associative information essential for ingestive behaviors.Significance Statement Dietary decisions are driven by the taste of the food and the reward experienced while eating. This information is processed through neural computations across interconnected brain areas. Given its neural connections, the mediodorsal thalamus (MD) could be part of this network. However, its involvement in gustatory processing is largely ignored. This study examines how MD neurons respond to taste quality, intensity, and expectation by analyzing the electrical activity of MD neurons in mice allowed to freely lick a spout to obtain different tastes. Our findings support the idea that the MD is part of the brain network responsible for processing sensory and associative information relevant to eating.

Temporal Association Cortex Gates Sound-Evoked Arousal from NREM Sleep

Sound-evoked wakefulness from sleep is crucial in daily life, yet its neural mechanisms remain poorly understood. It is found that CaMKIIα+ neurons in the temporal association cortex (TeA) of mice are not essential for natural awakening from sleep. However, optogenetic activation of these neurons reliably induces wakefulness from non-rapid eye movement (NREM) sleep but not from rapid eye movement (REM) sleep. In vivo electrophysiological and calcium recordings further demonstrated that TeA neurons are monotonically tuned to sound intensity but not frequency. More importantly, it is found that the activity of CaMKIIα+ neurons in TeA can gate sound-evoked arousal from NREM sleep, which is further confirmed by optogenetic manipulations. Further investigation reveals that the baseline excitability of TeA CaMKIIα+ neurons and the delta oscillations in the electroencephalogram are particularly important in regulating the evoked activity of TeA neurons. Anatomical and functional screening of downstream targets of TeA reveals that excitatory projections from TeA glutamatergic neurons to glutamatergic neurons in the basolateral/lateral amygdala are critical for modulating sound-evoked arousal from NREM sleep. These findings uncover a top-down regulatory circuit that selectively governs sound-evoked arousal from NREM sleep, with the TeA functioning as a key connecting cortex to subcortical regions.

Genetic and functional adaptations and alcohol-biased signaling in the mediodorsal thalamus of alcohol dependent mice

Alcohol Use Disorder (AUD) is a significant health concern characterized by an individual's inability to control alcohol intake. With alcohol misuse increasing and abstinence rates declining, leading to severe social and health consequences, it is crucial to uncover effective treatment strategies for AUD by focusing on understanding neuroadaptations and cellular mechanisms. The mediodorsal thalamus (MD) is a brain region essential for cognitive functioning and reward-guided choices. However, the effects of alcohol (ethanol) dependence on MD neuroadaptations and how dependence alters MD activity during choice behaviors for alcohol and a natural reward (sucrose) are not well understood. Adult C57BL/6J mice treated with chronic intermittent ethanol (CIE) exposure were used to assess genetic and functional adaptations in the MD. Fiber photometry-based recordings of GCaMP6f expressed in the MD of C57BL/6J mice were acquired to investigate in vivo neural adaptations during choice drinking sessions for alcohol (15%) and either water or sucrose (3%). There were time-dependent changes in cFos and transcript expression during acute withdrawal and early abstinence. Differentially expressed genes were identified in control mice across different circadian time points and when comparing control and alcohol dependent mice. Gene Ontology enrichment analysis of the alcohol-sensitive genes revealed disruption of genes that control glial function, axonal myelination, and protein binding. CIE exposure also increased evoked firing in MD cells at 72 hours of withdrawal. In alcohol-dependent male and female mice that show increased alcohol drinking and preference for alcohol over water, we observed an increase in alcohol intake and preference for alcohol when mice were given a choice between alcohol and sucrose. Fiber photometry recordings demonstrated that MD activity is elevated during and after licking bouts for alcohol, water, and sucrose, and the signal for alcohol is significantly higher than that for water or sucrose during drinking. The elevated signal during alcohol bouts persisted in alcohol dependent mice. These findings demonstrate that CIE causes genetic and functional neuroadaptations in the MD and that alcohol dependence enhances alcohol-biased behaviors, with the MD uniquely responsive to alcohol, even in dependent mice.

A distributed auditory network mediated by pontine central gray underlies ultra-fast awakening in response to alerting sounds

Sleeping animals can be woken up rapidly by external threat signals, which is an essential defense mechanism for survival. However, neuronal circuits underlying the fast transmission of sensory signals for this process remain unclear. Here, we report in mice that alerting sound can induce rapid awakening within hundreds of milliseconds and that glutamatergic neurons in the pontine central gray (PCG) play an important role in this process. These neurons exhibit higher sensitivity to auditory stimuli in sleep than wakefulness. Suppressing these neurons results in reduced sound-induced awakening and increased sleep in intrinsic sleep/wake cycles, whereas their activation induces ultra-fast awakening from sleep and accelerates awakening from anesthesia. Additionally, the sound-induced awakening can be attributed to the propagation of auditory signals from the PCG to multiple arousal-related regions, including the mediodorsal thalamus, lateral hypothalamus, and ventral tegmental area. Thus, the PCG serves as an essential distribution center to orchestrate a global auditory network to promote rapid awakening.

Auditory circuits: Watchmen of the sleeping brain

A new study shows that glutamatergic neurons of the pontine central gray (PCG) play a key role in mediating rapid sound-induced awakenings from sleep by relaying short-latency auditory information to multiple arousal centers in the brain.

Shared subcortical arousal systems across sensory modalities during transient modulation of attention

Subcortical arousal systems are known to play a key role in controlling sustained changes in attention and conscious awareness. Recent studies indicate that these systems have a major influence on short-term dynamic modulation of visual attention, but their role across sensory modalities is not fully understood. In this study, we investigated shared subcortical arousal systems across sensory modalities during transient changes in attention using block and event-related fMRI paradigms. We analyzed massive publicly available fMRI datasets collected while 1,561 participants performed visual, auditory, tactile, and taste perception tasks. Our analyses revealed a shared circuit of subcortical arousal systems exhibiting early transient increases in activity in midbrain reticular formation and central thalamus across perceptual modalities, as well as less consistent increases in pons, hypothalamus, basal forebrain, and basal ganglia. Identifying these networks is critical for understanding mechanisms of normal attention and consciousness and may help facilitate subcortical targeting for therapeutic neuromodulation.

Neurotensin-specific corticothalamic circuit regulates innate response conflict

Animals must simultaneously select and balance multiple action contingencies in ambiguous situations: for instance, evading danger during feeding. This has rarely been examined in the context of information selection; despite corticothalamic pathways that mediate sensory attention being relatively well characterized, neural mechanisms filtering conflicting actions remain unclear. Here, we develop a new loom/feed test to observe conflict between naturally induced fear and feeding and identify a novel anterior cingulate cortex (ACC) output to the ventral anterior and ventral lateral thalamus (VA/VL) that adjusts selectivity between these innate actions. Using micro-endoscopy and fiber photometry, we reveal that activity in corticofugal outputs was lowered during unbalanced/singularly occupied periods, as were the resulting decreased thalamic initiation-related signals for less-favored actions, suggesting that the integration of ACC-thalamic firing may directly regulate the output of behavior choices. Accordingly, the optoinhibition of ACC-VA/VL circuits induced high bias toward feeding at the expense of defense. To identify upstream "commander" cortical cells gating this output, we established dual-order tracing (DOT)-translating ribosome affinity purification (TRAP)-a scheme to label upstream neurons with transcriptome analysis-and found a novel population of neurotensin-positive interneurons (ACCNts). The photoexcitation of ACCNts cells indeed caused similarly hyper-selective behaviors. Collectively, this new "corticofugal action filter" scheme suggests that communication in multi-step cingulate circuits may critically influence the summation of motor signals in thalamic outputs, regulating bias between innate action types.

Protocol for in vivo dual-color fiber photometry in the mouse thalamus

In vivo calcium imaging of neural activity is an indispensable approach for understanding the mechanisms and functions of neural system. Development of advanced imaging tools and various genetically encoded calcium indicators allows us to simultaneously record the activity of different neural populations. Here, we present a protocol for acquiring neural activity of two discrete neural populations in mice using dual-color fiber photometry. We describe steps for injecting viral constructs and implanting the fiber optic through stereotaxic surgery, calcium signal acquisition, and data analysis. We also describe the incorporation of electroencephalogram and electromyography recordings with dual-color fiber photometry analysis. For complete details on the use and execution of this protocol, please refer to Shin et al.1.

Dynamic modulation of mouse thalamocortical visual activity by salient sounds

Visual responses of the primary visual cortex (V1) are altered by sound. Sound-driven behavioral arousal suggests that, in addition to direct inputs from the primary auditory cortex (A1), multiple other sources may shape V1 responses to sound. Here, we show in anesthetized mice that sound (white noise, ≥70dB) drives a biphasic modulation of V1 visually driven gamma-band activity, comprising fast-transient inhibitory and slow, prolonged excitatory (A1-independent) arousal-driven components. An analogous yet quicker modulation of the visual response also occurred earlier in the visual pathway, at the level of the dorsolateral geniculate nucleus (dLGN), where sound transiently inhibited the early phasic visual response and subsequently induced a prolonged increase in tonic spiking activity and gamma rhythmicity. Our results demonstrate that sound-driven modulations of visual activity are not exclusive to V1 and suggest that thalamocortical inputs from the dLGN to V1 contribute to shaping V1 visual response to sound.

A genome-wide association study reveals the relationship between human genetic variation and the nasal microbiome

The nasal cavity harbors diverse microbiota that contributes to human health and respiratory diseases. However, whether and to what extent the host genome shapes the nasal microbiome remains largely unknown. Here, by dissecting the human genome and nasal metagenome data from 1401 healthy individuals, we demonstrated that the top three host genetic principal components strongly correlated with the nasal microbiota diversity and composition. The genetic association analyses identified 63 genome-wide significant loci affecting the nasal microbial taxa and functions, of which 2 loci reached study-wide significance (p < 1.7 × 10-10): rs73268759 within CAMK2A associated with genus Actinomyces and family Actinomycetaceae; and rs35211877 near POM121L12 with Gemella asaccharolytica. In addition to respiratory-related diseases, the associated loci are mainly implicated in cardiometabolic or neuropsychiatric diseases. Functional analysis showed the associated genes were most significantly expressed in the nasal airway epithelium tissue and enriched in the calcium signaling and hippo signaling pathway. Further observational correlation and Mendelian randomization analyses consistently suggested the causal effects of Serratia grimesii and Yokenella regensburgei on cardiometabolic biomarkers (cystine, glutamic acid, and creatine). This study suggested that the host genome plays an important role in shaping the nasal microbiome.