Optogenetics publications

Stimulus-specific adaptation is a key feature of sensory systems, where the repeated presentation of a stimulus results in diminishing neuronal responses specifically to that stimulus, but not to a different stimulus. Cortical neurons display varying degrees of stimulus-specific adaptation, with cortical circuits shaping the dynamics of these responses. Here, we use calcium imaging and optogenetic approaches to assess the contributions of SOM and PV neurons to stimulus-specific adaptation in the mouse auditory cortex. We find opposing and complementary effects of SOM and PV neurons on the adaptation of principal neurons which manifest as context-dependent SOM neuron-mediated enhancement and PV-neuron mediated suppression of responses that depend on the temporal repetition rate of the sounds. Our results suggest that SOM and PV neurons can engage in multiple operating regimes that exist in a continuum during sensory processing.

Our ability to generalize abstract rules to new situations is a cognitive hallmark, yet its neural basis is unclear. We identified a thalamocortical circuit essential for this process in mice. During a cross-modal rule transfer task, medial prefrontal cortex (mPFC) neurons encoded task rules across sensory modalities to enable generalization. Crucially, mediodorsal thalamus (MD) projections to mPFC were causally required: Inhibiting this pathway destabilized mPFC representations and impaired rule transfer, whereas enhancing it improved performance. Without MD input, mPFC recruited distinct populations for each task, losing cross-context stability. Direct mPFC excitation impaired generalization, underscoring the specificity of thalamic regulation. Thus, the MD stabilizes mPFC activity for flexible rule transfer—a mechanism with implications for cognitive disorders and artificial intelligence.

Memory consolidation enables animals to draw on past experiences to guide future behavior. This process involves system- and synaptic-level changes and predominantly occurs during sleep. While hippocampal-cortical circuits are well studied in this context, the contributions of other systems, including dopaminergic circuits—key players in learning-related processes—remain poorly understood. Ventral tegmental area dopaminergic (VTA DA ) neurons are active during sleep and suggested to participate in memory consolidation processes; however, causal evidence for this is lacking. Using calcium-dependent fiber photometry, electrophysiology, and chemogenetic and optogenetic manipulations across learning paradigms, we explore the functions of VTA DA neuronal activity during sleep. We show that VTA DA activity during nonrapid eye movement sleep is experience dependent, is enhanced by motor skill and associative learning, facilitates motor skill memory consolidation, and exhibits a motor learning–dependent increase in temporal coordination with cortical spindle oscillations. Our findings uncover a previously unidentified function for VTA DA neurons in consolidating memories during sleep, advancing understanding of this central neuromodulator’s functions in regulating fundamental biological processes.

The locus coeruleus–norepinephrine (LC-NE) system regulates arousal and awakening; however, it remains unclear whether the LC does this in a global or circuit-specific manner. We hypothesized that sensory-evoked awakenings are predominantly regulated by specific LC-NE efferent pathways. Anatomical, physiological, and functional modularities of LC-NE pathways involving the mouse basal forebrain (BF) and pontine reticular nucleus (PRN) were tested. We found partial anatomical segregation between the LC → PRN and LC → BF circuits. Extracellular NE dynamics in BF and PRN exhibited distinct sound-evoked activation during sleep, including a fast sound-evoked NE peak specific to PRN. Causal optogenetic interrogation of LC efferent pathways, by retro-channelrhodopsin (ChR2) activation or Platynereis dumerilii ciliary opsin (PdCO) silencing of synapses in target regions, revealed a role for early LC → PRN activity in driving arousal and sound-evoked awakenings. Together, our results uncover a role for early LC-NE PRN activity in connecting sensory and arousal pathways and establish LC heterogeneity in regulating arousal.

Stereocilia are rod-like mechanosensory projections consisting of unidirectionally oriented actin filaments that extend into the inner ear hair cell cytoskeleton, forming dense rootlets. Taperin (TPRN) localizes to the narrowed-down base of stereocilia, where they pivot in response to sound and gravity. We show that TPRN-deficient mice have progressive deafness characterized by gradual asynchronous retraction and fusion of outer and inner hair cell stereocilia, followed by synaptic abnormalities. Stereocilia that lack TPRN develop warped rootlets with gradual loss of TRIOBP-5 and ANKRD24 from mechanosensory rows starting postnatally. In contrast, TPRN overexpression causes excessive F-actin bundling, extra rows, and over-elongation of stereocilia during development. Purified full-length mouse TPRN cross-links F-actin into bendable bundles reflecting in vivo data. This F-actin–bundling ability is attributed to the TPRN N-terminal region. TPRN interacts with the membrane receptor PTPRQ, connecting the F-actin core to the plasma membrane, stabilizing stereocilia. Thus, TPRN is a specialized F-actin bundler strategically located to augment stereocilia rootlet formation and their pivot point flexibility for sustained sound-induced deflections.

The structure of local circuits is highly conserved across the cortex, yet the spatial and temporal properties of population activity differ fundamentally in sensory-level and association-level areas. In the sensory cortex, population activity has a shorter timescale and decays sharply over distance, supporting a population code for the fine-scale features of sensory stimuli. In the association cortex, population activity has a longer timescale and spreads over wider distances, a code that is suited to holding information in memory and driving behavior. We tested whether these differences in activity dynamics could be explained by differences in network structure. We targeted photostimulations to single excitatory neurons of layer 2/3, while monitoring surrounding population activity using two-photon calcium imaging. Experiments were performed in the auditory (AC) and posterior parietal cortex (PPC) within the same mice of both sexes, which also expressed a red fluorophore in somatostatin-expressing interneurons (SOM). In both cortical regions, photostimulations resulted in a spatially restricted zone of positive influence on neurons closely neighboring the targeted neuron and a more spatially diffuse zone of negative influence affecting more distant neurons (akin to a network-level “suppressive surround”). However, the relative spatial extents of positive and negative influence were different in AC and PPC. In PPC, the central zone of positive influence was wider, but the negative suppressive surround was more narrow than in AC, which could account for the larger-scale network dynamics in PPC. The more narrow central positive influence zone and wider suppressive surround in AC could serve to sharpen sensory representations.

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.

The temporal structure of sensory inputs contains essential information for their interpretation. Sensory cortex represents these temporal cues through two codes: the temporal sequences of neuronal activity and the spatial patterns of neuronal firing rate. However, it is unknown which of these coexisting codes causally drives sensory decisions. To separate their contributions, we generated in the mouse auditory cortex optogenetically driven activity patterns differing exclusively along their temporal or spatial dimensions. Mice could rapidly learn to behaviorally discriminate spatial but not temporal patterns. Moreover, large-scale neuronal recordings across the auditory system revealed that the auditory cortex is the first region in which spatial patterns efficiently represent temporal cues on the timescale of several hundred milliseconds. This feature is shared by the deep layers of neural networks categorizing time-varying sounds. Therefore, the emergence of a spatial code for temporal sensory cues is a necessary condition to efficiently associate temporally structured stimuli with decisions.

Introduction Subjective tinnitus, the perception of sound without an external acoustic source, is often subsequent to noise-induced hearing loss or ototoxic medications. The condition is believed to result from neuroplastic alterations in the auditory centers, characterized by heightened spontaneous neural activities and increased synchrony due to an imbalance between excitation and inhibition. However, the role of the thalamic reticular nucleus (TRN), a structure composed exclusively of GABAergic neurons involved in thalamocortical oscillations, in the pathogenesis of tinnitus remains largely unexplored. Methods We induced tinnitus in mice using sodium salicylate and assessed tinnitus-like behaviors using the Gap Pre-Pulse Inhibition of the Acoustic Startle (GPIAS) paradigm. We utilized combined viral tracing techniques to identify the neural circuitry involved and employed immunofluorescence and confocal imaging to determine cell types and activated neurons. Results Salicylate-treated mice exhibited tinnitus-like behaviors. Our tracing clearly delineated the inputs and outputs of the auditory-specific TRN. We discovered that chemogenetic activation of the auditory TRN significantly reduced the salicylate-evoked rise in c-Fos expression in the auditory cortex. Discussion This finding posits the TRN as a potential modulatory target for tinnitus treatment. Furthermore, the mapped sensory inputs to the auditory TRN suggest possibilities for employing optogenetic or sensory stimulations to manipulate thalamocortical activities. The precise mapping of the auditory TRN-mediated neural pathways offers a promising avenue for designing targeted interventions to alleviate tinnitus symptoms.

The entorhinal cortex is involved in establishing enduring visuo-auditory associative memory in the neocortex. Here we explored the mechanisms underlying this synaptic plasticity related to projections from the visual and entorhinal cortices to the auditory cortex in mice using optogenetics of dual pathways. High-frequency laser stimulation (HFS laser) of the visuo-auditory projection did not induce long-term potentiation. However, after pairing with sound stimulus, the visuo-auditory inputs were potentiated following either infusion of cholecystokinin (CCK) or HFS laser of the entorhino-auditory CCK-expressing projection. Combining retrograde tracing and RNAscope in situ hybridization, we show that Cck expression is higher in entorhinal cortex neurons projecting to the auditory cortex than in those originating from the visual cortex. In the presence of CCK, potentiation in the neocortex occurred when the presynaptic input arrived 200 ms before postsynaptic firing, even after just five trials of pairing. Behaviorally, inactivation of the CCK + projection from the entorhinal cortex to the auditory cortex blocked the formation of visuo-auditory associative memory. Our results indicate that neocortical visuo-auditory association is formed through heterosynaptic plasticity, which depends on release of CCK in the neocortex mostly from entorhinal afferents.

The basal ganglia are essential for executing motor actions. How the basal ganglia engage spinal motor networks has remained elusive. Medullary Chx10 gigantocellular (Gi) neurons are required for turning gait programs, suggesting that turning gaits organized by the basal ganglia are executed via this descending pathway. Performing deep brainstem recordings of Chx10 Gi Ca 2+ activity in adult mice, we show that striatal projection neurons initiate turning gaits via a dominant crossed pathway to Chx10 Gi neurons on the contralateral side. Using intersectional viral tracing and cell-type-specific modulation, we uncover the principal basal ganglia–spinal cord pathway for locomotor asymmetries in mice: basal ganglia → pontine reticular nucleus, oral part (PnO) → Chx10 Gi → spinal cord. Modulating the restricted PnO → Chx10 Gi pathway restores turning competence upon striatal damage, suggesting that dysfunction of this pathway may contribute to debilitating turning deficits observed in Parkinson’s disease. Our results reveal the stratified circuit architecture underlying a critical motor program.

Stimulus-specific adaptation (SSA), the reduction of neural activity to a common stimulus that does not generalize to other, rare stimuli, is an essential property of our brain. Although well characterized in adults, it is still unknown how it develops during adolescence and what neuronal circuits are involved. Using in vivo electrophysiology and optogenetics in the lemniscal pathway of the mouse auditory system, we observed SSA to be stable from postnatal day 20 (P20) in the inferior colliculus, to develop until P30 in the auditory thalamus and even later in the primary auditory cortex (A1). We found this maturation process to be experience-dependent in A1 but not in thalamus and to be related to alterations in deep but not input layers of A1. We also identified corticothalamic projections to be implicated in thalamic SSA development. Together, our results reveal different circuits underlying the sequential SSA maturation and provide a unique perspective to understand predictive coding and surprise across sensory systems.

Background: Commonly encountered nontraumatic, moderate noise is increasingly implicated in anxiety; however, the neural substrates underlying this process remain unclear. Objectives: We investigated the neural circuit mechanism through which chronic exposure to moderate-level noise causes anxiety-like behaviors. Methods: Mice were exposed to chronic, moderate white noise [85 decibel (dB) sound pressure level (SPL)], 4 h/d for 4 wk to induce anxiety-like behaviors, which were assessed by open field, elevated plus maze, light-dark box, and social interaction tests. Viral tracing, immunofluorescence confocal imaging, and brain slice patch-clamp recordings were used to characterize projections from auditory brain regions to the lateral amygdala. Neuronal activities were characterized by in vivo multielectrode and fiber photometry recordings in awake mice. Optogenetics and chemogenetics were used to manipulate specific neural circuitry. Results: Mice chronically (4 wk) exposed to moderate noise (85 dB SPL, 4 h/d) demonstrated greater neuronal activity in the lateral amygdala (LA), and the LA played a critical role in noise-induced anxiety-like behavior in these model mice. Viral tracing showed that the LA received monosynaptic projections from the medial geniculate body (MG) and auditory cortex (ACx). Optogenetic excitation of the MG→LA or ACx→LA circuits acutely evoked anxiety-like behaviors, whereas their chemogenetic inactivation abolished noise-induced anxiety-like behavior. Moreover, mice chronically exposed to moderate noise were more susceptible to acute stress, with more neuronal firing in the LA, even after noise withdrawal. Discussion: Mice exposed to 4 wk of moderate noise (85 dB SPL, 4 h/d) demonstrated behavioral and physiological differences compared to controls. The neural circuit mechanisms involved greater excitation from glutamatergic neurons of the MG and ACx to LA neurons under chronic, moderate noise exposure, which ultimately promoted anxiety-like behaviors. Our findings support the hypothesis that nontraumatic noise pollution is a potentially serious but unrecognized public health concern. https://doi.org/10.1289/EHP12532.

Visual stimuli that deviate from the current context elicit augmented responses in the primary visual cortex (V1). These heightened responses, known as "deviance detection," require local inhibition in the V1 and top-down input from the anterior cingulate area (ACa). Here, we investigated the mechanisms by which the ACa and V1 interact to support deviance detection. Local field potential recordings in mice during an oddball paradigm showed that ACa-V1 synchrony peaks in the theta/alpha band (≈10 Hz). Two-photon imaging in the V1 revealed that mainly pyramidal neurons exhibited deviance detection, while contextually redundant stimuli increased vasoactive intestinal peptide (VIP)-positive interneuron (VIP) activity and decreased somatostatin-positive interneuron (SST) activity. Optogenetic drive of ACa-V1 inputs at 10 Hz activated V1-VIPs but inhibited V1-SSTs, mirroring the dynamics present during the oddball paradigm. Chemogenetic inhibition of V1-VIPs disrupted Aca-V1 synchrony and deviance detection in the V1. These results outline temporal and interneuron-specific mechanisms of top-down modulation that support visual context processing.

Sensory cortical areas are robustly modulated by higher-order cortices. Our previous study shows that the anterior cingulate cortex (ACC) can immediately and transiently enhance responses in the mouse auditory cortex (ACx). Here, we further examined whether strong activation of ACC neurons can induce long-term effects in mice of both sexes. To our surprise, only stimulation of cell bodies in the ACC, but not ACC-to-ACx terminal activation, induced long-term enhancement of auditory responses in the ACx. Anatomical examination showed that the ACC indirectly projects to the ACx via the rhinal cortex (RCx). High-frequency stimulation of ACC-projecting terminals to the RCx or RCx-projecting terminals to the ACx induced a similar effect as the cell body activation of ACC neurons, whereas silencing the RCx blocked this long-term enhancement. High-frequency stimulation of ACC projections to the RCx also induced long-term augmentation of sound-evoked flight behavior in male mice. These results show that the ACC promotes the long-term enhancement of auditory responses in the ACx through an indirect pathway via the RCx. SIGNIFICANCE STATEMENT In this study, we demonstrate that the anterior part of the anterior cingulate cortex (ACC) evokes long-term enhancement of auditory responses in the auditory cortex (ACx) when it is strongly activated. Importantly, instead of a direct projection, we show that the ACC implements this effect via an indirect pathway through the lateral rhinal cortex using a series of physiological, optogenetic, anatomic, and behavioral experiments. Along with a short-term effect, this long-term enhancement induced by an indirect ACC-to-ACx projection could increase the odds of survival when animals are faced with threats after a significant event.

Fear and anxiety are brain states that evolved to mediate defensive responses to threats. The defense reaction includes multiple interacting behavioral, autonomic and endocrine adjustments, but their integrative nature is poorly understood. In particular, although threat has been associated with various cardiac changes, there is no clear consensus regarding the relevance of these changes for the integrated defense reaction. Here we identify rapid microstates that are associated with specific behaviors and heart rate dynamics, which are affected by long-lasting macrostates and reflect context-dependent threat levels. In addition, we demonstrate that one of the most commonly used defensive behavioral responses—freezing as measured by immobility—is part of an integrated cardio-behavioral microstate mediated by Chx10 + neurons in the periaqueductal gray. Our framework for systematic integration of cardiac and behavioral readouts presents the basis for a better understanding of complex neural defensive states and their associated systemic functions.

Fear and anxiety are brain states that evolved to mediate defensive responses to threat. While it is clear that the defense reaction includes multiple interacting behavioural, autonomic and endocrine adjustments, their integrative nature is poorly understood. In particular, threat has been associated with various cardiac changes, yet a clear consensus on their relevance for the integrated defense reaction is missing. We here define rapid microstates associated with specific behaviours and heart rate dynamics, both affected by long-lasting macrostates and reflecting context-dependent threat levels. In addition, we demonstrate that one of the most commonly used defensive behavioural responses, freezing measured by immobility, is part of an integrated cardio-behavioural microstate mediated by specific midbrain circuit elements. Our work puts forth a framework for systematic integration of cardiac and behavioural readouts that presents the basis for a better understanding of complex neural defensive states and their associated systemic functions.

Given its inputs from auditory structures and neuromodulatory systems, the posterior tail of the striatum is ideally positioned to influence behavioral responses to acoustic stimuli according to context and previous rewards. Results from previous studies indicate that neurons in this striatal region display selective responses to sounds. However, it is not clear whether different striatal cell classes code for distinct features of sounds or how different striatal output pathways may use acoustic information to guide behavior. Here we compared the sound-evoked responses of posterior striatal neurons that form the striatal direct pathway (and express the dopamine receptor D 1 ) to the responses of neighboring neurons in naive mice. We achieved this via optogenetic photo-identification of D 1 -expressing neurons during extracellular electrophysiological recordings in awake head-fixed mice of both sexes. We found that the frequency tuning of sound-responsive direct-pathway striatal neurons is comparable with that of their sound-responsive neighbors. Moreover, we found that both populations encode amplitude-modulated sounds in a similar fashion. These results suggest that different classes of neurons in the posterior striatum of naive animals have similar access to acoustic features conveyed by the auditory system even outside the context of an auditory task.

Offset responses in auditory processing appear after a sound terminates. They arise in neuronal circuits within the peripheral auditory system, but their role in the central auditory system remains unknown. Here, we ask what the behavioral relevance of cortical offset responses is and what circuit mechanisms drive them. At the perceptual level, our results reveal that experimentally minimizing auditory cortical offset responses decreases the mouse performance to detect sound termination, assigning a behavioral role to offset responses. By combining in vivo electrophysiology in the auditory cortex and thalamus of awake mice, we also demonstrate that cortical offset responses are not only inherited from the periphery but also amplified and generated de novo. Finally, we show that offset responses code more than silence, including relevant changes in sound trajectories. Together, our results reveal the importance of cortical offset responses in encoding sound termination and detecting changes within temporally discontinuous sounds crucial for speech and vocalization.

Although fear memory formation is essential for survival and fear-related mental disorders, the neural circuitry and mechanism are incompletely understood. Here, we utilized trace fear conditioning to study the formation of trace fear memory in mice. We identified the entorhinal cortex (EC) as a critical component of sensory signaling to the amygdala. We adopted both loss-of-function and gain-of-function experiments to demonstrate that release of the cholecystokinin (CCK) from the EC is required for trace fear memory formation. We discovered that CCK-positive neurons project from the EC to the lateral nuclei of the amygdala (LA), and inhibition of CCK-dependent signaling in the EC prevented long-term potentiation of the auditory response in the LA and formation of trace fear memory. In summary, high-frequency activation of EC neurons triggers the release of CCK in their projection terminals in the LA, potentiating auditory response in LA neurons. The neural plasticity in the LA leads to trace fear memory formation.