Combinatorial Targeting of Distributed Forebrain Networks Reverses Noise Hypersensitivity in a Model of Autism Spectrum Disorder

Developing algorithmic psychiatry via multi-level spanning computational models

Modern psychiatry faces challenges in translating neurobiological insights into treatments for severe illnesses. The mid-20th century witnessed the rise of molecular mechanisms as pathophysiological and treatment models, with recent holistic proposals keeping this focus unaltered. In this perspective, we explore how psychiatry can utilize systems neuroscience to develop a vertically integrated understanding of brain function to inform treatment. Using schizophrenia as a case study, we discuss scale-related challenges faced by researchers studying molecules, circuits, networks, and cognition and clinicians operating within existing frameworks. We emphasize computation as a bridging language, with algorithmic models like hierarchical predictive processing offering explanatory potential for targeted interventions. Developing such models will not only facilitate new interventions but also optimize combining existing treatments by predicting their multi-level effects. We conclude with the prognosis that the future is bright, but that continued investment in research closely driven by clinical realities will be critical.

A prefrontal thalamocortical readout for conflict-related executive dysfunction in schizophrenia

Executive dysfunction is a prominent feature of schizophrenia and may drive core symptoms. Dorsolateral prefrontal cortex (dlPFC) deficits have been linked to schizophrenia executive dysfunction, but mechanistic details critical for treatment development remain unclear. Here, capitalizing on recent animal circuit studies, we develop a task predicted to engage human dlPFC and its interactions with the mediodorsal thalamus (MD). We find that individuals with schizophrenia exhibit selective performance deficits when attention is guided by conflicting cues. Task performance correlates with lateralized MD-dlPFC functional connectivity, identifying a neural readout that predicts susceptibility to conflict during working memory in a larger independent schizophrenia cohort. In healthy subjects performing a probabilistic reversal task, this MD-dlPFC network predicts switching behavior. Overall, our three independent experiments introduce putative biomarkers for executive function in schizophrenia and highlight animal circuit studies as inspiration for the development of clinically relevant readouts.

Rapid context inference in a thalamocortical model using recurrent neural networks

Cognitive flexibility is a fundamental ability that enables humans and animals to exhibit appropriate behaviors in various contexts. The thalamocortical interactions between the prefrontal cortex (PFC) and the mediodorsal thalamus (MD) have been identified as crucial for inferring temporal context, a critical component of cognitive flexibility. However, the neural mechanism responsible for context inference remains unknown. To address this issue, we propose a PFC-MD neural circuit model that utilizes a Hebbian plasticity rule to support rapid, online context inference. Specifically, the model MD thalamus can infer temporal contexts from prefrontal inputs within a few trials. This is achieved through the use of PFC-to-MD synaptic plasticity with pre-synaptic traces and adaptive thresholding, along with winner-take-all normalization in the MD. Furthermore, our model thalamus gates context-irrelevant neurons in the PFC, thus facilitating continual learning. We evaluate our model performance by having it sequentially learn various cognitive tasks. Incorporating an MD-like component alleviates catastrophic forgetting of previously learned contexts and demonstrates the transfer of knowledge to future contexts. Our work provides insight into how biological properties of thalamocortical circuits can be leveraged to achieve rapid context inference and continual learning.

Thalamocortical architectures for flexible cognition and efficient learning

The brain exhibits a remarkable ability to learn and execute context-appropriate behaviors. How it achieves such flexibility, without sacrificing learning efficiency, is an important open question. Neuroscience, psychology, and engineering suggest that reusing and repurposing computations are part of the answer. Here, we review evidence that thalamocortical architectures may have evolved to facilitate these objectives of flexibility and efficiency by coordinating distributed computations. Recent work suggests that distributed prefrontal cortical networks compute with flexible codes, and that the mediodorsal thalamus provides regularization to promote efficient reuse. Thalamocortical interactions resemble hierarchical Bayesian computations, and their network implementation can be related to existing gating, synchronization, and hub theories of thalamic function. By reviewing recent findings and providing a novel synthesis, we highlight key research horizons integrating computation, cognition, and systems neuroscience.

Impaired cerebellar plasticity hypersensitizes sensory reflexes in SCN2A-associated ASD

Children diagnosed with autism spectrum disorder (ASD) commonly present with sensory hypersensitivity or abnormally strong reactions to sensory stimuli. Such hypersensitivity can be overwhelming, causing high levels of distress that contribute markedly to the negative aspects of the disorder. Here, we identify a mechanism that underlies hypersensitivity in a sensorimotor reflex found to be altered in humans and in mice with loss of function in the ASD risk-factor gene SCN2A. The cerebellum-dependent vestibulo-ocular reflex (VOR), which helps maintain one's gaze during movement, was hypersensitized due to deficits in cerebellar synaptic plasticity. Heterozygous loss of SCN2A-encoded NaV1.2 sodium channels in granule cells impaired high-frequency transmission to Purkinje cells and long-term potentiation, a form of synaptic plasticity important for modulating VOR gain. VOR plasticity could be rescued in mice via a CRISPR-activator approach that increases Scn2a expression, demonstrating that evaluation of a simple reflex can be used to assess and quantify successful therapeutic intervention.

Sound elicits stereotyped facial movements that provide a sensitive index of hearing abilities in mice

Sound elicits rapid movements of muscles in the face, ears, and eyes that protect the body from injury and trigger brain-wide internal state changes. Here, we performed quantitative facial videography from mice resting atop a piezoelectric force plate and observed that broadband sounds elicited rapid and stereotyped facial twitches. Facial motion energy (FME) adjacent to the whisker array was 30 dB more sensitive than the acoustic startle reflex and offered greater inter-trial and inter-animal reliability than sound-evoked pupil dilations or movement of other facial and body regions. FME tracked the low-frequency envelope of broadband sounds, providing a means to study behavioral discrimination of complex auditory stimuli, such as speech phonemes in noise. Approximately 25% of layer 5-6 units in the auditory cortex (ACtx) exhibited firing rate changes during facial movements. However, FME facilitation during ACtx photoinhibition indicated that sound-evoked facial movements were mediated by a midbrain pathway and modulated by descending corticofugal input. FME and auditory brainstem response (ABR) thresholds were closely aligned after noise-induced sensorineural hearing loss, yet FME growth slopes were disproportionately steep at spared frequencies, reflecting a central plasticity that matched commensurate changes in ABR wave 4. Sound-evoked facial movements were also hypersensitive in Ptchd1 knockout mice, highlighting the use of FME for identifying sensory hyper-reactivity phenotypes after adult-onset hyperacusis and inherited deficiencies in autism risk genes. These findings present a sensitive and integrative measure of hearing while also highlighting that even low-intensity broadband sounds can elicit a complex mixture of auditory, motor, and reafferent somatosensory neural activity.

The mediodorsal thalamus in executive control

Executive control, the ability to organize thoughts and action plans in real time, is a defining feature of higher cognition. Classical theories have emphasized cortical contributions to this process, but recent studies have reinvigorated interest in the role of the thalamus. Although it is well established that local thalamic damage diminishes cognitive capacity, such observations have been difficult to inform functional models. Recent progress in experimental techniques is beginning to enrich our understanding of the anatomical, physiological, and computational substrates underlying thalamic engagement in executive control. In this review, we discuss this progress and particularly focus on the mediodorsal thalamus, which regulates the activity within and across frontal cortical areas. We end with a synthesis that highlights frontal thalamocortical interactions in cognitive computations and discusses its functional implications in normal and pathological conditions.

Restoring the Function of Thalamocortical Circuit Through Correcting Thalamic Kv3.2 Channelopathy Normalizes Fear Extinction Impairments in a PTSD Mouse Model

Impaired extinction of fear memory is one of the most common symptoms in post-traumatic stress disorder (PTSD), with limited therapeutic strategies due to the poor understanding of its underlying neural substrates. In this study, functional screening is performed and identified hyperactivity in the mediodorsal thalamic nucleus (MD) during fear extinction. Furthermore, the encoding patterns of the hyperactivated MD is investigated during persistent fear responses using multiple machine learning algorithms. The anterior cingulate cortex (ACC) is also identified as a functional downstream region of the MD that mediates the extinction of fear memory. The thalamocortical circuit is comprehensively analyzed and found that the MD-ACC parvalbumin interneurons circuit is preferentially enhanced in PTSD mice, disrupting the local excitatory and inhibitory balance. It is found that decreased phosphorylation of the Kv3.2 channel contributed to the hyperactivated MD, primarily to the malfunctioning thalamocortical circuit. Using a lipid nanoparticle-based RNA therapy strategy, channelopathy is corrected via a methoxylated siRNA targeting the protein phosphatase 6 catalytic subunit and restored fear memory extinction in PTSD mice. These findings highlight the function of the thalamocortical circuit in PTSD-related impaired extinction of fear memory and provide therapeutic insights into Kv3.2-targeted RNA therapy for PTSD.

Modulation of prefrontal couplings by prior belief-related responses in ventromedial prefrontal cortex

Humans and other animals can maintain constant payoffs in an uncertain environment by steadily re-evaluating and flexibly adjusting current strategy, which largely depends on the interactions between the prefrontal cortex (PFC) and mediodorsal thalamus (MD). While the ventromedial PFC (vmPFC) represents the level of uncertainty (i.e., prior belief about external states), it remains unclear how the brain recruits the PFC-MD network to re-evaluate decision strategy based on the uncertainty. Here, we leverage non-linear dynamic causal modeling on fMRI data to test how prior belief-dependent activity in vmPFC gates the information flow in the PFC-MD network when individuals switch their decision strategy. We show that the prior belief-related responses in vmPFC had a modulatory influence on the connections from dorsolateral PFC (dlPFC) to both, lateral orbitofrontal (lOFC) and MD. Bayesian parameter averaging revealed that only the connection from the dlPFC to lOFC surpassed the significant threshold, which indicates that the weaker the prior belief, the less was the inhibitory influence of the vmPFC on the strength of effective connections from dlPFC to lOFC. These findings suggest that the vmPFC acts as a gatekeeper for the recruitment of processing resources to re-evaluate the decision strategy in situations of high uncertainty.

Degraded tactile coding in the Cntnap2 mouse model of autism

Atypical sensory processing in autism involves altered neural circuit function and neural coding in sensory cortex, but the nature of coding disruption is poorly understood. We characterized neural coding in L2/3 of whisker somatosensory cortex (S1) of Cntnap2-/- mice, an autism model with pronounced hypofunction of parvalbumin (PV) inhibitory circuits. We tested for both excess spiking, which is often hypothesized in autism models with reduced inhibition, and alterations in somatotopic coding, using c-fos immunostaining and 2-photon calcium imaging in awake mice. In Cntnap2-/- mice, c-fos-(+) neuron density was elevated in L2/3 of S1 under spontaneous activity conditions, but comparable to control mice after whisker stimulation, suggesting that sensory-evoked spiking was relatively normal. 2-photon GCaMP8m imaging in L2/3 pyramidal cells revealed no increase in whisker-evoked response magnitude, but instead showed multiple signs of degraded somatotopic coding. These included broadening of whisker tuning curves, blurring of the whisker map, and blunting of the point representation of each whisker. These altered properties were more pronounced in noisy than sparse sensory conditions. Tuning instability, assessed over 2-3 weeks of longitudinal imaging, was also significantly increased in Cntnap2-/- mice. Thus, Cntnap2-/- mice show no excess spiking, but a degraded and unstable tactile code in S1.

Impaired cerebellar plasticity hypersensitizes sensory reflexes in SCN2A-associated ASD

Children diagnosed with autism spectrum disorder (ASD) commonly present with sensory hypersensitivity, or abnormally strong reactions to sensory stimuli. Such hypersensitivity can be overwhelming, causing high levels of distress that contribute markedly to the negative aspects of the disorder. Here, we identify the mechanisms that underlie hypersensitivity in a sensorimotor reflex found to be altered in humans and in mice with loss-of-function in the ASD risk-factor gene SCN2A. The cerebellum-dependent vestibulo-ocular reflex (VOR), which helps maintain one's gaze during movement, was hypersensitized due to deficits in cerebellar synaptic plasticity. Heterozygous loss of SCN2A-encoded NaV1.2 sodium channels in granule cells impaired high-frequency transmission to Purkinje cells and long-term potentiation, a form of synaptic plasticity important for modulating VOR gain. VOR plasticity could be rescued in adolescent mice via a CRISPR-activator approach that increases Scn2a expression, highlighting how evaluation of simple reflexes can be used as quantitative readout of therapeutic interventions.

Reversal of hyperactive higher-order thalamus attenuates defensiveness in a mouse model of PTSD

Posttraumatic stress disorder (PTSD) is a highly prevalent and debilitating psychiatric disease often accompanied by severe defensive behaviors, preventing individuals from integrating into society. However, the neural mechanisms of defensiveness in PTSD remain largely unknown. Here, we identified that the higher-order thalamus, the posteromedial complex of the thalamus (PoM), was overactivated in a mouse model of PTSD, and suppressing PoM activity alleviated excessive defensive behaviors. Moreover, we found that diminished thalamic inhibition derived from the thalamic reticular nucleus was the major cause of thalamic hyperactivity in PTSD mice. Overloaded thalamic innervation to the downstream cortical area, frontal association cortex, drove abnormal defensiveness. Overall, our study revealed that the malfunction of the higher-order thalamus mediates defensive behaviors and highlighted the thalamocortical circuit as a potential target for treating PTSD-related overreactivity symptoms.

Mechanisms Underlying Circuit Dysfunction in Neurodevelopmental Disorders

Recent advances in genomics have revealed a wide spectrum of genetic variants associated with neurodevelopmental disorders at an unprecedented scale. An increasing number of studies have consistently identified mutations-both inherited and de novo-impacting the function of specific brain circuits. This suggests that, during brain development, alterations in distinct neural circuits, cell types, or broad regulatory pathways ultimately shaping synapses might be a dysfunctional process underlying these disorders. Here, we review findings from human studies and animal model research to provide a comprehensive description of synaptic and circuit mechanisms implicated in neurodevelopmental disorders. We discuss how specific synaptic connections might be commonly disrupted in different disorders and the alterations in cognition and behaviors emerging from imbalances in neuronal circuits. Moreover, we review new approaches that have been shown to restore or mitigate dysfunctional processes during specific critical windows of brain development. Considering the heterogeneity of neurodevelopmental disorders, we also highlight the recent progress in developing improved clinical biomarkers and strategies that will help to identify novel therapeutic compounds and opportunities for early intervention.

Auditory processing in rodent models of autism: a systematic review

Autism is a complex condition with many traits, including differences in auditory sensitivity. Studies in human autism are plagued by the difficulty of controlling for aetiology, whereas studies in individual rodent models cannot represent the full spectrum of human autism. This systematic review compares results in auditory studies across a wide range of established rodent models of autism to mimic the wide range of aetiologies in the human population. A search was conducted in the PubMed and Web of Science databases to find primary research articles in mouse or rat models of autism which investigate central auditory processing. A total of 88 studies were included. These used non-invasive measures of auditory function, such as auditory brainstem response recordings, cortical event-related potentials, electroencephalography, and behavioural tests, which are translatable to human studies. They also included invasive measures, such as electrophysiology and histology, which shed insight on the origins of the phenotypes found in the non-invasive studies. The most consistent results across these studies were increased latency of the N1 peak of event-related potentials, decreased power and coherence of gamma activity in the auditory cortex, and increased auditory startle responses to high sound levels. Invasive studies indicated loss of subcortical inhibitory neurons, hyperactivity in the lateral superior olive and auditory thalamus, and reduced specificity of responses in the auditory cortex. This review compares the auditory phenotypes across rodent models and highlights those that mimic findings in human studies, providing a framework and avenues for future studies to inform understanding of the auditory system in autism.

PTCHD1: Identification and Neurodevelopmental Contributions of an Autism Spectrum Disorder and Intellectual Disability Susceptibility Gene

Over the last one and a half decades, copy number variation and whole-genome sequencing studies have illuminated the considerable genetic heterogeneity that underlies the etiologies of autism spectrum disorder (ASD) and intellectual disability (ID). These investigations support the idea that ASD may result from complex interactions between susceptibility-related genetic variants (single nucleotide variants or copy number variants) and the environment. This review outlines the identification and neurobiological characterization of two such genes located in Xp22.11, Patched domain-containing 1 (PTCHD1), and its antisense lncRNA PTCHD1-AS. Animal models of Ptchd1 disruption have recapitulated a subset of clinical symptoms related to ASD as well as to ID. Furthermore, these Ptchd1 mouse knockout studies implicate the expression of Ptchd1 in both the thalamic and the hippocampal brain regions as being crucial for proper neurodevelopment and cognitive function. Altered kynurenine metabolic signalling has been postulated as a disease mechanism in one of these animal studies. Additionally, ASD patient-derived induced pluripotent stem cells (iPSCs) carrying a copy number loss impacting the antisense non-coding RNA PTCHD1-AS have been used to generate 2D neuronal cultures. While copy number loss of PTCHD1-AS does not affect the transcription of PTCHD1, the neurons exhibit diminished miniature excitatory postsynaptic current frequency, supporting its role in ASD etiology. A more thorough understanding of risk factor genes, such as PTCHD1 and PTCHD1-AS, will help to clarify the intricate genetic and biological mechanisms that underlie ASD and ID, providing a foundation for meaningful therapeutic interventions to enhance the quality of life of individuals who experience these conditions.

Anterior thalamic dysfunction underlies cognitive deficits in a subset of neuropsychiatric disease models

Neuropsychiatric disorders are often accompanied by cognitive impairments/intellectual disability (ID). It is not clear whether there are converging mechanisms underlying these debilitating impairments. We found that many autism and schizophrenia risk genes are expressed in the anterodorsal subdivision (AD) of anterior thalamic nuclei, which has reciprocal connectivity with learning and memory structures. CRISPR-Cas9 knockdown of multiple risk genes selectively in AD thalamus led to memory deficits. While the AD is necessary for contextual memory encoding, the neighboring anteroventral subdivision (AV) regulates memory specificity. These distinct functions of AD and AV are mediated through their projections to retrosplenial cortex, using differential mechanisms. Furthermore, knockdown of autism and schizophrenia risk genes PTCHD1, YWHAG, or HERC1 from AD led to neuronal hyperexcitability, and normalization of hyperexcitability rescued memory deficits in these models. This study identifies converging cellular to circuit mechanisms underlying cognitive deficits in a subset of neuropsychiatric disease models.

Involvement of the thalamic reticular nucleus in prepulse inhibition of acoustic startle

Thalamic reticular nucleus (TRN) is a group of inhibitory neurons surrounding the thalamus. Due to its important role in sensory information processing, TRN is considered as the target nucleus for the pathophysiological investigation of schizophrenia and autism spectrum disorder (ASD). Prepulse inhibition (PPI) of acoustic startle response, a phenomenon that strong stimulus-induced startle reflex is reduced by a weaker prestimulus, is always found impaired in schizophrenia and ASD. But the role of TRN in PPI modulation remains unknown. Here, we report that parvalbumin-expressing (PV+) neurons in TRN are activated by sound stimulation of PPI paradigm. Chemogenetic inhibition of PV+ neurons in TRN impairs PPI performance. Further investigations on the mechanism suggest a model of burst-rebound burst firing in TRN-auditory thalamus (medial geniculate nucleus, MG) circuitry. The burst firing is mediated by T-type calcium channel in TRN, and rebound burst firing needs the participation of GABAB receptor in MG. Overall, these findings support the involvement of TRN in PPI modulation.

Variation of connectivity across exemplar sensory and associative thalamocortical loops in the mouse

The thalamus engages in sensation, action, and cognition, but the structure underlying these functions is poorly understood. Thalamic innervation of associative cortex targets several interneuron types, modulating dynamics and influencing plasticity. Is this structure-function relationship distinct from that of sensory thalamocortical systems? Here, we systematically compared function and structure across a sensory and an associative thalamocortical loop in the mouse. Enhancing excitability of mediodorsal thalamus, an associative structure, resulted in prefrontal activity dominated by inhibition. Equivalent enhancement of medial geniculate excitability robustly drove auditory cortical excitation. Structurally, geniculate axons innervated excitatory cortical targets in a preferential manner and with larger synaptic terminals, providing a putative explanation for functional divergence. The two thalamic circuits also had distinct input patterns, with mediodorsal thalamus receiving innervation from a diverse set of cortical areas. Altogether, our findings contribute to the emerging view of functional diversity across thalamic microcircuits and its structural basis.

Synaptic properties of the feedback connections from the thalamic reticular nucleus to the dorsal lateral geniculate nucleus

The thalamic reticular nucleus (TRN) is a shell-like structure comprised of GABAergic neurons that surrounds the dorsal thalamus. While playing a key role in modulating thalamocortical interactions, TRN inhibition of thalamic activity is often thought of as having an all-or-none impact. Although TRN neurons have a dynamic firing range, it remains unclear how variable rates of TRN activity gate thalamocortical transmission. To address this, we examined the ultrastructural features and functional synaptic properties of the feedback connections in the mouse thalamus between TRN and the dorsal lateral geniculate nucleus (dLGN), the principal relay of retinal signals to visual cortex. Using electron microscopy to identify TRN input to dLGN, we found that TRN terminals formed synapses with non-GABAergic postsynaptic profiles. Compared with other nonretinal terminals in dLGN, those from TRN were relatively large and tended to contact proximal regions of relay cell dendrites. To evoke TRN activity in dLGN, we adopted an optogenetic approach by expressing ChR2, or a variant (ChIEF) in TRN terminals. Both in vitro and in vivo recordings revealed that repetitive stimulation of TRN terminals led to a frequency-dependent inhibition of dLGN activity, with higher rates of stimulation resulting in increasing levels of membrane hyperpolarization and corresponding decreases in spike firing. This relationship suggests that alterations in TRN activity lead to graded changes in relay cell spike firing.NEW & NOTEWORTHY The thalamic reticular nucleus (TRN) modulates thalamocortical transmission through inhibition. In mouse, TRN terminals in the dorsal lateral geniculate nucleus (dLGN) form synapses with relay neurons but not interneurons. Stimulation of TRN terminals in dLGN leads to a frequency-dependent form of inhibition, with higher rates of stimulation leading to a greater suppression of spike firing. Thus, TRN inhibition appears more dynamic than previously recognized, having a graded rather than an all-or-none impact on thalamocortical transmission.