Clément Léna

SUMMARY: Learning from experience to assess threat is crucial for survival and mental health. This function is known to involve several midbrain areas, notably the ventrolateral periaqueductal grey (vlPAG) and dorsal raphe nuclei (DRN). Recently it has been shown that fear learning involves projections from the cerebellar fastigial nucleus (FN) to the vlPAG. Here, we show using simultaneous single-unit recordings during fear conditioning that a subset of vlPAG/DRN and FN neurons acquire responses to conditioned cues following learning. Strikingly, these populations exhibit firing covariance and directional functional interactions consistent with their collaboration to the response to cues predicting threat. We also demonstrated the reciprocal monosynaptic connectivity between vlPAG/DRN and FN supporting the interactions between these structures. Together, our findings demonstrate shared dynamical activity within a network integrating midbrain and cerebellar computations during fear learning. IN BRIEF: The projections of the cerebellar fastigial nucleus (FN) to the midbrain are involved in associative fear learning. Here, we show that during fear learning FN and periaqueductal grey/dorsal raphe (vlPAG/DRN) neurons acquire simultaneously responses to stimuli predicting aversive stimulus. Moreover, neurons encoding such predictive signals in the FN exhibit coordinated activity with the vlPAG/DRN, with directional functional interactions, suggesting that cerebellar – midbrain interactions contribute to the representation of aversive predictions during fear learning. We further characterize monosynaptic projections from the vlPAG/DRN to the contralateral FN, providing an anatomical substrate for reciprocal communications between the cerebellum and midbrain and extending previous descriptions of this pathway. HIGHLIGHTS: - Cerebellar fastigial (FN) neurons acquire stimulus specific predictive signals during fear learning. - FN neurons encoding predictive signals exhibit coordinated activity and directional functional interactions with vlPAG/DRN neurons. - vlPAG/DRN neurons projecting to the FN elicit short-latency responses in FN neurons. - Reciprocal projections link the FN and vlPAG/DRN providing a potential substrate for cerebellar-midbrain interactions during fear learning.

Motor skill learning is a complex and gradual process that involves the cortex and basal ganglia, both crucial for the acquisition and long-term retention of skills. The cerebellum, which rapidly learns to adjust the movement, connects to the motor cortex and the striatum primarily via the ventral and intralaminar thalamus, respectively. Here, we evaluated the contribution of cerebellar neurons projecting to these thalamic nuclei in a skilled locomotion task in mice. Using a targeted chemogenetic inhibition that preserves the motor abilities, we found that cerebellar nuclei neurons projecting to the intralaminar thalamus contribute to learning and expression, while cerebellar nuclei neurons projecting to the ventral thalamus contribute to offline consolidation. Asymptotic performance, however, required each type of neurons. Thus, our results show that cerebellar neurons belonging to two parallel cerebello-thalamic pathways play distinct, but complementary, roles functioning on different timescales and both necessary for motor skill learning.

Motor skill learning is a complex and gradual process that involves the cortex and basal ganglia, both crucial for the acquisition and long-term retention of skills. The cerebellum, which rapidly learns to adjust the movement, connects to the motor cortex and the striatum primarily via the ventral and intralaminar thalamus respectively. Here, we evaluated the contribution of cerebellar neurons projecting to these thalamic nuclei in a skilled locomotion task in mice. Using a targeted chemogenetic inhibition that preserves the motor abilities, we found that cerebellar nuclei neurons projecting to the intralaminar thalamus contribute to learning and expression, while cerebellar nuclei neurons projecting to the ventral thalamus contribute to offline consolidation. Asymptotic performance, however, required each type of neurons. Thus, our results show that cerebellar neurons belonging to two parallel cerebello-thalamic pathways play distinct, but complementary, roles functioning on different timescales and both necessary for motor skill learning.

Learning a motor skill requires exploring multiple possible solutions to find and retain an optimal strategy. The exploration and consolidation of the motor strategy are usually considered to be segregated respectively between task practice and rest periods. Here we show that two types of offline reactivations of neuronal representations of locomotor strategies in a brain-wide motor circuit are associated with exploration and retention. During short rests between trials, replays of these brainwide representations predict subsequent shifts in strategies indicating that distributed offline processes participate in strategy exploration. Shifts in strategy are consolidated, and their retention follows population reactivation in cerebellar sleep spindles and stabilization of cerebello-cerebral functional connectivity patterns, consistent with the role of spindles in brain plasticity. Overall, motor strategy optimization and consolidation are supported by two intertwined but distinct types of offline distributed reactivation events involving interregional interactions.

The first phase of feeding consists in the procurement of solid foods from the environment by biting, and their preparation for swallowing by chewing. These actions require the precise coordination of tens of orofacial muscles for the jaw and tongue. The seat for this motor patterning is known to reside in the reticular formation, a complex and poorly mapped region of the hindbrain, but the neuron groups involved are still elusive. Here, we characterize a group of excitatory reticular interneurons located in the supratrigeminal area that express the homeodomain transcription factor Phox2b . This nucleus—Sup5 ^Phox2b —is premotor to both jaw-closing and jaw-opening motoneurons and receives direct input from cranial sensory afferents, motor cortex, and satiation related nuclei. Its activity differentially tracks lapping, biting, and chewing movements, suggesting its involvement in the elaboration of distinct orofacial motor patterns in vivo. Acute global activation or inhibition of Sup5 ^Phox2b by optogenetics interrupt volitional feeding sequences. Thus, Sup5 ^Phox2b is an obligatory subcortical node, topologically and genetically defined, in the neural circuits that control the oral phase of feeding in mice.

Decomposing behavior into elementary components remains a central challenge in computational neuroethology. The current standard in laboratory animals involves multi-view video tracking, which, while providing unparalleled access to full-body kinematics, imposes environmental constraints, is data-intensive, and has limited scalability. We present an alternative approach using inertial sensors, which capture high-resolution, environment-independent, and compact three-dimensional kinematic data, and are commonly integrated into rodent neurophysiological devices. Our analysis pipeline leverages unsupervised, computationally efficient change-point detection to break down inertial time series into variable-length, statistically homogeneous segments. These segments are then grouped into candidate behavioral motifs through high-dimensional, model-based probabilistic clustering. We demonstrate that this approach achieves detailed rodent behavioral mapping using head inertial data. Identified motifs, corroborated by video recordings, include orienting movements, grooming components, locomotion, and olfactory exploration. Higher-order behavioral structures can be accessed by applying a categorical hidden Markov model to the motif sequence. Additionally, our pipeline detects both overt and subtle motor changes in a mouse model of Parkinson’s disease and levodopa-induced dyskinesia, highlighting its value for behavioral phenotyping. This methodology offers the possibility of conducting high-resolution, observer-unbiased behavioral analysis at minimal computational cost from easily scalable and environmentally unconstrained recordings.

Motor skill learning is a complex and gradual process that involves the cortex and basal ganglia, both crucial for the acquisition and long-term retention of skills. The cerebellum, which rapidly learns to adjust the movement, connects to the motor cortex and the striatum primarily via the ventral and intralaminar thalamus respectively. Here, we evaluated the contribution of cerebellar neurons projecting to these thalamic nuclei in a skilled locomotion task in mice. Using a targeted chemogenetic inhibition that preserves the motor abilities, we found that cerebellar nuclei neurons projecting to the intralaminar thalamus contribute to learning and expression, while cerebellar nuclei neurons projecting to the ventral thalamus contribute to offline consolidation. Asymptotic performance, however, required each type of neurons. Thus, our results show that cerebellar neurons belonging to two parallel cerebello-thalamic pathways play distinct, but complementary, roles functioning on different timescales and both necessary for motor skill learning.

Microglia sense the changes in their environment. How microglia actively translate these changes into suitable cues to adapt brain physiology is unknown. We reveal an activity-dependent regulation of cortical inhibitory synapses by microglia, driven by purinergic signaling acting on P2RX7 and mediated by microglia-derived TNFα. We demonstrate that sleep induces microglia-dependent synaptic enrichment of GABAARs in a manner dependent on microglial TNFα and P2RX7. We further show that microglia-specific depletion of TNFα alters slow waves during NREM sleep and blunt memory consolidation in sleep-dependent learning tasks. Together, our results reveal that microglia orchestrate sleep-intrinsic plasticity of synaptic GABAARs, sculpt sleep slow waves, and support memory consolidation.

Fear learning is mediated by a large network of brain structures and the understanding of their roles and interactions is constantly progressing. There is a multitude of anatomical and behavioral evidence on the interconnection of the cerebellar nuclei to other structures in the fear network. Regarding the cerebellar nuclei, we focus on the coupling of the cerebellar fastigial nucleus to the fear network and the relation of the cerebellar dentate nucleus to the ventral tegmental area. Many of the fear network structures that receive direct projections from the cerebellar nuclei are playing a role in fear expression or in fear learning and fear extinction learning. We propose that the cerebellum, via its projections to the limbic system, acts as a modulator of fear learning and extinction learning, using prediction-error signaling and regulation of fear related thalamo-cortical oscillations.

Fear extinction is a form of inhibitory learning that suppresses the expression of aversive memories and plays a key role in the recovery of anxiety and trauma-related disorders. Here, using male mice, we identify a cerebello-thalamo-cortical pathway regulating fear extinction. The cerebellar fastigial nucleus (FN) projects to the lateral subregion of the mediodorsal thalamic nucleus (MD), which is reciprocally connected with the dorsomedial prefrontal cortex (dmPFC). The inhibition of FN inputs to MD in male mice impairs fear extinction in animals with high fear responses and increases the bursting of MD neurons, a firing pattern known to prevent extinction learning. Indeed, this MD bursting is followed by high levels of the dmPFC 4 Hz oscillations causally associated with fear responses during fear extinction, and the inhibition of FN-MD neurons increases the coherence of MD bursts and oscillations with dmPFC 4 Hz oscillations. Overall, these findings reveal a regulation of fear-related thalamo-cortical dynamics by the cerebellum and its contribution to fear extinction.