Frontiers in Neural Circuits

Ascending propriospinal modulation of thoracic sympathetic preganglionic neurons during lumbar locomotor activity

2026-03-20

Lucia E. Dominguez-Rodriguez, Chioma V. Nwachukwu, Narjes Shahsavani, Juanita Garcia, Jeremy W. Chopek, Kristine C. Cowley

Although the autonomic sympathetic system is activated in parallel with locomotion, the underlying neural mechanisms mediating this coordination are not completely understood. Descending exercise or “central command” signals from hypothalamic and brainstem regions are thought to activate thoracic spinal sympathetic neurons in parallel with descending locomotor commands. In turn, subsets of thoracic sympathetic preganglionic neurons (SPNs) increase activity in a constellation of tissues and organs that provide homeostatic and metabolic support during movement and exercise. It is known that ascending drive from lumbar locomotor networks is mediated in part via propriospinal neurons that can also activate and coordinate autonomic systems. However, the extent to which this ascending drive is distributed to SPNs within thoracic regions is unknown. To investigate this, we applied neurochemicals to elicit whole-cord or lumbar-evoked locomotor activity in an in vitro spinal cord preparation, simultaneously recording lumbar ventral root (VR) activity and changes in normalized calcium fluorescence (Ca-RI) of pre-labelled SPNs in thoracic segments. Using whole-bath drug application SPN responses appeared unimodal, such that SPN Ca-RI was increased in rostral (T4-FT7) compared to caudal (T8-T11) segments during tonic activity. During rhythmic activity in either whole or split-bath configuration, and during tonic activity in split-bath configuration, SPN responses appeared trimodal, such that SPN Ca-RI was increased in mid-thoracic segments (T6-7) and reduced at more rostral (T4-5) and caudal (T8-9) levels. In both approaches, the greatest increases in SPNs Ca-RI during rhythmic activity were at T6-7, and most decreased at caudal segments (T8-T11). Together, these findings reveal a strong ascending lumbar to thoracic integrating communication pathway, which may represent a key feature of spinal neural network function normally. Such communication pathways should be further investigated for targeted autonomic function(s) activation and therapeutic benefit after spinal cord injury.

Editorial: Chemical senses in health and disease

2026-03-17

Carla Mucignat-Caretta, Sachiko Koyama, Vera V. Voznessenskaya

Absence of local retinotopy in the mouse optic tract

2026-03-03

Matteo Tripodi, Hiroki Asari

Retinotopy is a fundamental organizational principle of the visual system, where neighboring neurons represent adjacent points in visual space. This spatial relationship is established by precise anatomical wiring across successive areas, e.g., from the retina to the lateral geniculate nucleus (LGN) to the visual cortex. To examine the precision of this topographic arrangement within the long-range projection axons themselves, we recorded retinal ganglion cell (RGC) axons in the mouse optic tract (OT) and mapped their receptive fields (RFs). As expected for a retinotopically organized area, we found that nearby LGN cell pairs had significantly smaller RF distances than distant pairs. In contrast, no such relationship was observed among RGC axons in the OT. Modelling analyses further confirmed that the observed RF distances in the OT were incompatible with any locally retinotopic arrangement. Instead, the OT retained only coarse topography, with ~18° RF deviations or ~40 μm axonal displacements from an ideal retinotopic organization. These results demonstrate that the mouse OT lacks fine-scale retinotopy and maintains only broad topographic structure.

Social learning and exploration–exploitation dilemma in decision-making

2026-03-02

Gota Morishita, Shinsuke Suzuki

This mini review examines the neurocomputational principles of social learning through the lens of the exploration–exploitation dilemma. While the neural mechanisms of learning from others—mediated by distinct signals in the ventromedial and lateral prefrontal cortices—are well established, less is known about how these mechanisms interact with the fundamental trade-off between gathering information (“exploration”) and maximizing rewards (“exploitation”). We discuss how social environments shape this trade-off, leading to strategic behaviors such as informational free-riding or conformity. A central focus of this review is the issue of source selection: how agents decide whom to observe. We present recent evidence suggesting that, contrary to the predictions of optimal information-seeking theories, humans often exhibit a “reliability-seeking” bias, preferring to learn from consistent, exploitation-oriented partners rather than highly exploratory ones. We conclude by discussing the limitations of current paradigms, specifically the inherent confounding of social cues such as competence and predictability, and outline a computational framework for isolating the specific drivers of adaptive social decision-making.

The cerebellum engages multiple pre-motor pathways through a divergent-convergent architecture to shape whisker dynamics

2026-01-22

Staf Bauer, Peipei Zhai, Nathalie van Wingerden, Hehe Zhao, Vincenzo Romano

The cerebellar output can trigger whisker movement through indirect projections that pass via several brainstem pre-motor nuclei before reaching the facial nucleus, which directly controls whisker movements in rodents. Although the central pattern generator function of the intermediate reticular formation has been recently clarified, the roles of the other whisker pre-motor nuclei remain unclear. Here, we set out to compare the whisker movement kinematics of the main pre-motor whisker nuclei connecting the cerebellum and the facial nucleus. We optogenetically stimulated neurons located in the cerebellar cortex: Purkinje cells (PCs), the cerebellar nuclei (CN), the red nucleus (RN), the superior colliculus (SC), the spinal trigeminal nucleus (SV), and the reticular formation (RF); in head-fixed awake mice while monitoring the bilateral whisker movement. We show that optogenetic stimulation of the RN, SC, and SV resulted in a predominant midpoint change, whereas optogenetic stimulation of the PCs, CN, and RF resulted in faster whisker movements. In addition, the excitation of PCs, the RN, and SC resulted in symmetric bilateral whisking. In contrast, the excitation of the RF, and SV resulted in initial asymmetric movement, followed by a more dominantly symmetrical bilateral whisking. Importantly, PC excitation generated a robust rhythmic whisking pattern that could not be reproduced by direct CN stimulation, indicating that the cerebellar cortex sculpts CN population output rather than simply gating it. Our results suggest that cerebellar output engages multiple, specialized pre-motor pathways through a divergent-convergent architecture. This system allows different pre-motor nuclei to modulate distinct aspects of whisking kinematics, ultimately shaping whisker motor dynamics.

Editorial: Bridging computation, biophysics, medicine, and engineering in neural circuits

2026-01-21

Haruyuki Kamiya, Hideaki Yamamoto, Jordi Soriano, Shigeo Sato, Toshiaki Omori

Morphological and transcriptomic change of brain pericytes by lipopolysaccharide treatment

2026-01-20

Taiki Asai, Yoshino Yonezu, Akiko Uyeda, Haruki Watanabe, Tatsunori Suzuki, Hidemi Misawa, Rieko Muramatsu

Brain pericytes play essential roles in vascular homeostasis, including capillary stabilization and maintenance of the blood–brain barrier. Lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, is known to trigger inflammatory responses not only systemically but also within the central nervous system. In this study, we investigated the effects of LPS on the phenotype and transcriptome of brain vascular pericytes. LPS promoted bromodeoxyuridine incorporation in the primary culture of human brain pericytes as well as increased the number of Ki67-positive cells, indicating enhanced pericyte proliferation. Morphological analysis revealed that LPS decreased the cellular aspect ratio, suggesting altered cellular elongation. Transcriptomic profiling showed that LPS-induced differentially expressed genes were enriched for terms related to cell proliferation, angiogenesis, and blood–brain barrier function. Because pericytes critically regulate neurovascular coupling and metabolic support for active neurons, these LPS-induced alterations may ultimately perturb the microvascular control of neural circuits. These results suggest that LPS has the potential to regulate brain vascular function by inducing morphological and functional changes in pericytes.

Frequency-specific intermuscular coherence of synergistic muscles during an isometric force generation task

2025-11-07

Daniele Borzelli, Alberto Cacciola, Carlo Vittorio Cannistraci, Angelo Alito, Demetrio Milardi, Andrea d’Avella

IntroductionMotor tasks require the flexible selection and coordination of multiple muscles, which may be achieved through the organization and combination of muscle synergies. Although multiple muscles may receive a shared neural drive, and each muscle may also receive distinct neural inputs, there is ongoing debate about whether synergies accurately reflect shared neural drives. This study aimed to compare the spectral characteristics of the common drive shared among muscles within the same synergy to those shared among muscles belonging to different synergies.MethodsElectromyographic signals were recorded from upper limb muscles during an isometric multi-directional force generation task. Synergies were identified using non-negative matrix factorization (NMF), and coherence analysis was conducted to evaluate common drives among muscles within and across synergies. A methodological limitation of previous studies was to segment muscle activity into standard frequency bands. Here, we overcome it by proposing to automatically detect subject-specific and physiologically relevant frequency layers. The application of NMF on the coherence spectra of muscle pairs as a method for automatically detecting physiologically relevant frequency bands sheds light into the neural basis of muscle coordination.ResultsSix frequency layers were identified, and muscle recruited within the same synergy showed a higher coherence within layers in the delta, alpha, and low-beta bands.DiscussionOur findings enhance the understanding of physiological mechanisms of motor coordination by elucidating the relationship between muscle synergies and the spectral characteristics of intermuscular coherence.

Emergent functions of noise-driven spontaneous activity: homeostatic maintenance of criticality and memory consolidation

2025-10-23

Narumitsu Ikeda, Dai Akita, Hirokazu Takahashi

Unlike digital computers, the brain exhibits spontaneous activity even during complete rest, despite the evolutionary pressure for energy efficiency. Inspired by the critical brain hypothesis, which proposes that the brain operates optimally near a critical point of phase transition in the dynamics of neural networks to improve computational efficiency, we postulate that spontaneous activity plays a homeostatic role in the development and maintenance of criticality. Criticality in the brain is associated with the balance between excitatory and inhibitory synaptic inputs (EI balance), which is essential for maintaining neural computation performance. Here, we hypothesize that both criticality and EI balance are stabilized by appropriate noise levels and spike-timing-dependent plasticity (STDP) windows. Using spiking neural network (SNN) simulations and in vitro experiments with dissociated neuronal cultures, we demonstrated that while repetitive stimuli transiently disrupt both criticality and EI balance, spontaneous activity can develop and maintain these properties and prolong the fading memory of past stimuli. Our findings suggest that the brain may achieve self-optimization and memory consolidation as emergent functions of noise-driven spontaneous activity. This noise-harnessing mechanism provides insights for designing energy-efficient neural networks, and suggest a potential link between the emergent function of spontaneous activity and sleep function in maintaining homeostasis and consolidating memory.

Feedforward extraction of behaviorally significant information by neocortical columns

2025-10-07

Oleg V. Favorov, Olcay Kursun

Neurons throughout the neocortex exhibit selective sensitivity to particular features of sensory input patterns. According to the prevailing views, cortical strategy is to choose features that exhibit predictable relationship to their spatial and/or temporal context. Such contextually predictable features likely make explicit the causal factors operating in the environment and thus they are likely to have perceptual/behavioral utility. The known details of functional architecture of cortical columns suggest that cortical extraction of such features is a modular nonlinear operation, in which the input layer, layer 4, performs initial nonlinear input transform generating proto-features, followed by their linear integration into output features by the basal dendrites of pyramidal cells in the upper layers. Tuning of pyramidal cells to contextually predictable features is guided by the contextual inputs their apical dendrites receive from other cortical columns via long-range horizontal or feedback connections. Our implementation of this strategy in a model of prototypical V1 cortical column, trained on natural images, reveals the presence of a limited number of contextually predictable orthogonal basis features in the image patterns appearing in the column’s receptive field. Upper-layer cells generate an overcomplete Hadamard-like representation of these basis features: i.e., each cell carries information about all basis features, but with each basis feature contributing either positively or negatively in the pattern unique to that cell. In tuning selectively to contextually predictable features, upper layers perform selective filtering of the information they receive from layer 4, emphasizing information about orderly aspects of the sensed environment and downplaying local, likely to be insignificant or distracting, information. Altogether, the upper-layer output preserves fine discrimination capabilities while acquiring novel higher-order categorization abilities to cluster together input patterns that are different but, in some way, environmentally related. We find that to be fully effective, our feature tuning operation requires collective participation of cells across 7 minicolumns, together making up a functionally defined 150 μm diameter “mesocolumn.” Similarly to real V1 cortex, 80% of model upper-layer cells acquire complex-cell receptive field properties while 20% acquire simple-cell properties. Overall, the design of the model and its emergent properties are fully consistent with the known properties of cortical organization. Thus, in conclusion, our feature-extracting circuit might capture the core operation performed by cortical columns in their feedforward extraction of perceptually and behaviorally significant information.