bioRxiv Subject Collection: Neuroscience's Journal

Early development of direction selectivity in higher visual cortex
A fundamental aspect of visual motion processing is the computation of motion direction. In ferrets, as in primates, selectivity for motion direction is found both in early cortical stages like the primary visual cortex (V1) and in higher visual areas like primate MT and ferret PMLS. Little is known about how this critical tuning function develops in higher visual cortex. Here, by studying the development of the ferret's motion pathway, we first reveal the surprising finding that direction selectivity develops earlier in PMLS than in V1, contrary to the areas' hierarchical positions. Our data furthermore show that while direction selectivity is sensitive to visual experience in both areas, the sensitivity profile differs between them: Moving stimuli, containing both spatial and temporal cues, are required to promote direction selectivity development in V1, but flashing stimuli that remain stationary spatially are sufficient for direction selectivity development in PMLS. Collectively, our findings reveal that the development of the motion pathway is highly complex when considered at the network level, and does not adhere to a simple feedforward model in which the development of lower visual areas sets the pace for higher ones. Not only will developmental models need to be updated to include this complexity, characterizing the link between the development of different visual areas will likely also be crucial for understanding the consequences of developmental disorders.

Multimodal cortical connectome in the default mode network across the adult lifespan
The default mode network (DMN) critically underpins cognitive and affective functions throughout the adult lifespan; however, detailed insights into its complex neuroarchitecture and connectivity patterns across aging remain limited. Leveraging the open-access CamCAN dataset, comprising structural and diffusion magnetic resonance imaging (MRI) alongside magnetoencephalography (MEG) data from 599 adults spanning ages 18 to 88 years, we systematically investigated age-associated changes in multimodal connectomes within the DMN. Our analyses revealed a progressive decline in both structural and functional connectivity among DMN subregions with advancing age. Additionally, MEG-based connectivity assessment demonstrated age-related decreases in high-frequency oscillatory activity (alpha, beta, gamma bands) accompanied by increases in low-frequency oscillations (theta band). Integrating structural data with neurophysiological measures further revealed age-dependent shifts in neurophysiological-structural coupling within the prefrontal cortex, characterized by strengthened coupling at theta frequencies but weakened coupling at higher frequencies. Conversely, coupling within the posterior cingulate cortex consistently declined across all examined frequency bands. Notably, theta-band coupling within the prefrontal cortex significantly correlated with age-related memory performance variations. Collectively, our findings delineate nuanced changes in DMN information transmission dynamics across adulthood, underscoring its promise as a neurobiological biomarker reflective of cognitive aging heterogeneity.

Impaired Complex I dysregulates neural/glial precursors and corpus callosum development revealing postnatal defects in Leigh Syndrome mice
Leigh syndrome (LS) is a complex, genetic mitochondrial disorder defined by neurodegenerative phenotypes with pediatric manifestation. However, recent clinical studies report behavioral phenotypes in human LS patients that are more reminiscent of neurodevelopmental delays. To determine if disruptions in epochs of rapid brain growth during infancy precede the hallmark brain lesions that arise during childhood, we evaluated neural and glial precursor cellular dynamics in a mouse model of LS. Single cell RNA sequencing along with histological and anatomical assessments were performed in NDUFS4 KO mice and compared with controls to determine the impact of Complex I deficiency on neural stem cells, their neuronal and oligodendroglial progeny, lineage progression, and overt differences in specific brain regions. Our findings show disruptions in all categories, specifically within the subventricular zone and corpus callosum. Given that LS is purely considered a neurodegenerative disease, we propose that mitochondrial dysfunction is a neurodevelopmental signature predating classic diagnosis in LS.

Geometric principles of dendritic integration of excitation and inhibition in cortical neurons
We use two-color uncaging of glutamate and gamma-aminobutyric acid (GABA) on layer-5 (L5) pyramidal neurons of the cingulate cortex to define how inhibitory control of excitation is controlled by dendritic geometry. Traditionally, GABAergic input was considered as the gatekeeper, thus, receptors closest to the soma were ideally placed to veto excitation. However, recently modeling has advanced several counter-intuitive hypotheses. Since laser uncaging can be directed at will to any position, we used photostimulation to show that inhibition near the sealed end of dendrites distal to excitation is more effective than inhibition near the soma in modulating excitation. Further, dendritic inhibition was found to be branch specific. Finally, we demonstrate that inhibitory input from multiple thin basal dendrites can centripetally elevate to effectively tune distant excitation at the soma. These findings provide direct experimental evidence supporting theoretical predictions based on dendritic cable properties, revealing the critical role of dendritic geometry in shaping the interaction between excitatory and inhibitory neurotransmission.

Basolateral amygdala dopamine transmits a nonassociative emotional salience signal
Adaptive decision making relies on proper discrimination and prediction of positive and negative events. The basolateral amygdala (BLA) is central to this valence encoding, assigning emotional value to stimuli to drive appropriate behavioral responses. The ventral tegmental area (VTA), which is classically known to regulate associative learning and incentive motivation via dopamine projections to the striatum, also contains strong dopamine projections to the BLA, but this system has received much less attention. Here, we used fiber photometry to investigate how in vivo BLA dopamine signaling tracks learning. We show that reward cues evoke BLA dopamine signals that diminish, rather than grow, with training. As the complexity of the learning context was increased, where rats actively differentiated between various cue types signaling threat, reward, safety, and neutral associations, the magnitude of cue-evoked BLA dopamine responses was largest early in training and reported the level of perceived emotional saliency. Fear and safety cues prompted larger, sustained dopamine signals compared to reward and neutral cues, an effect that was more apparent in female rats, compared to males. Together, our findings broaden the theoretical landscape of dopamine heterogeneity, showing that BLA dopamine supports dynamic disambiguation of relative stimulus importance by non-associatively encoding sensory state transitions, independent of value. These signals reflect a scalar readout of emotional salience to prime, rather than track, learning.

Neural signatures of predictive coding underlying the acquisition of incidental sensory associations
A longstanding question in cognitive science is whether the human brain learns sensory regularities that are irrelevant to ongoing behavior, a phenomenon known as incidental associative learning. Here, we provide evidence at the single subject level that humans indeed acquired such incidental associations and reveal their neural signatures by combining Electroencephalography (EEG), multivariate decoding and computational modeling. We found robust encoding of incidental predictions and prediction errors underlying associative learning, consistent with predictive coding theories. Prediction errors were modulated by epistemic uncertainty, incidental associations persisted in memory over days and generalized beyond stimulus-stimulus pairings to encompass broader sensory events, including the absence of stimulation. Together, our results challenge traditional assumptions that associative learning requires behavioral relevance or physical co-occurrence and point to uncertainty minimization about environmental state transitions as a general objective of brain function. This intrinsic drive may reflect a fundamental computational principle supporting the formation of internal predictive models that guide perception, learning, and adaptive behavior.

Visual Field Inhomogeneities Shape Visual Working Memory
It is a topic of scientific debate whether early visual cortex (V1) is essential for creating visual working memory (vWM) representations. The current study aimed to replicate and expand previous research regarding the role of structural properties of V1 in vWM retention. Structural properties of V1, particularly visual field inhomogeneities (including visual field and polar angle asymmetries), were investigated to link interindividual differences in vWM performance to V1 structural differences. 292 participants underwent the MRI scan with the multiparametric mapping sequence, resulting in four microstructural maps per participant: magnetization transfer (MT), proton density (PD), longitudinal relaxation rate (R1), and transverse relaxation rate (R2*). During a separate session, the participants performed the vWM task. Both visual field and polar angle asymmetries were present in our dataset. We replicated behavioral asymmetries in vWM shown in previous studies, particularly the inverted polarity of the vertical meridian asymmetry (VMA) and found a link between VMA and R2* values in V1. This suggests a potential role of cortical iron content in V1 for vWM, particularly along the vertical meridian of the visual field, supporting the sensory recruitment hypothesis, thus indicating that early visual areas are crucial for vWM retention.

Direct interoceptive input to the insular cortex shapes learned feeding behavior
The insular cortex (insula) is an interoceptive hub, which senses internal states such as hunger, thirst, pain, and emotions. Previous studies, however, suggest that the insula directly senses internal states, but the mechanisms remain elusive. We identified a novel population of glutamatergic leptin receptor-positive (LepR+) cells with a unique morphology in the insula (INSLepR). Based on leptin's known role in signaling adiposity levels, we hypothesized that INS-LepR neurons detect internal states and thus regulate food intake and body weight. Accordingly, we found that leptin administration in the insula increases intrinsic excitability of INSLepR cells, suppresses feeding, and reduces body weight. Moreover, optogenetic stimulation of INSLepR cells suppresses learned operant feeding and leads to avoidance in a real time place preference context. We also found that INSLepR neurons encode operant feeding bouts, and their activity is modulated specifically by hunger, but not thirst, states. Single-nuclei sequencing and ribosome profiling revealed that INSLepR is expressed on both Layer 6 neurons and on vascular cells, suggesting that leptin can be delivered directly through receptor-mediated transport through the blood brain barrier into the insula. . INSLepR neurons form mainly local connections within the insula and an external projection to the basolateral amygdala (BLA), and optogenetic stimulation of BLA terminals also regulated learned operant feeding. Moreover, we found that administration of leptin alters insula neural dynamics in response to feeding, but not drinking, behavior, and reshapes the transcriptome, suggesting that internal state information provided by leptin is used by the insula to coordinate feeding behavior. Taken together, our data supports a model for direct interoceptive input to the insula, in which INSLepR cells integrate adiposity level signals to regulate feeding and body weight in a learned manner.

Characterising the neural time-courses of food attribute representations
Dietary decisions involve the consideration of multiple, often conflicting, food attributes that precede the computation of an overall value for a food. The differences in the speed at which attributes are processed play an important role; however, it is unknown whether different attributes are processed over distinct time windows. We mapped the neural time-courses of 12 choice-relevant food attributes. Participants (N = 110) viewed food images while we recorded brain activity using electroencephalography (EEG). A separate group of participants (N = 421) rated the same images on nutritive properties (healthiness, calorie content, edibility, and level of transformation), hedonic properties (tastiness, willingness to eat, negative and positive valence, and arousal), and familiarity (previous exposure, recognisability, and typicality). Using representational similarity analysis, we quantified differences in patterns of multivariate EEG signals across foods and assessed whether the structure of these differences was correlated with differences in attribute ratings. We observed similar correlation time-courses for many attributes. There was an early window of correlations (~200 ms from image onset), followed by sustained windows of correlation from ~400-650 ms. Using principal components analysis, we identified a set of broader constructs that accounted for variance in ratings across multiple attributes, and also correlated with the EEG data. Our results indicate that food attributes important for choice are represented rapidly and in parallel, over similar time windows. Furthermore, we reveal that broad dimensions underlying individual attributes are also represented in the neural activity with distinct time-courses, indicating a multilevel structure of food attribute representations.

Inhibition of phosphodiesterase 4B as a novel therapeutic strategy for the treatment of refractory epilepsy
Despite the availability of nearly 40 approved anti-seizure medications (ASMs), at least one-third of individuals with epilepsy remain refractory to treatment, and many experience life-limiting cognitive or psychiatric side effects. Using a machine learning-guided platform, we identified PDE4 as an underexplored anti-seizure target, which became further validated based on its enriched expression in seizure-relevant brain regions and its potential to modulate excitatory/inhibitory neuronal tone via cAMP signaling. The pan-PDE4 inhibitor crisaborole partially protected against hyperthermia-induced seizures and reduced spontaneous seizures in Scn1a+/- mice, while rolipram and roflumilast showed no efficacy at tolerable doses. SN-2000, a first-in-kind allosteric modulator of PDE4B, was rationally designed for isoform selectivity and brain penetration, and demonstrated versatile reduction of seizure activity across multiple zebrafish and rodent genetic and acquired epilepsy models, with efficacy comparable to standard-of-care ASMs. SN-2000 also demonstrated favorable behavioral outcomes, reducing post-ictal aggression and anxiety-like behaviors, and improving cognitive performance in both wild-type and epileptic mice. These effects were linked to paradoxical regulation of excitatory and neuronal activity in the cortex and thalamus of epileptic mice, respectively, as well as elevated cAMP signaling and downstream pCREB activation. Together, these findings support PDE4B inhibition as a disease-relevant mechanism in epilepsy, and position SN-2000 as a promising therapeutic candidate offering seizure control without the neuropsychiatric burden of existing ASMs and potential pro-cognitive properties.

See-through science: Danionella cerebrum as a model for neuroregeneration
Rebuilding functional neuronal circuits after injury in the adult central nervous system (CNS) is unachievable for many vertebrates. In pro-regenerative models, it is unclear how regeneration and re-wiring is achieved in the CNS over long distances. The size and opacity of the adult vertebrate brain makes it difficult to study axon topography and dynamic cellular interactions during long-distance axon regeneration. Here, we harnessed the properties of the small and transparent adult Danionella cerebrum for longitudinal in vivo imaging of retinal ganglion cell axon regeneration, correlating cellular events with functional recovery. Our results suggest that some axons regenerate along tracts of degenerating myelin debris. However, the topography of re-innervation is different after regeneration, suggesting that new axon tracts are created to restore functional vision. The D. cerebrum model provides a unique opportunity to visualize and experimentally manipulate the spatial and temporal events during CNS regeneration in intact adult vertebrates.

Dibutyryl cyclic AMP downregulates tenascin-C in neurons and astrocytes and reduces AAV-mediated gene expression in DRG neurons
Functional recovery after spinal cord injury (SCI) is hindered by the limited ability of axons to regenerate in the adult mammalian central nervous system (CNS). Overcoming this barrier is critical for achieving effective recovery. Axonal regeneration depends on the activation of intracellular processes like transcription factor induction, protein and lipid trafficking, and cytoskeletal remodelling. Targeting these pathways offers a promising approach for promoting neuronal repair. This study examined the combined therapeutic effects of dibutyryl-cAMP (db-cAMP), which primes neurons for growth, and integrin 9 overexpression, which supports axonal extension. Using in vitro models with dorsal root ganglion (DRG) neurons and astrocytes, as well as an in vivo SCI model, we evaluated the potential of this approach. In vitro, the combination of db-cAMP and integrin 9 significantly enhanced neuronal growth. However, in vivo results were less consistent, with db-cAMP affecting AAV-mediated transcription and the expression of tenascin C (TnC) in neurons and astrocytes. These findings highlight the potential of modulating intracellular signalling and integrin activation but underscore the challenges posed by the complexity of the in vivo environment. Further studies are necessary to unravel these mechanisms and refine therapeutic strategies for effective SCI recovery.

Macrophage migration inhibitory factor is a potential therapeutic target for cisplatin induced peripheral neuropathy in breast cancer
Background: Cisplatin (CP) is an effective chemotherapy drug for several cancers. However, the use of CP is associated with peripheral neuropathy, a painful nerve disorder. Unfortunately, no therapies are available for CP-induced peripheral neuropathy (CisIPN). This study explored the role of a cytokine, the macrophage migration inhibitory factor (MIF), as a potential therapeutic target for CisIPN. Methods: The role of neuroinflammation and MIF in CisIPN was evaluated in mice models of CisIPN, with and without breast cancer, after treatment with the anti-inflammatory drug Dexamethasone (Dex). Circulating MIF levels in animals were examined using ELISA. Pharmacological inhibition of MIF was achieved using the small molecule inhibitors, CPSI-1306 and ISO-1. Mechanical and thermal sensitivities of animals were assessed using von frey filament and cold acetone assays. Macrophage infiltration in peripheral nerve tissues was examined using CD68 and Iba-1 staining. Results: Our results showed that Dex suppressed mechanical hyperalgesia in CisIPN animals, which was accompanied by downregulation of MIF. We also found that circulating MIF levels were increased in CisIPN animals. Furthermore, direct inhibition of MIF using CPSI-1306 and ISO-1 led to suppression of mechanical hyperalgesia, without compromising the anti-tumor efficacy of CP, in CisIPN animals. We did not find any significant change in macrophage infiltration in the peripheral nerve tissues of CisIPN animals. Immunostaining results indicated that sensory neurons in the DRGs and Schwann Cells in the sciatic nerves are potential sources for increased MIF in CisIPN. Interpretation: Overall, our results strongly suggest that MIF is a promising therapeutic target for CisIPN.

sKL/mKL Transcript Ratio and Protein Localization Define a Species- and Region-Specific Klotho Signature in the CNS and AD Progression
-Klotho is a multifunctional protein widely recognized for its anti-aging and neuroprotective properties. This study investigates the expression and localization of the secreted Klotho (s-KL) isoform in the human brain and its potential role in Alzheimer's disease. Using RT-qPCR, we observed that the s-KL transcript predominates over the membrane-bound KL (m-KL) in multiple brain regions, a pattern consistent in macaques and lemurs. Immunohistochemistry and immunoprecipitation assays confirmed the presence of the s-KL protein in human and mouse brain parenchyma, revealing species-specific cellular localization. In human cerebrospinal fluid (CSF), s-KL constitutes ~28% of total KL, with levels significantly reduced in mild dementia-AD patients. These findings underscore s-KL's potential neuroprotective role and highlight its differential regulation and expression during AD progression.

Pervasive homeobox gene function in the male-specific nervous system of Caenorhabditis elegans
We explore here how neuronal cell type diversity is genetically delineated in the context of the large, but poorly studied male-specific nervous system of the nematode Caenorhabditis elegans. Mostly during postembryonic development, the C. elegans male adds 93 male-specific neurons, falling into 25 cardinal classes, to the predominantly embryonically generated, sex-shared nervous system, comprised of 294 neurons (116 cardinal classes). Using engineered reporter alleles, we investigate here the expression pattern of 40 phylogenetically conserved homeodomain proteins within the male-specific nervous system of C. elegans, demonstrating that in aggregate, the expression of these homeodomain proteins covers each individual male-specific neuron. We show that the male-specific nervous system can be subdivided along the anterior/posterior axis in HOX cluster expression domains. The extent of our expression analysis predicts that each individual neuron class is likely defined by unique combinations of homeodomain proteins. Using a collection of newly available molecular markers, we undertake a mutant analysis of five of these genes (unc-30, unc-42, lim-6, lin-11, ttx-1) and identified defects in cell fate specification and/or male copulatory defects in each of these mutant strains. Our analysis expands our understanding of the importance of homeobox genes in nervous system development and function.

Volitional and forced running ability in mice lacking intact primary motor cortex
The coordination of various brain regions achieves both volitional and forced motor control, but the role of the primary motor cortex in proficient running motor control remains unclear. This study trained mice to run at high performance (>10,000 rotations per day or >2,700 rotations per hour) using a running wheel, and then assessed the effects of the removal of bilateral cortical areas including the primary motor cortex on volitional and forced running locomotion. The control sham-operated group revealed a quick recovery of volitional running, reaching half of the maximum daily rotation in 3.9 +/- 2.6 days (n = 10). In contrast, the cortical injury group took significantly a longer period (7.0 +/- 3.3 days, n = 15) to reach half of the maximum volitional daily rotation, but recovered to preoperative levels in about two weeks. Furthermore, even 3 days after surgery to remove cortical regions, the running time on a treadmill moving at 35.3 cm/sec, which is difficult for naive mice to run on, was not significantly different from that in the sham-operated group. These results suggest that the intact primary motor cortex is not necessarily required to execute trained fast-running locomotion, but rather contributes to the spontaneity of running in mice.

Hypoxia and Cognitive Ability in Humans: A Systematic Review and Meta-Analysis
This systematic and meta-analytical review examined how a reduction in oxygen availability to tissue (hypoxia) affects cognitive function. Hypoxia had a moderate-to-large detrimental effect on general cognitive ability and across domains, including memory, attention, executive function, processing speed, and psychomotor speed. Increased hypoxic severity was associated with greater declines in general cognitive ability and executive function, while longer duration of exposure was associated with greater declines in executive function and psychomotor speed. Participant age was a moderator for executive function and psychomotor speed, with older adults experiencing greater impairments. For executive function and psychomotor speed, the magnitude of these effects was less pronounced during intermittent and hypobaric exposures, potentially due to adaptive physiological mechanisms. While our models accounted for exposure characteristics and age of participants, substantial unexplained variance remained. These findings highlight hypoxias impact on cognition and emphasize the need to investigate underlying neurophysiological mechanisms that may influence individual vulnerability.

Global motor system suppression as the primary mechanism of human action stopping: challenging the pause-then-cancel model
The ability to stop a planned or ongoing action is fundamental to inhibitory control. A recent theory proposes that stopping involves two distinct phases: an initial global suppression of motor activity ("pause") followed by a selective cancellation of the targeted action. However, the necessity of a second "cancel" stage remains debated. We tested whether global suppression alone is sufficient to stop movement by analysing electromyography from task-relevant agonist and antagonist muscles, alongside transcranial magnetic stimulation measures of global motor suppression from task-irrelevant muscles, during a stop-signal task in adult human participants of both sexes. In Experiment 1, reanalysis of ballistic finger movements revealed that agonist muscle offset consistently preceded behavioural stopping, aligning with the time course of global suppression. In Experiment 2, we extended these findings to whole-arm reaching movements, demonstrating that global motor suppression persisted beyond the termination of muscle activity when stopping prevented movement initiation, but disengaged in time for antagonist activation used to interrupt movements once they had begun. These findings challenge the pause-then-cancel model, instead supporting a single-stage global suppression framework. They also suggest that the global suppression mechanism is not a rigid, top-down stopping mechanism but rather part of a broader motor control system that flexibly adjusts movement commands based on task demands.

The temporal and perceptual characteristics of emotion-induced blindness
Attentional capture by emotionally salient stimuli is adaptive, permitting identification of possible threats; however, an excessive bias towards emotional stimuli can interrupt goal-directed behavior. This is especially relevant in psychiatric disease, where severe emotional distress can interfere with daily function. As such, understanding the mechanisms by which emotional stimuli compete for attentional resources is a critical area of investigation. Previous studies using rapid serial visual presentation (RSVP) paradigms observe that emotional distractors disrupt the detection of subsequent stimuli, referred to as emotion-induced blindness (EIB). Our study expands upon this work, characterizing how temporal and perceptual factors shape the emergence and intensity of EIB. Contrary to previous assumptions regarding temporal dynamics of EIB, we found that effects of emotional distractors persisted across prolonged image presentation durations. Further, we investigated the extent to which the depth of distractor processing influences EIB using a distractor recall task. While recall was predictive of EIB magnitude, a significant effect of emotional distractors on target detection was nonetheless present even without conscious recall of the distractor. These findings demonstrate the robustness of the EIB effect in RSVP in the context of temporal and perceptual manipulations.