Biology subjects

Rajan, R.

Publications and source records attributed to Rajan, R..

At least 19 recordsLinked to original sources

bioRxiv2026

Plasma Extracellular Vesicle Lipidomics Reveals an SMPD1-Driven Sphingomyelin Salvage Pathway Collapse in Parkinson's Disease

While lysosomal lipid dysregulation is implicated in Parkinsons disease (PD), identifying the precise enzymatic drivers remains limited by the lack of subcellularly resolved metabolic mapping. Leveraging endosome-origin plasma extracellular vesicle (PsEV) lipidomics, we identified a profound bidirectional disruption of the ceramide-sphingomyelin (SM) axis in PD, driven by asymmetric upregulation of sphingomyelin phosphodiesterase 1 (SMPD1) and sphingomyelin synthase 1 (SGMS1). BODIPY-C5 SM tracking revealed that SMPD1 perturbation severely impairs lysosomal SM turnover. Crucially, this SMPD1-driven hydrolysis forces a salvage pathway collapse, bottlenecked by SPHK1/SGPL1 downregulation, which precipitates oxidative membrane damage and PINK1/Parkin-dependent mitophagy failure. We robustly validated this multi-pathway dysfunction across orthogonal in vitro, in vivo mouse, and postmortem human brain models. Furthermore, SMPD1/SGMS1 expression distinctly stratifies clinical phenotypes, marking the aggressive Postural Instability/Gait Difficulty (PIGD) subtype. Our findings establish SMPD1-mediated lysosomal impairment and ceramide-SM imbalance as a core biochemical axis in PD pathophysiology.

neuroscience↗

bioRxiv2026

Deep Brain Stimulation Microelectrodes as a Source of Human Subcortical RNA: Validation of a Low-Input Transcriptomic Protocol

BackgroundUnderstanding the molecular basis of Parkinsons disease (PD) phenotypic heterogeneity maybe improved by in vivo access to deep brain tissue. Deep brain stimulation (DBS) surgery offers a unique opportunity: microelectrodes traversing the subthalamic nucleus (STN) carry adherent brain tissue upon withdrawal, providing a source of RNA from subcortical regions in living patients without additional invasive procedures. AimTo develop and validate a low-input RNA extraction and transcriptomic profiling protocol using DBS microelectrodes in post-mortem human brain, to confirm that recovered RNA is of brain rather than blood origin, and to characterise its sub-regional and cellular identity. MethodologyDBS microelectrodes were inserted without image guidance or guide tube into three unfixed post-mortem human brains targeting the STN trajectory. In clinical practice, a guide tube shields the electrode from cortical tissue; its absence here means tissue from the full insertion trajectory may contribute to recovered RNA. Thirty-eight microelectrodes were evaluated across single and pooled strategies. RNA was extracted using a modified RNeasy Micro low-input protocol; libraries prepared using NEBNext Single Cell/Low Input RNA Library Kit and sequenced on Illumina NovaSeq 6000 (paired-end, 2x150 bp). Tissue identity was validated against GTEx v10 (54 tissues) and Allen Human Brain Atlas (ABA, 19 subcortical regions including STN) using Pearson correlation with permutation testing (1,000 permutations) and BH-FDR correction. Transcriptional overlap between subcortical and cortical reference regions was quantified and subcortical-enriched gene filtering performed. ResultsTwenty-five RNA isolates were obtained from 38 microelectrodes; 54.5% of Bioanalyzer-assessed samples achieved RIN [≥]5 (median 7.1; range: 5.9-7.8). Fifteen libraries passed sequencing QC (mean depth 43.0 {+/-} 14.1 million read pairs; mean Q30 83.2 {+/-} 5.6 %). PCA of rlog transformed expression data resolved samples by donor identity. All samples confirmed brain tissue origin by GTEx {tau}-index tissue specificity correlation (n=996 brain and blood specific markers). Brain correlations were highest for frontal cortex (mean r= 0.683 {+/-} 0.072), anterior cingulate cortex (mean r= 0.658 {+/-} 0.069), amygdala (mean r= 0.615 {+/-} 0.068), and basal ganglia including caudate (mean r= 0.553 {+/-} 0.059), putamen (mean r= 0.546 {+/-} 0.059), and nucleus accumbens (mean r= 0.544 {+/-} 0.057); all BH-FDR < 0.05. Cerebellum showed the lowest brain correlations (cerebellar hemisphere: mean r = 0.327 {+/-} 0.039; cerebellum: mean r = 0.314 {+/-} 0.037). Whole blood correlation was strongly negative (mean r= -0.250 {+/-} 0.079), confirming non-haematological origin. ABA genome-wide analysis confirmed positive STN correlation (r=0.54-0.62; permutation p<0.001). MuSiC cell-type deconvolution against the Allen Brain Atlas HMBA-BG snRNA-seq reference identified oligodendrocytes (33.5 {+/-} 17.2%), frontal cortical neurons (9.1 {+/-} 7.0%), STR D1 MSNs (6.0 {+/-} 4.9%), and dopaminergic neurons (1.1{+/-} 2.7%) as the principal cell types, independently corroborating bulk transcriptomic findings at single-cell resolution. ConclusionThis study validates a low-input RNA extraction protocol for DBS microelectrodes, confirming brain-specific transcriptomic profiles consistent with STN-adjacent subcortical sampling. The 96% transcriptional overlap between cortical and subcortical regions, combined with absence of a guide tube in this post-mortem model, limits sub-regional specificity; clinical application with a guide tube would enrich the subcortical signal. These findings provide the methodological framework for in vivo molecular profiling of the human basal ganglia during DBS surgery in PD patients.

genetics↗

bioRxiv2025

Introductory notes before zebra finch song have unique timing properties while sharing acoustic properties with song

Preparatory neural activity precedes the initiation of simple movements and a key feature of this preparatory activity is its trial-by-trial correlation with features of the upcoming movement. Recent studies in the zebra finch, a songbird with a complex, naturally learned, movement sequence (song), have suggested that the repeats of short introductory notes (INs) at the start of each song bout, reflect motor preparation. However, whether IN properties correlate with upcoming song features remains poorly understood. Here, we addressed this question by recording and analyzing male zebra finch songs over a 3 year period. We found bout-to-bout correlations in the acoustic features of the last IN and the first song syllable. However, similar correlations were present between the first song syllable and the first IN and the first and second song syllable suggesting that INs are also part of the song sequence. Next, we found an age-related increase in the mean IN number before song and song tempo. If INs reflected preparation of song parameters, we expected age-related song changes to be predicted by IN-song correlations at a younger age. We did not find any such correlations. Finally, we compared INs to other repeated syllables within song and outside song bouts and found that the speeding up of intervals between successive INs is unique to INs. Overall our results showing similarities in the acoustic features of INs and song syllables suggest shared neural control of INs and song syllables, while differences in timing suggest different neural mechanisms controlling IN timing. Significance StatementSimple movements are believed to be "prepared" in the brain before execution and this preparatory neural activity is correlated with features of the upcoming movement. Recent studies have suggested that the short introductory notes before the complex song sequence of the zebra finch reflect motor preparation. Whether correlations exist for introductory notes and upcoming song remains poorly understood. Here we found bout-to-bout correlations between the acoustic properties of introductory notes and the first song syllable but our analyses suggest that this reflects shared neural control of the acoustics of both introductory notes and song syllables. We also found differences in the timing of introductory notes suggesting different neural mechanisms for controlling introductory note timing.

neuroscience↗

bioRxiv2025

Respiratory vocal coordination increases as zebra finches prepare to sing

Complex vocalizations like human speech and bird song require precise coordination between respiration and vocalizations with most vocalization being produced during the exhalation phase of respiration. However, when this coordination is established each time animals vocalize remains poorly understood. Here, we addressed this question by recording respiratory pressure in adult, male, zebra finches during singing. Zebra finches begin their song bouts by repeating a short vocalization called an introductory note (IN), before producing song and these INs have been hypothesized to reflect motor preparation for song. We found that each IN is associated with a large amplitude expiratory pulse. Birds that did not produce INs had a few silent, large amplitude, IN-like, expiratory pulses just before starting song. Expiratory pressure and inspiratory pressure increased with successive repeats of the IN (silent or vocalized). Further, for birds with INs, coordination between respiration and vocalization increased with vocalizations beginning earlier in the exhalation and ending later in the exhalation, such that more of the expiratory pulse was filled with the vocalizaton. Overall, these results show that respiratory vocal coordination improves with each repetition of the IN and suggest that INs reflect preparation that involves coordination of respiratory and vocal neural circuitry.

neuroscience↗

bioRxiv2025

Zebra finch introductory notes do not influence female response to song and juvenile song learning accuracy

Many songbirds begin their song bouts with introductory notes (INs). In some songbird species like rufous-sided towhees and white-crowned sparrows, INs are believed to function in communication, to alert conspecifics about song onset or as a signal for species identification, but it is unclear whether this function is conserved in other species. Here, we addressed this question using the zebra finch, a well-studied songbird. Male zebra finches begin their song bouts with several INs and the number of INs increases when males sing to females or juveniles, suggesting a possible role of INs in female song preference and/or juvenile song learning. To test these hypotheses, we first recorded and analyzed call responses of female zebra finches to playbacks of different song stimuli. Female zebra finches responded equally to songs with and without INs, even when songs were degraded or when background noise was present. Second, we examined song learning accuracy of juveniles and found that juveniles copied songs accurately from their fathers independent of the fathers number of INs. Overall, these results show that zebra finch INs do not influence female response to song or juvenile song learning and suggest that INs might have different functions in different songbird species.

animal behavior and cognition↗

bioRxiv2025

BioToken and BioFM - Biologically-Informed Tokenization Enables Accurate and Efficient Genomic Foundation Models

Genomic variation underlies human phenotypic diversity, disease susceptibility, and evolutionary adaptation. Although large-scale genomic sequencing has transformed our ability to map genetic variation, accurately modeling and interpreting this data remains a central challenge; while genomic foundation models (GFMs) are a promising approach, they suffer from fundamental limitations. Current GFMs typically treat DNA simplistically as nucleotide-only sequences, overlooking critical biological context, such as genomic annotations, regulatory elements, and functional contexts central to genomic interpretation. Here, we introduce BioToken, a modular and extendable tokenization framework designed to encode genomic variants and biologically relevant region annotations directly into genomic representations. By utilizing intrinsic inductive biases, BioToken facilitates meaningful representation learning and generalization across diverse molecular phenotypes, such as gene expression, alternative splicing, and variant pathogenicity prediction. Built on BioToken, our genomic foundation model, BioFM, achieves competitive or superior results relative to specialized models (e.g., Enformer, SpliceTransformer) and GFMs up to 7B parameters across a comprehensive suite of genomic benchmarks, including noncoding pathogenicity, expression modulation, sQTL prediction, and long-range genomic interactions. Notably, BioFM achieves state-of-the-art performance with significantly fewer parameters (265M), substantially reducing training costs and computational requirements. Our findings highlight the substantial advantages of integrating biologically-informed inductive biases into genomic foundation modeling, providing a robust and accessible path forward in genomics. We provide our code and model checkpoints to support further research in this direction.

genomics↗

bioRxiv2025

Helical transition of the bridge helix of Cas12a is an allosteric regulator of R-loop formation and RuvC activation

CRISPR-Cas12a is widely used for genome editing and biomarker detection since it can create targeted double-stranded DNA breaks and promote non-specific DNA cleavage after identifying specific DNA. To mitigate the off-target DNA cleavage of Cas12a, we previously developed a Francisella novicida Cas12a variant (FnoCas12aKD2P) by introducing double proline substitutions (K969P/D970P) in a conserved helix called the bridge helix (BH). In this work, we used cryogenic electron microscopy (cryoEM) to understand the molecular mechanisms of BH-mediated activation of Cas12a. We captured five structures of FnoCas12aKD2P at different states of conformational activation. Comparison with wild-type (FnoCas12aWT) structures unravels a mechanism where BH acts as a trigger that allosterically activates REC lobe movements by tracking the number of base pairs in the growing RNA-DNA hybrid to undergo a loop-to-helical transition and bending to latch onto the hybrid. The transition of the BH is coupled to the previously reported loop-to-helix transition of the "lid", essential for opening RuvC endonuclease, through direct interactions of residues of the BH and the lid. We also observe structural details of cooperativity of BH and "helix-1" of RuvC for activation, a previously proposed interaction. Overall, our study enables development of high-fidelity Cas12a and Cas9 variants by BH-modifications.

biochemistry↗

bioRxiv2024

Molecular flexibility of high molecular weight hyaluronic acid measured by NMR has a profound effect on invasion of cancer cells

Extracellular hyaluronic acid (HA) has been shown to be important in cancer; low molecular weight HA typically correlates with cancer progression, high molecular weight HA with homeostasis. Here we show that even high molecular weight HA can induce cancer cell migration when it is highly diluted. HA-induced cell signalling is primarily through HA binding to the cell surface receptor, CD44. We show by NMR spectroscopy that at high dilution, high molecular weight HA molecules access the conformations needed for strong binding to CD44 on the tens of nanosecond timescale, the relevant timescale for induction of CD44 signalling. We further show that, in contrast, at higher concentrations, HA molecules have insufficient flexibility for strong CD44 binding. The high dilution HA condition correlates with profound changes in brain cancer cell morphology and proteome which supports cancer cell invasion. We hypothesize that the flexibility of HA molecules is central to HA-mediated cell signalling and that this concept can explain previous observations that the outcome of HA-mediated signalling depends on the HA molecular weight. HA dilution leading to stronger HA signalling may be important in understanding the role that oedema plays in cancer recurrence after primary surgery.

cancer biology↗

bioRxiv2024

Genomic Foundationless Models: Pretraining Does Not Promise Performance

AO_SCPLOWBSTRACTC_SCPLOWThe success of Large Language Models has inspired the development of Genomic Foundation Models (GFMs) through similar pretraining techniques. However, the relationship between pretraining performance and effectiveness in downstream genomic tasks remains unclear. Additionally, the high computational cost of pretraining raises questions about its cost-efficiency. To assess the usefulness of pretraining in genomics, we evaluated seven different GFMs across 52 diverse genomic tasks, comparing them to their counterparts with randomly initialized weights. Across benchmarks, we find that randomly initialized models provide surprisingly strong baselines and tokenizer and architecture choices strongly shape both these baselines and the gains from pretraining. Specifically, character-token models often match or exceed the performance of larger pretrained k-mer or BPE models, whereas subword models appear to benefit from pretraining. We also find that the evaluated GFMs fail to capture clinically relevant genetic mutations, with embeddings and log-likelihood ratios showing limited sensitivity to annotated variants. For the tasks we study, these results suggest that current NLP-style pretraining strategies provide modest, tokenizer-gated improvements over strong random baselines and motivate more biologically informed tokenization and variant-aware objectives. Our code is available at github.com/m42-health/gfm-random-eval.

genomics↗

bioRxiv2022

CineFinch: An animated female zebra finch for studying courtship interactions

Dummies, videos and computer animations have been used extensively in animal behaviour to study simple social interactions. These methods allow complete control of one interacting animal, making it possible to test hypotheses about the significance and relevance of different elements of animal displays. Recent studies have demonstrated the potential of videos and interactive displays for studying more complex courtship interactions in the zebra finch, a well-studied songbird. Here, we extended these techniques by developing an animated female zebra finch and showed that ~40% of male zebra finches (n=5/12) sing to this animation. To study real-time social interactions, we developed two possible methods for closed loop control of animations; (1) an arduino based system to initiate videos/animations based on perch hops and (2) a video game engine based system to change animations. Overall, our results provide an important tool for understanding the dynamics of complex social interactions during courtship. SUMMARY STATEMENTWe develop and test an animation of a female zebra finch to study song and courtship interactions in the male zebra finch.

animal behavior and cognition↗

bioRxiv2022

Visual experience instructs the organization of cortical feedback inputs to primary visual cortex.

Cortical feedback (FB) projections are thought to modulate lower-order activity depending on learned expectations. However, whether FB inputs become bound to specific lower-order neurons depending on experience is unknown. We measured the effects of dark rearing and manipulations of experienced visual statistics on the retinotopic specificity of projections from the lateromedial (LM) visual area to layer 1 of the mouse primary visual cortex (V1). LM inputs were, on average, retinotopically matched with V1 neurons irrespective of visual experience. While the orientation tuning of LM axons determined the retinotopic position of the V1 neurons they innervated, this organization was absent in dark-reared mice. Restricting visual experience to a narrow range of orientations revealed that visual experience exerts an instructive role in the retinotopic organization of LM inputs in V1. Our observations support theories of hierarchical computation proposing that inputs from higher-order neurons to lower-order ones reflect learned hierarchical associations.

neuroscience↗

bioRxiv2022

Psychophysiological stress induced neurobehavioral changes in adolescent rat and their impact in Adult rat enhanced by cinnamaldehyde

Adolescent is a tricky developmental period were the Physical, cognitive and social changes takes place. Adolescent brain undergoes vigorous maturation and more susceptible to stressors, distresses in the brain development leading to more susceptibility for stress related psychophysiological disorders in later life. The present study explores the association of adolescent stress on same period and on adult. Adolescent rats were restraint to induce psychophysiological stress from PND28 to PND42.Cinnamaldehyde (CA) 25 mg/kg body weight is treated along with the stress. Restraint stress showed more deleterious effect on learning, memory, anxiety, depression and locomotor activity. The result of this study reveal that adolescent stress has impact on that period and even long-lasting impact. But CA may act as antistressor and cognitive enhancer.

animal behavior and cognition↗

bioRxiv2021

E-cadherin regulates the stability and transcriptional activity of β-catenin in embryonic stem cells

E-CADHERIN is abundantly expressed in embryonic stem cells (ESCs) and plays an important role in the maintenance of cell-cell adhesions. However, the exact function of this molecule beyond cell adhesion, in the context of cell fate decisions is largely unknown. Using mouse ESCs (mESCs), we demonstrate that E-CADHERIN and {beta}- CATENIN interact at the membrane and continue to do so upon internalization within the cell. Knockout of the gene encoding E-CADHERIN, Cdh1, in mESCs resulted in a failure to form tight colonies, accompanied by altered expression of differentiation markers, and retention of pluripotency factor expression during differentiation. Interestingly, Cdh1-/- mESCs showed a dramatic reduction in {beta}-CATENIN levels. Transcriptional profiling of Cdh1-/- mESCs displayed a significant alteration in the expression of a subset of {beta}-CATENIN targets, in a cell-state dependent manner. While treatment with a pharmacological inhibitor against GSK3{beta} could rescue levels of {beta}-CATENIN in Cdh1-/- mESCs, expression of downstream targets were altered in a context-dependent manner, indicating an additional layer of regulation within this subset. Together, our results reveal the existence of a cell-state-dependent regulation of {beta}-CATENIN and its transcriptional targets in an E-CADHERIN dependent manner. Our findings hint at hitherto unknown roles played by E- CADHERIN in regulating the activity of {beta}-CATENIN in ESCs. Significance StatementAre cell adhesions only responsible for maintaining tissue architecture, or do they also regulate cell fate decisions during early embryonic stages by modulating the output of specific signalling pathways? In this study, we study the role of E- CADHERIN, a crucial component of cell-cell adhesions in the context of mouse embryonic stem cells (mESCs). We find that E-CADHERIN regulates the stability and activity of {beta}-CATENIN in mESCs through physical interactions. However, the loss of E-CADHERIN affected the expression of only a subset of downstream targets of {beta}-CATENIN in a cell-state dependent manner. This study highlights a critical cross-talk between molecules involved in cell-cell adhesion and the underlying signalling network critical for establishing cell fate during early mammalian development.

cell biology↗

bioRxiv2020

Somatosensory Cortex of Macaque Monkeys is Designed for Opposable Thumb

The evolution of opposable thumb has enabled fine grasping ability and precision grip, which led to the capacity for fine manipulation of objects and refined tool use. Since tactile inputs to an opposable thumb are often spatially and temporally out of synch with inputs from the fingers, we hypothesized that inputs from the opposable thumb would be processed in an independent module in the primary somatosensory cortex (area 3b). Here we show that in area 3b of macaque monkeys, most neurons in the thumb representation do not respond to tactile stimulation of other digits and receive few intrinsic cortical inputs from other digits. However, neurons in the representations of other digits respond to touch on any of the four digits and are significantly more interconnected in the cortex. The thumb inputs are thus processed in an independent module, whereas there is significantly more inter-digital information exchange between the other digits. This cortical organization reflects behavioral use of the hand with an opposable thumb.

neuroscience↗

bioRxiv2020

Nest records, Nest Site selection of Gyps bengalensis White-rumped Vulture and the role of Feeding Station in Kangra, Himachal Pradesh

Active nests of Gyps bengalensis White-rumped Vulture depends on elevation and aspects for nest site selection, while feeding station plays a significant role for determining the position of the nesting sites.This study attempted to record nest count for the breeding period 2018, identify key variables for the nest site selection and understand the role of feeding station in the nest site selection. Nest counts were conducted during the breeding period, each nest was categorized into active and inactive nest based on assesment of different components. Simultaneously, different variables (tree height, tree species, elevation and aspect) were recorded for each nest. Aerial distance was used to determine the role of feeding station for selecting the nesting sites. From the 24 nesting sites, 352 active nests were recorded, and a significant Pearsons correlation for elevation and aspect were drawn. We found, vulture prefer single tree species for nesting. We also found that, 71% (n = 17) nesting sites located within radial distance of 20 km of the feeding station. High congregration of active nests within short radial distance from feeding station, signify the positive impact of management of feeding station by the wildlife wing of Forest department since 2008, for the ex-situ conservation of critically endangered Gyps bengalensis White-rumped Vulture

ecology↗

bioRxiv2020

Introductory gestures before songbird vocal displays are shaped by learning and biological predispositions

Introductory gestures are present at the beginning of many animal displays. For example, lizards start their head-bobbing displays with introductory push-ups and animal vocal displays begin with introductory notes. Songbirds also begin their vocal displays by repeating introductory notes (INs) before producing their learned song and these INs are thought to reflect motor preparation. Between individuals of a given species, the acoustic structure of INs and the number of times INs are repeated before song varies considerably. While similar variation in songs between individuals is known to be a result of learning, whether INs are also learned remains poorly understood. Here, using natural and experimental tutoring with male zebra finches, we show that mean IN number and IN acoustic structure are learned from a tutor, independent of song learning. We also reveal biological predispositions in IN production; birds artificially tutored with songs lacking INs still repeated a short-duration syllable, thrice on average, before their songs. Overall, these results show that INs, just like elements in song, are shaped both by learning and biological predispositions and suggest multiple, independent, learning processes underlying the acquisition of complex vocal displays.

animal behavior and cognition↗

bioRxiv2019

Sensory feedback independent pre-song vocalizations correlate with current state of motor preparation

Many self-initiated, learned, motor sequences begin by repeating a simple movement, like ball-bouncing before a tennis serve, and this repetition is thought to represent motor preparation. Do these simple movements provide real-time sensory feedback used by the brain for getting ready or do they simply reflect internal neural preparatory processes? Here, we addressed this question by examining the introductory notes (INs) that zebra finches repeat before starting their learned song sequence. INs progress from a variable initial state to a stereotyped final state before each song and are thought to represent motor preparation before song. Here, we found that the mean number of INs before song and the progression of INs to song were not affected by removal of two sensory feedback pathways (auditory and proprioceptive). In both feedback-intact and feedback-deprived birds, the presence of calls (other non-song vocalizations), just before the first IN, was correlated with fewer INs before song and an initial state closer to song. Finally, the initial IN state correlated with the time to song initiation. Overall, these results show that INs do not provide real-time sensory feedback for preparing the motor system. Rather, repetition of INs, and possibly, other such simple movements, may reflect the \"current\" state of internal neural preparatory processes involved in getting the brain ready to initiate a learned movement sequence.\n\nSUMMARY STATEMENTThe number and progression of introductory notes to song in the zebra finch are not affected by removal of sensory feedback.

neuroscience↗

bioRxiv2018

Unidirectional monosynaptic connections from auditory areas to the primary visual cortex in the marmoset monkey

Until the late 20th Century, it was believed that different sensory modalities were processed by largely independent pathways in the primate cortex, with cross-modal integration only occurring in specialized polysensory areas. This model was challenged by the finding that the peripheral representation of the primary visual cortex (V1) receives monosynaptic connections from areas of the auditory cortex in the macaque. However, auditory projections to V1 have not been reported in other primates. We investigated the existence of direct interconnections between V1 and auditory areas in the marmoset, a New World monkey. Labelled neurons in auditory cortex were observed following 4 out of 10 retrograde tracer injections involving V1. These projections to V1 originated in the caudal subdivisions of auditory cortex (primary auditory cortex, caudal belt and parabelt areas), and targeted parts of V1 that represent parafoveal and peripheral vision. Injections near the representation of the vertical meridian of the visual field labelled few or no cells in auditory cortex. We also placed 8 retrograde tracer injections involving core, belt and parabelt auditory areas, none of which revealed direct projections from V1. These results confirm the existence of a direct, nonreciprocal projection from auditory areas to V1 in a different primate species, which has evolved separately from the macaque for over 30 million years. The essential similarity of these observations between marmoset and macaque indicate that early-stage audiovisual integration is a shared characteristic of primate sensory processing.

neuroscience↗