Biology subjects

Montaldo, G.

Publications and source records attributed to Montaldo, G..

11 recordsLinked to original sources

bioRxiv2026

Cooperative processing of visual threat across collicular pathways

Rapid defensive actions require the transformation of sensory cues into appropriate motor responses. The superior colliculus is central to this transformation, containing defined cell-types that form parallel output pathways linking visual inputs to distinct behaviors. However, whether these pathways act independently or cooperate remains unclear. Here we combine cell-type-specific inhibition, large-scale electrophysiology, and functional ultrasound imaging to determine how these pathways contribute to visually evoked defensive behaviors. Inhibiting either narrow-field or wide-field neurons impaired escape to overhead visual threats, demonstrating that both pathways contribute to escape. Recordings from downstream targets revealed a compact representation in the deeper layers of the superior colliculus that selectively distinguished visual stimuli associated with escape, whereas the lateral posterior thalamus contained a broader representation of visual stimuli. The representation of visual threat in the deeper layers of the superior colliculus predicted escape initiation and vigor in freely moving animals. Across the brain, functional ultrasound imaging showed that visual stimuli recruited distinct patterns of activity that could not be explained by response magnitude alone or by the contribution of single cell-types. Together, these results reveal a cooperative circuit architecture in which parallel pathways carry distinct but complementary signals that jointly support visually evoked escape.

neuroscience↗

bioRxiv2026

Volumetric functional ultrasound imaging in macaques

Linking circuit level activity to large scale functional organization requires imaging methods combining high spatial resolution, broad coverage, and single trial sensitivity. We present volumetric functional ultrasound imaging (3D-fUS) in behaving macaques, enabling imaging of ~1 cm3 cortical volumes at high spatiotemporal resolution (100 x 150 x 150 m3 voxels, 1.67 Hz). Visually evoked responses were reliably detected at the level of single trials and single voxels, substantially reducing experimental time. To enable model-based analyses analogous to functional magnetic resonance imaging (fMRI), we estimated a canonical fUS hemodynamic response function (fUS-HRF) that was consistent across subjects, cortical areas, and visual stimuli and was well approximated by a gamma function. Compared with canonical fMRI HRFs, the fUS-HRF exhibited faster dynamics, enabling shorter and more closely spaced stimulus presentations. Together, these results establish 3D-fUS as a fast, volumetric, and circuit relevant imaging modality for efficient investigation of distributed cortical dynamics in primates.

neuroscience↗

bioRxiv2025

OfUSA: OpenfUS Analyzer, a versatile open-source framework for the analysis and visualization of functional ultrasound imaging data across animal models

Functional ultrasound (fUS) imaging is rapidly gaining interest for its unprecedented ability to study large-scale brain dynamics, yet its adoption and broader dissemination have been hindered by the lack of standardized tools and methodologies to analyze and interpret its rich datasets. We present OpenfUS Analyzer (OfUSA), a companion software suite designed to help researchers quickly engage with fUS data and perform the full range of analyses needed to generate publication-ready results and figures without relying on additional software. OfUSA offers a versatile and modular architecture including preprocessing, recording quality assessment, signal dynamics exploration, statistical analysis and visualization. These functions are separated yet easily combined into analytic pipelines through a programming-free graphical interface. The framework can be applied across species and experimental contexts, either by registering data to anatomical atlases, as shown here for the mouse brain, or by analyzing data without atlas constraints, as illustrated in a primate dataset. This flexibility, together with its comprehensive functionality, makes OfUSA a practical solution for standardized and reproducible analysis of fUS data in both preclinical and translational research. Using OfUSA, we demonstrate the capacity to detect stimulus-evoked responses with high sensitivity, identify their spatial localization within brain networks, and quantify both their extent and temporal dynamics. These results highlight the softwares ability to capture robust activation patterns and provide detailed insights into brain function, thereby accelerating the use of fUS as a powerful tool for systems neuroscience. HighlightsWe present OpenfUS Analyzer (OfUSA), a novel software platform for the complete analysis of functional ultrasound (fUS) datasets. OfUSA combines a user-friendly graphical interface with a standardized, flexible workflow and powerful visualization tools, making it an ideal solution for fUS researchers at all experience levels. The softwares utility is first demonstrated through the analysis of rodent fUS data using a standardized atlas, while its versatility is further emphasized by the successful analysis of a primate fUS dataset without a template, thereby illustrating its adaptability to non-standard experimental conditions.

neuroscience↗

bioRxiv2025

Continuous monitoring of cerebrovascular autoregulation using functional ultrasound imaging in the piglet brain.

Continuous real-time assessment of cerebral blood flow (CBF) and cerebrovascular autoregulation (CA) remains a major unmet clinical need in acute brain injury. Methods such as laser Doppler flowmetry (LDF), transcranial Doppler, or indirect indices lack accuracy and robustness. Functional ultrasound (fUS) is an emerging modality combining high spatiotemporal resolution, large field-of-view, and sensitivity to blood velocity and volume, making it a promising neuromonitoring tool. Piglets were equipped with arterial blood pressure (ABP), intracranial pressure (ICP), and LDF probes, plus cranial windows for fUS and red blood cell (RBC) flux imaging. CA was challenged by non-pharmacological ABP manipulation via intraaortic or intracaval balloon inflation. fUS hemodynamic parameters were compared with other modaliters across a CPP range of 10-150 mmHg. fUS provided continuous, stable intensity- and velocity-derived parameters across vessels types. CBF estimates correlated strongly with RBC flux and showed reproducibility comparable to LDF, with lower inter-animal variability. Autoregulation breakpoints were reliably identified by fUS, particularly the lower limit, while the upper limit was more variable. Parcellation confirmed robustness of fUS across brain regions. fUS images CBF and CA with higher stability and reproducibility than standard approaches, supporting its applicability for bedside neuromonitoring and clinical translation.

neuroscience↗

bioRxiv2024

Functional ultrasound imaging and neuronal activity: how accurate is the spatiotemporal match?

Over the last decade, functional ultrasound (fUS) has risen as a critical tool in functional neuroimaging, leveraging hemodynamic changes to infer neural activity indirectly. Recent studies have established a strong correlation between neural spike rates (SR) and functional ultrasound signals. However, understanding their spatial distribution and variability across different brain areas is required to thoroughly interpret fUS signals. In this regard, we conducted simultaneous fUS imaging and Neuropixels recordings during stimulus-evoked activity in awake mice within three regions the visual pathway. Our findings indicate that the temporal dynamics of fUS and SR signals are linearly correlated, though the correlation coefficients vary among visual regions. Conversely, the spatial correlation between the two signals remains consistent across all regions with a spread of approximately 300 micrometers. Finally, we introduce a model that integrates the spatial and temporal components of the fUS signal, allowing for a more accurate interpretation of fUS images.

neuroscience↗

bioRxiv2023

Functional ultrasound imaging of stroke in awake rats

Anesthesia is a major confounding factor in preclinical stroke research as stroke rarely occurs in sedated patients. Moreover, anesthesia affects both brain functions and the stroke outcome acting as neurotoxic or protective agent. So far, no approaches were well suited to induce stroke while imaging hemodynamics along with simultaneous large-scale recording of brain functions in awake animals. For this reason, the first critical hours following the stroke insult and associated functional alteration remain poorly understood. Here, we present a strategy to investigate both stroke hemodynamics and stroke-induced functional alterations without the confounding effect of anesthesia, i.e., under awake condition. Functional ultrasound (fUS) imaging was used to continuously monitor variations in cerebral blood volume (CBV) in +65 brain regions/hemisphere for up to 3hrs after stroke onset. The focal cortical ischemia was induced using a chemo-thrombotic agent suited for permanent middle cerebral artery occlusion in awake rats, and followed by ipsi- and contralesional whiskers stimulation to investigate on the dynamic of the thalamo-cortical functions. Early (0-3hrs) and delayed (day 5) fUS recording enabled to characterize the features of the ischemia (location, CBV loss), spreading depolarizations (occurrence, amplitude) and functional alteration of the somatosensory thalamo-cortical circuits. Post-stroke thalamo-cortical functions were affected not only early after the stroke onset but were also altered secondarly and remotely from the initial insult. Overall, our procedure enables early, continuous, and chronic evaluations of hemodynamics and brain functions which, combined to stroke or other pathologies, aims to better understand physiopathologies toward the development of clinically relevant therapeutic strategies.

neuroscience↗

bioRxiv2022

Large scale in vivo acquisition, segmentation and 3D reconstruction of cortical vasculature using functional ultrasound imaging.

The brain is composed of a dense and ramified vascular network comprising various sizes of arteries, veins, and capillaries. One way to assess the risk of cerebrovascular pathologies is to use computational models to predict the physiological effects of a reduction of blood supply and correlate these responses with observations of brain damage. Therefore, it is crucial to establish a detailed 3D organization of the brain vasculature, which could be used to develop more accurate in silico models. For this purpose, we have adapted our open-access functional ultrasound imaging platform previously designed for recording brain-wide activity that is now capable of fast and reproducible acquisition, segmentation, and reconstruction of the cortical vasculature. For the first time, it allows us to digitize the cortical vasculature in awake rodents with a [~]100 {micro}m3 spatial resolution. Contrary to most available strategies, our approach can be performed in vivo within minutes. Moreover, it is easy to implement since it neither requires exogenous contrast agents nor long post-processing time. Hence, we performed a cortex-wide reconstruction of the vasculature and its quantitative analysis, including i) classification of descending arteries versus ascending veins in more than 1500 vessels/animal, ii) quick estimation of their length. Importantly, we confirmed the relevance of our approach in a model of cortical stroke, which enables quick visualization of the ischemic lesion. This development contributes to extending the capabilities of ultrasound neuroimaging to understand better cerebrovascular pathologies such as stroke, vascular cognitive impairment, and brain tumors and is highly scalable for the clinic.

neuroscience↗

bioRxiv2022

Brain-wide continuous functional ultrasound imaging for real-time monitoring of hemodynamics during ischemic stroke

Ischemic stroke occurs with no warning, and therefore, very little is known about hemodynamic perturbations in the brain immediately after stroke onset. Here, functional ultrasound imaging was used to monitor variations in relative cerebral blood volume (rCBV) compared to baseline. rCBV levels were analyzed brain-wide and continuously at high spatiotemporal resolution (100m, 2Hz) until 70mins after stroke onset in rats. We compared two stroke models, with either a permanent occlusion of the middle cerebral artery (MCAo) or a tandem occlusion of both the common carotid and middle cerebral arteries (CCAo+MCAo). We observed a typical hemodynamic pattern, including a quick drop of the rCBV after MCAo, followed by spontaneous reperfusion of several brain regions located in the vicinity of the ischemic core. The severity and location of the ischemia were highly variable between animals. Still, both parameters were, on average, in good agreement with the final ischemic lesion volume measured 24hrs after stroke onset for the MCAo but not the CCAo+MCAo model. For the latter, we observed that the infarct was extended to regions that were initially not ischemic and located rostrally of the ischemic core. These regions strongly colocalize with the origin of transient hemodynamic events associated with spreading depolarizations.

neuroscience↗

bioRxiv2021

Social-vocal brain networks in a non-human primate

During social interactions, individuals influence each other to coordinate their actions. Vocal communication is an exceptionally efficient way to exert such influence. Where and how social interactions are dynamically modulated in the brain is unknown. We used functional ultrasound imaging in marmoset monkeys - a highly vocal species - to investigate the dynamics of medial social brain areas in vocal perception, production, and audio-vocal interaction. We found that the activity of a distributed network of subcortical and cortical regions distinguishes calls associated with different social contexts. This same brain network showed different dynamics during externally and internally driven vocalizations. These findings suggest the existence of a social-vocal brain network in medial cortical and subcortical areas that is fundamental in social communication. One Sentence SummaryA network of medial subcortical and cortical brain areas gate social communication in primates.

neuroscience↗

bioRxiv2021

Neural basis of functional ultrasound signals

Functional ultrasound imaging (fUSI) is a popular method for measuring blood flow and thus infer brain activity, but it relies on the physiology of neurovascular coupling and requires extensive signal processing. To establish to what degree its trial-by-trial signals reflect neural activity, we performed simultaneous fUSI and neural recordings with Neuropixels probes in awake mice. fUSI signals strongly correlated with the slow (<0.3 Hz) fluctuations in local firing rate, and were closely predicted by the smoothed firing rate of local neurons, particularly putative inhibitory neurons. The optimal smoothing filter had width ~3 s, matched the hemodynamic response function of awake mouse, was invariant across mice and stimulus conditions, and similar in cortex and hippocampus. fUSI signals also matched neural firing spatially: firing rates were as highly correlated across hemispheres as fUSI signals. Thus, hemodynamic signals measured by ultrasound bear a simple and accurate relationship to neuronal firing.

neuroscience↗

bioRxiv2020

Brain-wide mapping of neural activity mediating collicular-dependent behaviors

Neuronal cell-types are arranged in brain-wide circuits to guide behavior. In mice, the superior colliculus is comprised of a set of cell-types that each innervate distinct downstream targets. Here we reveal the brain-wide networks downstream of four collicular cell-types by combining functional ultrasound imaging (fUSi) with optogenetics to monitor neural activity at a resolution of ~100 m. Each neuronal group triggered different behaviors, and activated distinct, partially overlapping sets of brain nuclei. This included regions not previously thought to mediate defensive behaviors, e.g. the posterior paralaminar nuclei of the thalamus (PPnT), that we show to play a role in suppressing habituation. Electrophysiological recordings support the fUSi findings and show that neurons in the downstream nuclei preferentially respond to innately threatening visual stimuli. This work provides insight into the functional organization of the networks governing defensive behaviors and demonstrates an experimental approach to explore the whole-brain neuronal activity downstream of targeted cell-types.

neuroscience↗