Biology subjects

Ortiz-Rios, M.

Publications and source records attributed to Ortiz-Rios, M..

4 recordsLinked to original sources

bioRxiv2021

Spatial signatures of anesthesia-induced burst-suppression differ between primates and rodents

During deep anesthesia, the electroencephalographic (EEG) signal of the brain alternates between bursts of activity and periods of relative silence (suppressions). The origin of burst-suppression and its distribution across the brain remain matters of debate. In this work, we used functional magnetic resonance imaging (fMRI) to map the brain areas involved in anesthesia-induced burst-suppression across four mammalian species: humans, long-tailed macaques, common marmosets, and rats. At first, we determined the fMRI signatures of burst-suppression in human EEG-fMRI data. Applying this method to animal fMRI datasets, we found distinct burst-suppression signatures in all species. The burst-suppression maps revealed a marked inter-species difference: in rats the entire neocortex engaged in burst-suppression, while in primates most sensory areas were excluded--predominantly the primary visual cortex. We anticipate that the identified species-specific fMRI signatures and whole-brain maps will guide future targeted studies investigating the cellular and molecular mechanisms of burst-suppression in unconscious states.

neuroscience↗

bioRxiv2021

Fusion of quantitative susceptibility maps and T1-weighted images improve braintissue contrast in primates

Recent progress in quantitative susceptibility mapping (QSM) has enabled the accurate delineation of submillimeter scale subcortical brain structures in humans. The simultaneous visualization of cortical, subcortical, and white matter structure remains, however, challenging, utilizing QSM data solely. Here we present TQ-SILiCON, a fusion method that enhances the contrast of cortical and subcortical structures and provides an excellent white matter delineation by combining QSM and conventional T1-weighted (T1w) images. In this study, we first applied QSM in the macaque monkey to map iron-rich subcortical structures. Implementing the same QSM acquisition and analysis methods allowed a similar accurate delineation of subcortical structures in humans. However, the QSM contrast of white and cortical gray matter was not sufficient for an appropriate segmentation. Applying automatic brain tissue segmentation to TQ-SILiCON images of the macaque improved the classification of subcortical brain structures as compared to the single T1 contrast by maintaining a good white to cortical gray matter contrast. Furthermore, we validated our dual-contrast fusion approach in humans and similarly demonstrated improvements in automated segmentation of cortical and subcortical structures. We believe the proposed contrast will facilitate translational studies in nonhuman primates to investigate the pathophysiology of neurodegenerative diseases that affect subcortical structures such as the basal ganglia in humans. HighlightsO_LIThe subcortical gray matter areas of macaque monkeys are reliably mapped by QSM, much as they are in humans. C_LIO_LICombining T1w and QSM images improves the visualization and segmentation of white matter, cortical and subcortical structures in the macaque monkey. C_LIO_LIThe proposed dual contrast TQ-SILiCON provides a similar image quality also in humans. C_LIO_LITQ-SILiCON facilitates comparative and translational neuroscience studies investigating subcortical structures. C_LI

neuroscience↗

bioRxiv2021

Optogenetic stimulation of primate V1 reveals local laminar and large-scale cortical networks related to perceptual phosphenes

Developing optogenetics in non-human primates (NHPs) is essential for translating its successful implementation in rodents to clinical applications in humans. However, information about how optogenetics influences the primate cortex remains limited. Here, we evaluate how optogenetic stimulation of the primate primary visual cortex (V1) affects local and large-scale network activation concerned with visual perception. To this end we injected an optogenetic construct (AAV9-hSyn-ChR2-eYFP) into the V1 cortex of four macaque monkeys (macaca mulatta) and measured the effects of optogenetic V1 stimulation using functional magnetic resonance imaging (fMRI), laminar electrophysiology, and behavioural assessment. In three macaques, blood-oxygen-dependent (BOLD) fMRI activity could be reliably elicited with optogenetic stimulation in V1 and several connected extrastriate brain areas, including V2/V3, motion-sensitive area MT and the frontal-eye-fields (FEF), in particular when pulsed stimulation at 40 Hz was applied. BOLD modulation was associated with consistent neural spiking activity measured in V1 of two macaques. More detailed analysis revealed strongest neuronal activation in layer 4B and infragranular layers, which tightly reflected the histological expression pattern of the optogenetic construct in V1. Driving this visual network proved sufficient to elicit a visual percept ( phosphene) in one macaque during a perceptual choice task. Taken together, our findings reveal the laminar and large-cortical activation pattern related to visual phosphene generation and emphasize the need for further improving optogenetic methods in NHPs as a step towards applications in humans.

neuroscience↗

bioRxiv2021

Dynamic reconfiguration of macaque brain networks during free-viewing of natural scenes

Natural vision involves the activation of a wide range of higher-level regions processing objects, motion, faces and actions. Here, we pursue a data-driven approach to explore how higher-level visual processes relate to the underlying structural and functional connectivity. Using a free-viewing paradigm in four awake rhesus macaque monkeys, we investigate how different visual scenes change functional connectivity. Additionally, we explore how such functional connectivity, as measured through fMRI, is related to the structural connectivity, as measured through diffusion weighted imaging. At first, we evaluate the consistency of the elicited free-viewing pattern using standard analytical techniques. We also evaluate the underlying structural connectivity via diffusion data by tracking white matter bundle projections from the visual cortex. We then reconstruct free-viewing and structural networks and quantify their properties. Centrality measures over the entire fMRI time-series revealed a consistent functional network engaged during free-viewing that included widespread hub regions across frontal (FEF, 46v), parietal (LIP, Tpt), and occipitotemporal cortex (MT, V4 and TE) among others. Interestingly, a small number of highly-weighted and long-length inter-hemispheric connections indicated the presence of long-range integrative properties during free-viewing. We hypothesized that during free-viewing, networks had the capacity to change their local and distal connections depending on the on-going changes in visual scenes. To capture these network dynamics, we depart from the static modular architecture of the structural networks and demonstrate that hubs in free-viewing networks reorganize according to the presence of objects, motion, and faces in the movie scenes indicating poly-functional properties. Lastly, we compare each NHP subject network and observe high consistency between individuals across the same network type with closer correspondence between structural networks (e.g., diffusion based and those partially assembled from tract-tracing). In summary, our network analyses revealed ongoing changes in large-scale functional organization present during free-viewing in the macaque monkey and highlight the advantages of multi-contrast imaging in awake monkeys for investigating dynamical processes in visual cognition. To further promote the use of naturalistic free-viewing paradigms and increase the development of macaque neuroimaging resources, we share our datasets in the PRIME-DE consortium.

neuroscience↗