Biology subjects

Menon, R. S.

Publications and source records attributed to Menon, R. S..

29 records · Page 2Linked to original sources

bioRxiv2021

Protocol-Dependence of Middle Cerebral Artery Dilation to Modest Hypercapnia

There is a need for improved understanding of how different cerebrovascular reactivity (CVR) protocols affect vascular cross-sectional area (CSA) when measures of vascular CSA are not feasible. In human participants, we delivered ~{+/-}4mmHg end-tidal partial pressure of CO2 (PETCO2) relative to baseline through controlled delivery, and measured changes in middle cerebral artery (MCA) cross-sectional area (CSA; magnetic resonance imaging (7 Tesla MRI)), blood velocity (transcranial Doppler and Phase contrast MRI), and calculated CVR based on steady-state versus a ramp protocol during two protocols: a 3-minute steady-state (+4mmHg PETCO2) and a ramp (delta of -3 to +4mmHg of PETCO2). We observed that 1) the MCA did not dilate during the ramp protocol, but did dilate during steady-state hypercapnia, and 2) MCA blood velocity CVR was similar between ramp and steady-state hypercapnia protocols, although calculated MCA blood flow CVR was greater during steady-state hypercapnia than during ramp, the discrepancy due to MCA CSA changes during steady-state hypercapnia. Due to the ability to achieve similar levels of MCA blood velocity CVR as steady-state hypercapnia, the lack of change in MCA cross-sectional area, and the minimal expected change in blood pressure, we propose that a ramp model, across a delta of ~-3 to +4mmHg PETCO2, may provide one alternative approach to collecting CVR measures in young adults with TCD when CSA measures are not feasible.

physiology↗

bioRxiv2021

Interspecies activation correlations reveal functional correspondences between marmoset and human brain areas

The common marmoset has enormous promise as a nonhuman primate model of human brain functions. While resting-state functional magnetic resonance imaging (fMRI) has provided evidence for a similar organization of marmoset and human cortices, the technique cannot be used to map the functional correspondences of brain regions between species. This limitation can be overcome by movie-driven fMRI (md-fMRI), which has become a popular tool for non-invasively mapping the neural patterns generated by rich and naturalistic stimulation. Here, we used md-fMRI in marmosets and humans to identify whole-brain functional correspondences between the two primate species. In particular, we describe functional correlates for the well-known human face, body, and scene patches in marmosets. We find that these networks have a similar organization in both species, suggesting a largely conserved organization of higher-order visual areas between New World marmoset monkeys and humans. However, while face patches in humans and marmosets were activated by marmoset faces, only human face patches responded to the faces of other animals. Together, the results demonstrate that md-fMRI is a powerful tool for interspecies functional mapping and characterization of higher-order visual functions.

neuroscience↗

bioRxiv2021

Simultaneous functional MRI of socially interacting marmosets

Social cognition is a dynamic process that requires the perception and integration of a complex set of idiosyncratic features between interacting conspecifics. Here we present a method for simultaneously measuring the whole-brain activation of two socially interacting marmoset monkeys using functional magnetic resonance imaging. MRI hardware (a radiofrequency coil and peripheral devices) and image-processing pipelines were developed to assess brain responses to socialization, both on an intra-brain and inter-brain level. Notably, brain-activation maps acquired during constant interaction demonstrated neuronal synchrony between marmosets in regions of the brain responsible for processing social interaction. This method enables a wide range of possibilities for studying social function and dysfunction in a non-human primate model, including using transgenic models of neuropsychiatric disorders.

neuroscience↗

bioRxiv2020

Cortico-subcortical functional connectivity profiles of resting-state networks in marmosets and humans

Understanding the similarity of cortico-subcortical networks topologies between humans and nonhuman primate species is critical to study the origin of network alternations underlying human neurological and neuropsychiatric diseases. The New World common marmoset (Callithrix jacchus) has become popular as a non-human primate model for human brain function. Most marmoset connectomic research, however, has exclusively focused on cortical areas, with connectivity to subcortical networks less extensively explored. In this study, we aimed to first isolate patterns of subcortical connectivity with cortical resting-state networks (RSNs) in awake marmosets using resting-state functional magnetic resonance imaging (RS-fMRI), then to compare these networks to those in humans using connectivity fingerprinting. While we could match several marmoset and human RSNs based on their functional fingerprints, we also found a few striking differences, for example strong functional connectivity of the default mode network with the superior colliculus in marmosets that was much weaker in humans. Together, these findings demonstrate that many of the core cortico-subcortical networks in humans are also present in marmosets, but that small, potentially functionally relevant differences exist.

neuroscience↗

bioRxiv2020

Structural alterations in the macaque frontoparietal white matter network after recovery from prefrontal cortex lesions

Unilateral damage to the frontoparietal network typically impairs saccade target selection within the contralesional visual hemifield. Severity of deficits and the degree of recovery have been associated with widespread network dysfunction, yet it is not clear how these behavioural and functional changes relate with the underlying structural white matter pathways. Here, we investigated whether recovery after unilateral prefrontal cortex (PFC) lesions was associated with structural white matter remodeling in the distributed frontoparietal network. Diffusion-weighted MRI was acquired in four macaque monkeys before the lesions and at 2-4 months post-lesion, after recovery of deficits in saccade selection of contralesional targets. Probabilistic tractography was used to reconstruct inter- and intra-hemispheric frontoparietal fiber tracts: bilateral superior longitudinal fasciculus (SLF) and transcallosal fibers connecting bilateral PFC or bilateral posterior parietal cortex (PPC). After behavioural recovery, tract-specific fractional anisotropy in contralesional SLF and transcallosal PPC increased after small lesions and decreased after larger lesions compared to pre-lesion. These findings indicate that remote fiber tracts may provide optimal compensation after small PFC lesions. However, larger lesions may have induced widespread structural damage and hindered compensatory remodeling in the structural frontoparietal network.

neuroscience↗

bioRxiv2020

Face selective patches in marmoset frontal cortex

Primates have evolved the ability transmit important social information through facial expression. In humans and macaque monkeys, socially relevant face processing is accomplished via a distributed cortical and subcortical functional network that includes specialized patches in anterior cingulate cortex and lateral prefrontal cortex, regions usually associated with high-level cognition. It is unclear whether a similar network exists in New World primates, who diverged ~35 million years from Old World primates and have a less elaborated frontal cortex. The common marmoset (Callithrix jacchus) is a small New World primate that is ideally placed to address this question given the complex social repertoire inherent to this species (e.g., observational social learning; imitation; cooperative antiphonal calling). Here, we investigated the existence of a putative high-level face processing network in marmosets by employing ultra-high field (9.4 Tesla) task-based functional MRI (fMRI). We demonstrated that, like Old World primates, marmosets show differential activation in anterior cingulate cortex and lateral prefrontal cortex while they view socially relevant videos of marmoset faces. We corroborate the locations of these frontal regions by demonstrating both functional (via resting-state fMRI) and structural (via cellular-level tracing) connectivity between these regions and temporal lobe face patches. Given the evolutionary separation between macaques and marmosets, our results suggest this frontal network specialized for social face processing predates the separation between Platyrrhini and Catarrhine. These results give further credence to the marmoset as a viable preclinical modelling species for studying human social disorders.

neuroscience↗

bioRxiv2020

Effects of MP2RAGE B1+ sensitivity on inter-site T1 reproducibility and morphometry at 7T

Most neuroanatomical studies are based on MR images, whose intensity profiles are not solely determined by the tissues longitudinal relaxation times (T1) but also affected by varying non-T1 contributions, hampering data reproducibility. In contrast, quantitative imaging using the MP2RAGE sequence, for example, allows direct characterization of the brain based on the tissue property of interest. Combined with 7 Tesla (7T) MRI, this offers unique opportunities to obtain robust high-resolution brain data characterized by a high reproducibility, sensitivity and specificity. However, specific MP2RAGE parameters choices - e.g., to emphasize intracortical myelin-dependent contrast variations - can substantially impact image quality and cortical analyses through remnants of B1+-related intensity variations, as illustrated in our previous work. To follow up on this: we (1) validate this protocol effect using a dataset acquired with a particularly B1+ insensitive set of MP2RAGE parameters combined with parallel transmission excitation; and (2) extend our analyses to evaluate the effects on hippocampal and subcortical morphometry. The latter remained unexplored initially but will provide important insights related to generalizability and reproducibility of neurodegenerative research using 7T MRI. We confirm that B1+ inhomogeneities have a considerably variable effect on cortical T1 and thickness estimates, as well as on hippocampal and subcortical morphometry depending on MP2RAGE setup. While T1 differed substantially across datasets initially, we show inter-site T1 comparability improves after correcting for the spatially varying B1+ field using a separately acquired Sa2RAGE B1+ map. Finally, as for cortical thickness, removal of B1+ residuals affects hippocampal and subcortical volumetry and boundary definitions, particularly near structures characterized by strong intensity changes (e.g. cerebral spinal fluid and arteries). Taken together, we show that the choice of MP2RAGE parameters can impact T1 comparability across sites and present evidence that hippocampal and subcortical segmentation results are modulated by B1+ inhomogeneities. This calls for careful (1) consideration of sequence parameters when setting acquisition protocols; as well as (2) interpretation of results focused on neuroanatomical changes due to disease. HighlightsO_LIPreviously observed effects of B1+ inhomogeneities on cortical T1 and thickness depend strongly on MP2RAGE parameters C_LIO_LIInter-site comparability of cortical T1 and thickness greatly improves after removal of B1+ residuals C_LIO_LIPost-hoc MP2RAGE B1+ correction affects hippocampal (and subcortical) size and shape analyses C_LIO_LINeuroradiological research would benefit from careful examination of imaging protocols and their impact on results, especially when B1+ maps are not acquired C_LI

neuroscience↗

bioRxiv2019

Dynamic reconfiguration, fragmentation and integration of whole-brain modular structure across depths of unconsciousness

General anesthetics are routinely used to induce unconsciousness, and much is known about their effects on receptor function and single neuron activity. Much less is known about how these local effects are manifest at the whole-brain level, nor how they influence network dynamics, especially past the point of induced unconsciousness. Using resting-state functional magnetic resonance imaging (fMRI) with nonhuman primates, we investigated the dose-dependent effects of anesthesia on whole-brain temporal modular structure, following loss of consciousness. We found that higher isoflurane dose was associated with an increase in both the number and isolation of whole-brain modules, as well as an increase in the uncoordinated movement of brain regions between those modules. Conversely, we found that higher dose was associated with a decrease in the cohesive movement of brain regions between modules, as well as a decrease in the proportion of modules in which brain regions participated. Moreover, higher dose was associated with a decrease in the overall integrity of networks derived from the temporal modules, with the exception of a single, sensory-motor network. Together, these findings suggest that anaesthesia-induced unconsciousness results from the hierarchical fragmentation of dynamic whole-brain network structure, leading to the discoordination of temporal interactions between cortical modules.

neuroscience↗

bioRxiv2019

Visual looming and receding networks in awake marmosets investigated with fMRI

An object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. This information (motion, direction, identity, time-to-collision, size, velocity) is analyzed by the brain in order to execute the appropriate behavioral responses depending on the context: fleeing, freezing, grasping, eating, exploring. In the current study, we performed ultra-high-field functional MRI (fMRI) in awake marmosets to explore the patterns of brain activation elicited by visual stimuli looming toward or receding away from the monkey. We found that looming and receding visual stimuli both activate a large cortical network in frontal, parietal, temporal and occipital cortex in areas involved in the analysis of motion, shape, identity and features of the objects. Looming stimuli strongly activated a network composed of the pulvinar, superior colliculus, prefrontal cortex and temporal cortical areas. This may underlie the existence of an alert network that processes the visual stimuli looming toward their peripersonal space by extracting the crucial information brought by the stimulus and evaluating its potential consequences to the observer. We hypothesize that this network is involved in the planning of protective behaviors (e.g. fleeing or freezing) and in emotional reaction (e.g. anxiety, fear). These findings support the view that this network is preserved through evolution and that the marmoset is a viable model to study visual and multisensory processes by using fMRI to guide further invasive recordings and/or pharmacological manipulations.\n\nSignificant statementAn object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless to them. Here, we identified the functional network in non-human primates that was activated by visual stimuli looming toward or away from the animals using ultra-high-field functional magnetic resonance imaging. Our findings show that large cortical activations are elicited by both looming and receding visual conditions. However, some activations were specific to the looming condition, suggesting that the integration of cues in the looming direction rely on strong connections between cortical and subcortical areas, which allows primates to react properly for protecting themselves against a potential threat.

neuroscience↗

bioRxiv2018

Exploring the limits of network topology estimation using diffusion-based tractography and tracer studies in the macaque cortex

Reconstructing the anatomical pathways of the brain to study the human connectome has become an important endeavour for understanding brain function and dynamics. Reconstruction of the cortico-cortical connectivity matrix in vivo often relies on noninvasive diffusion-weighted imaging (DWI) techniques but the extent to which they can accurately represent the topological characteristics of structural connectomes remains unknown. We explored this question by constructing connectomes using DWI data collected from macaque monkeys in vivo and with data from published invasive tracer studies. We found the strength of fiber tracts was well estimated from DWI and topological properties like degree and modularity were captured by tractography-based connectomes. Rich-club/core-periphery type architecture could also be detected but the classification of hubs using betweenness centrality, participation coefficient and core-periphery identification techniques was inaccurate. Our findings indicate that certain aspects of cortical topology can be faithfully represented in noninvasively-obtained connectomes while other network analytic measures warrant cautionary interpretations.

neuroscience↗

bioRxiv2017

An open resource for nonhuman primate imaging

Non-human primate neuroimaging is a rapidly growing area of research that promises to transform and scale translational and cross-species comparative neuroscience.\n\nUnfortunately, the technological and methodological advances of the past two decades have outpaced the accrual of data, which is particularly challenging given the relatively few centers that have the necessary facilities and capabilities. The PRIMate Data Exchange (PRIME-DE) addresses this challenge by aggregating independently acquired non-human primate magnetic resonance imaging (MRI) datasets and openly sharing them via the International Neuroimaging Data-sharing Initiative (INDI). Here, we present the rationale, design and procedures for the PRIME-DE consortium, as well as the initial release, consisting of 13 independent data collections aggregated across 11 sites (total = 98 macaque monkeys). We also outline the unique pitfalls and challenges that should be considered in the analysis of the non-human primate MRI datasets, including providing automated quality assessment of the contributed datasets.

neuroscience↗