Biology subjects

Corbetta, M.

Publications and source records attributed to Corbetta, M..

8 recordsLinked to original sources

bioRxiv2018

Architecture of functional lateralisation in the human brain

Functional lateralisation is a fundamental principle of the human brain. However, a comprehensive taxonomy of functional lateralisation and its organisation in the brain is missing. We report the first complete map of functional hemispheric asymmetries in the human brain, reveal its low dimensional structure, and its relationship with structural inter-hemispheric connectivity. Our results suggest that the lateralisation of brain functions is distributed along four functional axes: symbolic communication, perception/action, emotion, and decision-making, and that cortical regions showing asymmetries in task-evoked activity have reduced connections with the opposite hemisphere.

neuroscience↗

bioRxiv2018

Comparison of stimulus-evoked BOLD responses in human and monkey visual cortex

We characterized the blood oxygenation level dependent (BOLD) signal in humans and macaque monkeys by comparing the response in visual cortex to a single checkerboard or two checkerboards, spaced 1.5, 3.0, or 4.5 s apart. We found that the magnitude and shape of the BOLD response to a single checkerboard was similar in the two species. In addition, we found that the BOLD responses summed similarly, and that at an inter-stimulus interval (ISI) of 4.5 sec BOLD summation was nearly linear in both species. When comparing the ratio of the amplitude of the response to the second checkerboard at the 4.5 sec ISI with that of the single checkerboard between subjects in both species, the results from both monkey subjects fell within one standard deviation of the mean human results (human mean (n=12): .95 +/- .31 second/single response amplitude; monkey 1: 1.16; monkey 2: .86). At the shorter ISIs, both species demonstrated increased suppression of the BOLD response to the second checkerboard. These findings indicate that the magnitude of the BOLD response to events separated by 4.5 seconds can be accurately measured in and compared between human and monkey visual cortex.

neuroscience↗

bioRxiv2018

Topographic Organization of Extraoccipital Visual Processing Areas in the Macaque

The macaque visual system has long been used as a model for investigating the processing of incoming visual stimuli results from the coordinated work of a distributed network of areas interacting at many different levels (Felleman and Van Essen, 1991). While much is known about the organization and layout of the occipital visual areas, there are still substantial gaps in our understanding of layout and organization of the higher-level areas. The goal of this study is to describe the whole brain functional anatomy using BOLD-fMRI in macaques performing a series of demanding visuospatial attention tasks. We wish to study the spatial specificity of visual responses in terms of contralateral preference, i.e. stronger responses to contralateral visual stimuli, as well as retinotopic organization both in terms of polar angle and eccentricity. We found that most visuospatial processing areas only respond to contralaterally presented stimuli; ipsilaterally presented stimuli evoked little or no activity in these areas. Additionally, we found that LIP, MT, and possibly PITd contained polar-angle maps of the contralateral hemifield. These same areas, plus FEF and area 46, appear to have separate representations of the fovea and periphery. When compared to previous human fMRI studies, these results indicate that there may be significant differences between macaque visual processing areas and their putative human homologues.

neuroscience↗

bioRxiv2018

Attentional Modulation of Macaque Visual Processing Areas

Introduction Introduction Materials and Methods Results Discussion References The visual expectation that an object will appear at a certain location or time may increase the accuracy and speed of its detection (Eriksen and Hoffman, 1974; Posner, 1980; Carrasco et al., 2000; Dosher and Z-L., 2000). The ability to use prior information to enhance the processing of visual stimuli at a specific location is critical for quickly sorting through the myriad of incoming stimuli and making decisions regarding future actions. This selection process, known as visual attention, appears to be fundamental to our ability to navigate and interact with the environment, and accordingly has been the focus of innumerable psychological and neurobiological studies (Pa ...

neuroscience↗

bioRxiv2018

Archetypes in human behavior and their brain correlates: An evolutionary trade-off approach

Organisms perform multiple tasks and in doing so face critical trade-offs. According to Pareto optimality theory, such trade-offs lead to the evolution of phenotypes that are distributed in a portion of the trait-space resembling a polytope, whose vertices represent the specialists at one of the traits (archetypes).\n\nWe applied this theory to the variability of cognitive and behavioral scores measured in 1206 individuals from the Human Connectome Project. Among all possible 300 combinations of pairs of traits, we found the best fit to Pareto optimality when individuals were plotted in the trait-space of time preferences for reward, evaluated with the Delay Discounting task. This task requires choosing either immediate smaller rewards or delayed larger rewards. Time preference for reward identified three archetypes, which accounted for variability on many cognitive, personality, and socio-economic status scores, differences in brain structure, as well as in functional connectivity between prefrontal cortex, basal ganglia, and amygdala, regions associated with reward and their regulation. There was only a weak association with genetics. In summary, time preference for reward reflects a core variable that biases human phenotypes via natural and cultural selection.

neuroscience↗

bioRxiv2018

Distinct Functional Connectivity Mode during Viewing Natural Scenes Revealed by Principal Component Analysis

A fundamental question in systems neuroscience is how spontaneous activity at rest is reorganized during task performance. Recent studies suggest a strong relationship between resting and task FC. Furthermore, the relationship between resting and task FC has been shown to reflect individual differences. Particularly, various studies have demonstrated that the FC has higher reliability and provides enhanced detection of individual differences while viewing natural scenes. Although the large-scale organization of FC during rest and movie-viewing conditions have been well studied in relation to individual variations, the re-organization of FC during viewing natural scenes have not been studied in depth. In this study, we used principal component analysis on FC during rest and movie-viewing condition to characterize the dimensionality of FC patterns across conditions and subjects. We found that the variations in FC patterns related to viewing natural scenes can be explained by a single component, which enables identification of the task over subjects with 100% accuracy. We showed that the FC mode associated to viewing natural scenes better reflects individual variations. Furthermore, we investigated the signatures of movie-viewing-specific functional modes in dynamic FC based on phase-locking values between brain regions. We found that the movie-specific functional mode is persistent across time; suggesting the emergence of a stable processing mode. To explain the reorganization of whole-brain FC through the changes in local dynamics, we appeal to a large-scale computational model. This modelling suggested that the reorganization of whole-brain FC is associated to the interaction between frontal-parietal and frontal-temporal activation patterns.

neuroscience↗

bioRxiv2017

Measuring functional connectivity in stroke: approaches and considerations

Recent research has demonstrated the importance of global changes to the functional organization of brain network following stroke. Resting functional MRI (R-fMRI) is a non-invasive tool that enables the measurement of functional connectivity (FC) across the entire brain while placing minimal demands on the subject. For these reasons, it is a uniquely appealing tool for studying the distant effects of stroke. However, R-fMRI studies rely on a number of premises that cannot be assumed without careful validation in the context of stroke. Here, we describe strategies to identify and mitigate confounds specific to R-fMRI research in cerebrovascular disease. Five main topics are discussed: 1) achieving adequate co-registration of lesioned brains, 2) identifying and removing hemodynamic lags in resting BOLD, 3) identifying other vascular disruptions that affect the resting BOLD signal, 4) selecting an appropriate control cohort, and 5) acquiring sufficient fMRI data to reliably identify FC changes. For each topic, we provide evidence-based guidelines for steps to improve the interpretability and reproducibility of FC-stroke research. We include a table of confounds and approaches to identify and mitigate each. Our recommendations extend to any research using R-fMRI to study diseases that might alter cerebrovascular flow and dynamics or brain anatomy.

neuroscience↗

bioRxiv2017

Effective connectivity inferred from fMRI transition dynamics during movie viewing points to a balanced reconfiguration of cortical interactions

Our behavior entails a flexible and context-sensitive interplay between brain areas to integrate information according to goal-directed requirements. How-ever, the neural mechanisms governing the entrainment of functionally specialized brain areas remain poorly understood. In particular, the question arises whether observed changes in the regional activity for different cognitive conditions are explained by modifications of the inputs to the brain or its connectivity? We observe that transitions of fMRI activity between areas convey information about the tasks performed by 19 subjects, watching a movie versus a black screen (rest). We use a model-based framework that explains this spatiotemporal functional connectivity pattern by the local variability for 66 cortical regions and the network effective connectivity between them. We find that, among the estimated model parameters, movie viewing affects to a larger extent the local activity, which we interpret as extrinsic changes related to the increased stimulus load. However, detailed changes in the effective connectivity preserve a balance in the propagating activity and select specific pathways such that high-level brain regions integrate visual and auditory information, in particular boosting the communication between the two brain hemispheres. These findings speak to a dynamic coordination underlying the functional integration in the brain.

neuroscience↗