Biology subjects

Ghose, G.

Publications and source records attributed to Ghose, G..

3 recordsLinked to original sources

bioRxiv2022

Task Demands Differentiate Regional Depth-Dependent Activity Profiles Within the Ventral Visual Pathway

FMRI has become a key tool for human neuroscience. At ultra-high field (=> 7 Tesla) it is possible to acquire images with submillimeter spatial precision, which allows examinations of mesoscale functional organization. Studying the brain at this scale does not come without its challenges, however. To tackle some of these challenges, we propose an approach that builds upon task modulations to identical visual stimuli and the simultaneous imaging of distal areas of varying complexity across the cortical hierarchy. Specifically, we record BOLD responses elicited by face stimuli during a stimulus relevant and a stimulus irrelevant task across cortical depths in V1, Occipital Face (OFA) and Fusiform Face area (FFA). We observed that task-related top-down modulations were larger in the inner compared to the outer layers of V1; and in the outer compared to the inner layers in the FFA. Our findings are consistent with animal reports of feedback exchange between deeper and superficial layers and with the notion of apical dendritic amplification as a key mechanism of conscious perception. Our approach showcases the potential of "laminar-fMRI" to explore large scale network activity and represents a promising step towards characterizing laminar functional profiles in humans for complex, cognitively meaningful, and socially relevant stimuli such as faces.

neuroscience↗

bioRxiv2021

Statistical Power or More Precise Insights into Neuro-Temporal Dynamics? Assessing the Benefits of Rapid Temporal Sampling in fMRI

Functional magnetic resonance imaging (fMRI), a non-invasive and widely used human neuroimaging method, is most known for its spatial precision. However, there is a growing interest in its temporal sensitivity. This is despite the temporal blurring of neuronal events by the blood oxygen level dependent (BOLD) signal, the peak of which lags neuronal firing by 4 to 6 seconds. Given this, the goal of this review is to answer a seemingly simple question - "What are the benefits of increased temporal sampling for fMRI?". To answer this, we have combined fMRI data collected at multiple temporal scales, from 323 to 1000 milliseconds, with a review of both historical and contemporary temporal literature. After a brief discussion of technological developments that have rekindled interest in temporal research, we next consider the potential statistical and methodological benefits. Most importantly, we explore how fast fMRI can uncover previously unobserved neuro-temporal dynamics - effects that are entirely missed when sampling at conventional 1 to 2 second rates. With the intrinsic link between space and time in fMRI, this temporal renaissance also delivers improvements in spatial precision. Far from producing only statistical gains, the array of benefits suggest that the continued temporal work is worth the effort.

neuroscience↗

bioRxiv2020

Domain-Specific Tasks Differentiate Cortical Areas with Similar Sensory Responses

The brain is organized into distinct, flexible networks. Within these networks, cognitive variables such as attention can modulate sensory representations in accordance with moment-to-moment behavioral requirements. These modulations can be studied by varying task demands; however, the tasks employed are often incongruent with the postulated functions of a sensory system, limiting the characterization of the system in relation to natural behaviors. Here we combine domain-specific task manipulations and ultra-high field fMRI to study the nature of top-down modulations. We exploited faces, a visual category underpinned by a complex cortical network, and instructed participants to perform either a stimulus-relevant/domain-specific or a stimulus-irrelevant task in the scanner. We found that 1. perceptual ambiguity (i.e. difficulty of achieving a stable percept) is encoded in top-down modulations from higher-level cortices; 2. the right inferior-temporal lobe is active under challenging conditions and uniquely encodes trial-by-trial variability in face perception.

neuroscience↗