Biology subjects

Ramkiran, S.

Publications and source records attributed to Ramkiran, S..

3 recordsLinked to original sources

bioRxiv2023

Contribution of cortical layers to human dynamic functional connectivity

Transitory states of the brain, sometimes linked to particular mental disorders, can be identified by conducting a dynamic analysis of connectivity in functional magnetic resonance imaging (fMRI) data. Here, we investigated whether the connectivity between cortical laminae (in contrast to between cortical areas), can vary during the course of a resting-state scan and whether this could impact the identification of brain states in the healthy brain. We performed a sliding-window connectivity analysis of high-resolution fMRI data and found that the differential participation of the cortical layers in the overall cortical connectivity constitutes a more dynamic feature of the brain compared to region-to-region connectivity, with two main states (superficial vs. deep-laminae connectivity) fluctuating over time. Laminar connectivity restricted to the default mode network appeared relatively stable (superficial connectivity preferred), while the central executive and salience networks showed a fluctuating laminar preference. We anticipate that the dynamic analysis of connectivity focused on the different depths of the cerebral cortex could play an important role in characterizing healthy brain states as well as in identifying novel targets of psychiatric diseases.

neuroscience↗

bioRxiv2021

Modulation of the spontaneous brain activity and functional connectivity in the triple resting-state networks following the visual oddball paradigm

The default mode network (DMN), the salience network (SN), and the central executive network (CEN) could be considered as the core resting-state brain networks (RSN) due to their involvement in a wide range of cognitive tasks. Despite the large body of knowledge relating to their regional spontaneous activity (RSA) and functional connectivity (FC) of these networks, less is known about the influence of task-associated activity on these parameters and on the interaction between these three networks. We have investigated the effects of the visual-oddball paradigm on three fMRI measures (amplitude of low-frequency fluctuations for RSA, regional homogeneity for local FC, and degree centrality for global FC) in these three core RSN networks. A rest-task-rest paradigm was used and the RSNs were identified using independent component analysis (ICA) on the resting-state data. We found that the task-related brain activity induced different patterns of significant changes within the three RS networks. Most changes were strongly associated with the task performance. Furthermore, the task-activity significantly increased the inter-network correlations between the SN and CEN as well as between the DMN and CEN, but not between the DMN and SN. A significant dynamical change in RSA, alongside local and global FC within the three core resting-state networks following a simple cognitive activity may be an expression of the distinct involvement of these networks in the performance of the task and their various outcomes.

neuroscience↗

bioRxiv2020

Excitatory-Inhibitory Balance within EEG Microstates and Resting-state fMRI Networks: Assessed via Simultaneous PET-MR-EEG Imaging

The symbiosis of neuronal activities and glucose energy metabolism is reflected in the generation of functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) signals. However, their association with the balance between neuronal excitation and inhibition (E/I-B), which is closely related to the activities of glutamate and GABA ({gamma} -aminobutyric acid) and the receptor availability (RA) of GABAA and mGluR5, remains unexplored. This study investigates these associations during the resting state (RS) condition using simultaneously recorded PET/MR/EEG (trimodal) data. Glucose metabolism and neuroreceptor binding availability (non-displaceable binding potential (BPND)) of GABAA and mGluR5 were found to be significantly higher and closely linked within core resting-state networks (RSNs). The neuronal generators of EEG microstates and the fMRI measures were most tightly associated with the BPND of GABAA relative to mGluR5 BPND and the glucose metabolism, emphasising a predominance of inhibitory processes within in the core RSNs at rest.

neuroscience↗