Biology subjects

Sanchez-Fibla, M.

Publications and source records attributed to Sanchez-Fibla, M..

3 recordsLinked to original sources

bioRxiv2021

Meditation-induced effects on whole-brain structural and effective connectivity

In the past decades, there has been a growing scientific interest in characterizing neural correlates of meditation training. Nonetheless, the mechanisms underlying meditation remain elusive. In the present work, we investigated meditation-related changes in structural and functional connectivities (SC and FC, respectively). For this purpose, we scanned experienced meditators and control (naive) subjects using magnetic resonance imaging (MRI) to acquire structural and functional data during two conditions, resting-state and meditation (focused attention on breathing). In this way, we aimed to characterize and distinguish both short-term and long-term modifications in the brains structure and function. First, we performed a network-based analysis of anatomical connectivity. Then, to analyze the fMRI data, we calculated whole-brain effective connectivity (EC) estimates, relying on a dynamical network model to replicate BOLD signals spatio-temporal structure, akin to FC with lagged correlations. We compared the estimated EC, FC, and SC links as features to train classifiers to predict behavioral conditions and group identity. The whole-brain SC analysis revealed strengthened anatomical connectivity across large-scale networks for meditators compared to controls. We found that differences in SC were reflected in the functional domain as well. We demonstrated through a machine-learning approach that EC features were more informative than FC and SC solely. Using EC features we reached high performance for the condition-based classification within each group and moderately high accuracies when comparing the two groups in each condition. Moreover, we showed that the most informative EC links that discriminated between meditators and controls involved the same large-scale networks previously found to have increased anatomical connectivity. Overall, the results of our whole-brain model-based approach revealed a mechanism underlying meditation by providing causal relationships at the structure-function level.

neuroscience↗

bioRxiv2020

Habituation and Goal-directed arbitration mechanisms and failures under partial observability

AO_SCPLOWBSTRACTC_SCPLOWWe often need to make decisions under incomplete information (partial observability) and the brain manages to add the right minimal context to the decision-making. Partial observability may also be handled by other mechanisms than adding contextual experience / memory. We propose that parallel and sequential arbitration of Habituation (Model-Free, MF) and Goal-Directed (Model-Based, MB) behavior may be at play to deal with partial observability "on-the-fly", and that MB may be of different types (going beyond the MF/MB dichotomy [4]). To illustrate this, we identify, describe and model with Reinforcement Learning (RL) a behavioral anomaly (an habituation failure) occurring during the so-called Hotel Elevators Rows (HER, for short) task: a prototypical partial observation situation that can be reduced to the well studied Two and One Sequence Choice Tasks. The following hypothesis are supported by RL simulation results: (1) a parallel (semi)model-based successor representation mechanism is operative while learning to habituate which detects model-based mismatches and serves as an habituation surveillance, (2) a retrospective inference is triggered to identify the source of the habituation failure (3) a model-free mechanism can trigger model-based mechanisms in states in which habituation failed. The "failures" in the title refer to: the habituation failures that need to be monitored and surveilled (1) and to the failures that we identified in prototypical state of the art Model-Based algorithms (like DynaQ) when facing partial observability. As other research on MF/MB arbitration shows, the identification of these new mechanisms could shine light into new treatments for addiction, compulsive behavior (like compulsive checking) and understand better accidents caused by habituation behaviors.

neuroscience↗

bioRxiv2017

The Perceptual Shaping of Anticipatory Actions

Humans display anticipatory motor responses to minimize the adverse effects of predictable perturbations. A widely accepted explanation for this behavior relies on the notion of an inverse model that, learning from motor errors, anticipates corrective responses. Here, we propose and validate the alternative hypothesis that anticipatory control can be realized through a cascade of purely sensory predictions that drive the motor system, reflecting the causal sequence of the perceptual events preceding the error. We compare both hypotheses in a simulated anticipatory postural adjustment task. We observe that adaptation in the sensory domain, but not in the motor one, supports the robust and generalizable anticipatory control characteristic of biological systems. Our proposal unites the neurobiology of the cerebellum with the theory of active inference and provides a concrete implementation of its core tenets with great relevance both to our understanding of biological control systems and, possibly, to their emulation in complex artefacts.

neuroscience↗