Biology subjects

Shahnazian, D.

Publications and source records attributed to Shahnazian, D..

4 recordsLinked to original sources

bioRxiv2024

Exploring distinct and joint contributions of the Locus Coeruleus and the Substantia Nigra/Ventral Tegmental Area complex to reward and valence processing using high-resolution fMRI

Dopaminergic neurons in the substantia nigra and the ventral tegmental area (SN/VTA) are classically viewed as key mediators in reward processing, while noradrenergic cells in the locus coeruleus (LC) are thought to modulate (negative) saliency processing. However, this conventional distinction is being revised by more recent research in animals. To explore the respective contributions of both the LC and SN/VTA in reward and valence processing in humans, we assessed fMRI data during stimulus encoding and response phase of a rewarded emotion-discrimination task (n=38). Participants responded significantly faster to reward-predicting and negative valence stimuli compared to their non-salient counterparts. LC activity was overall higher during trials involving reward prospect, and in particular for reward trials featuring positive valence, demonstrating an additive effect of reward and positive valence in LC. Moreover, LC activity was differentially increased for negative compared to positive valence in the response phase, indexing its role in invigorating responses to negative events. The SN/VTA showed increased activity in the response phase of reward trials (neutral valence) and negative valence trials (no-reward), which aligns with coding relative saliency of these events in their respective contexts. LC modulations were accompanied by covariations in occipital cortex, suggesting noradrenergic contributions to visual prioritization of salient events. The findings underscore the sensitivity of both LC and SN/VTA to reward prospects and negative valence, challenging the dominant view of SN/VTAs involvement in merely positive events and emphasizing their essential role in action invigoration above and beyond mere stimulus encoding. The intricate roles of the DA and NA system in reward and emotional valence processing in humans warrant further exploration and validation, given the limitations inherent to neuroimaging of deep brain structures.

neuroscience↗

bioRxiv2020

Neural representations of task context and temporal order during action sequence execution

Since routine action sequences can share a great deal of similarity in terms of their stimulus response mappings, their correct execution relies crucially on the ability to preserve contextual and temporal information (Lashley, 1951). However, there are few empirical studies on the neural mechanism and the brain areas maintaining such information. To address this gap in the literature, we recently recorded the blood-oxygen level dependent (BOLD) response in a newly developed coffee-tea making task (Holroyd et al., 2018). The task involves the execution of 4 action sequences that each feature 6 decision states. Here we report a reanalysis of this dataset using a data-driven approach, namely multivariate pattern analysis (MVPA), that examines context-dependent neural activity across several predefined regions of interest. Results highlight involvement of the inferior-temporal gyrus and lateral prefrontal cortex in maintaining temporal and contextual information for the execution of hierarchically-organized action sequences. Furthermore, temporal information seems to be more strongly encoded in areas over the left hemisphere.

neuroscience↗

bioRxiv2019

Electrophysiological correlates of state transition prediction errors

Planning behavior depends crucially on the ability to distinguish between the likely and unlikely consequences of an action. Formal computational models of planning postulate the existence of a neural mechanism that tracks the transition model of the environment, i.e., a model that explicitly represents the probabilities of action consequences. However, empirical findings relating to such a mechanism are scarce. Here we report the results of two electroencephalographic experiments examining the neural correlates of transition model learning. The results implicate fronto-midline theta and delta oscillations in this process and suggest a role of the anterior midcingulate cortex in planning behavior.

neuroscience↗

bioRxiv2018

Subgoal- and Goal-Related Prediction Errors in Medial Prefrontal Cortex

A longstanding view of the organization of human and animal behavior holds that behavior is hierarchically organized, meaning that it can be understood as directed towards achieving superordinate goals through subordinate goals, or subgoals. For example, the superordinate goal of making coffee can be broken down as accomplishing a series of subgoals, namely boiling water, grinding coffee, pouring cream, etc. Learning and behavioral adaptation depend on prediction-error signals, which have been observed in ventral striatum (VS) and medial prefrontal cortex (mPFC). In past work, we have shown that prediction error signals (PEs) can be linked not only to superordinate goals, but also to subgoals. Here we present two functional magnetic resonance imagining experiments that replicate and extend these findings. In the first experiment, we replicated the finding that mPFC signals subgoal-related PEs, independently of goal PEs. Together with our past work, this experiment reveals that BOLD responses to PEs in mPFC are unsigned. In the second experiment, we showed that when a task involves both goal and subgoal PEs, mPFC shows only goal-related PEs, suggesting that context or attention can strongly impact hierarchical PE coding. Furthermore, we observed a dissociation between the coding of PEs in mPFC and VS. These experiments suggest that the mPFC selectively attends to information at different levels of hierarchy depending on the task context.

neuroscience↗