Biology subjects

Chopurian, V.

Publications and source records attributed to Chopurian, V..

4 recordsLinked to original sources

bioRxiv2025

Visuospatial working memory is cortically enabled through veridical, categorical and semantic representations

A single visual stimulus can elicit multiple concurrent representations throughout the cortex. We show that during a visual working memory task several cortical regions utilize categorical, semantic, and spatial representational formats to maintain visual stimuli in a robust fashion. We assessed the nature of orientation representations in an fMRI dataset of 40 participants performing an orientation memory task using multivariate encoding modelling. Our results show that orientation representations across the cortex form a gradient of abstraction, with more veridical representations in sensory areas and more abstract, categorical codes in anterior areas. We use cross-condition modelling to demonstrate shared neural codes between orientation and congruent verbal and location stimuli, used at different points during the trial. These findings provide evidence for a distributed account of working memory storage, where memory representations, distinct in nature and content, are present concurrently throughout the cortex.

neuroscience↗

bioRxiv2024

Distinct functional roles of distributed cortical representations for working memory storage

While distributed cortical areas represent working memory contents, their necessity for memory maintenance has been questioned. We examined the differential effects of maintaining multiple items on the neural information across cortical regions. In each trial of the fMRI experiment, participants (n=81) had to memorize two items, each either an orientation or a pure pitch, for 13.8s and continuously recalled the target after the delay. We kept the overall working memory load constant, but varied the sensory modality of each item to vary the effective visual load. We show that increasing visual load decreased behavioural recall performance for orientations and continuous orientation-specific decodable information in visual cortex but less so infrontoparietal areas. Simulations show that this drop in decodable information is best interpreted as a drop in mnemonic information represented by patterns of visual cortex activity. Our results provide evidence for shared labour of visual cortices, where maintaining two versus one orientation leads to a loss in representational fidelity, and anterior cortices, where multiple items could be represented in a more robust but less precise format.

neuroscience↗

bioRxiv2022

Dynamic regulation of neural variability during working memory reflects dopamine, functional integration, and decision-making

The regulation of moment-to-moment neural variability may permit effective responses to changing cognitive demands. However, the mechanisms that support variability regulation are unknown. In the context of working memory, we leverage the largest available PET and fMRI dataset to jointly consider three lenses through which neural variability regulation could be understood: dopamine capacity, network-level functional integration, and flexible decision processes. We show that with greater working memory load, upregulation of variability was associated with elevated dopamine capacity and heightened functional integration, effects dominantly expressed in the striato-thalamic system rather than cortex. Strikingly, behavioral modeling revealed that working memory load evoked substantial decision biases during evidence accumulation, and those who jointly expressed a more optimal decision bias and higher dopamine capacity were most likely to upregulate striato-thalamic variability under load. We argue that the ability to align striato-thalamic variability to level of demand may be a hallmark of a well-functioning brain.

neuroscience↗

bioRxiv2021

Effects of non-invasive brain stimulation on visual perspective taking: A meta-analytic study

Visual perspective taking (VPT) is a critical ability required by complex social interaction. Non-invasive brain stimulation (NIBS) has been increasingly used to examine the causal relationship between brain activity and VPT, yet with heterogeneous results. In the current study, we conducted two meta-analyses to examine the effects of NIBS of the right temporoparietal junction (rTPJ) or dorsomedial prefrontal cortex (dmPFC) on VPT, respectively. We performed a comprehensive literature search to identify qualified studies, and computed the standardized effect size (ES) for each combination of VPT level (Level-1: visibility judgment; Level-2: mental rotation) and perspective (self and other). Thirteen studies (rTPJ: 12 studies, 23 ESs; dmPFC: 4 studies, 14 ESs) were included in the meta-analyses. Random-effects models were used to generate the overall effects. Subgroup analyses for distinct VPT conditions were also performed. We found that rTPJ stimulation significantly improved participants visibility judgment from the allocentric perspective, whereas its effects on other VPT conditions are negligible. Stimulation of dmPFC appeared to influence Level-1 performance from the egocentric perspective, although it was only based on a small number of studies. Notably, contrary to some theoretical models, we did not find strong evidence that these regions are involved in Level-2 VPT with a higher requirement of mental rotation. These findings not only advanced our understanding of the causal roles of the rTPJ and dmPFC in VPT, but also revealed the efficacy of NIBS on VPT is relatively small. Researchers should also be cautious about the potential publication bias and selective reporting.

neuroscience↗