Biology subjects

Khosrowabadi, R.

Publications and source records attributed to Khosrowabadi, R..

9 recordsLinked to original sources

bioRxiv2025

Opposite Priming Effects on Identity vs. Category Recognition Require Conscious Awareness

How conscious and unconscious priming differentially modulate object recognition at different levels of abstraction (identity vs. category) remains incompletely understood, despite extensive research. We used a binocular rivalry paradigm with Continuous Flash Suppression (CFS) to manipulate conscious awareness with image or word primes while participants performed a name-picture verification task probing identity and category recognition for faces and animal bodies. Behavioral results revealed a striking dissociation: consciously perceived primes facilitated identity recognition but impaired category recognition. This effect was most pronounced with image primes, face targets, and right visual field presentations. Under unconscious priming, no such effects were observed. To elucidate the underlying mechanism, we applied a Drift Diffusion Model, which revealed that conscious priming selectively enhanced the efficiency of evidence accumulation and introduced a pre-decisional bias for identity decisions, with no reliable change for category decisions. Our findings demonstrate a double dissociation where conscious awareness is required for priming to exert robust and opposite effects on identity and category recognition. This finding challenges the view of priming as a uniformly facilitatory process, providing a new mechanistic framework for understanding how consciousness and abstraction level interact to shape visual perception. HighlightsO_LIConscious awareness is required for priming to exert robust effects on recognition C_LIO_LIThe priming aftereffects can be facilitatory or impairing depending on the level of recognition C_LIO_LIConscious priming facilitated identity recognition but impaired category recognition. C_LIO_LIDissociation of identity and category by conscious priming were strongest for image (vs. word) primes, face (vs. animal) targets, and right (vs. left) visual field presentations. C_LIO_LIDrift diffusion modeling revealed increased drift rate and pre-decisional bias, for identity but not for category decisions in conscious priming. C_LI

neuroscience↗

bioRxiv2024

A Causal Role of the Right Dorsolateral Prefrontal Cortex in Random Exploration

Our brain faces the dilemma of exploiting familiar options to gain immediate rewards or exploring new options to increase probable future rewards, in many real-life decisions, and solves it by direct and random exploration. Previous studies show that these two explorative strategies have dissociable neural correlates in the brain. Using the continuous theta burst stimulation (cTBS) and horizon task, we investigate the causal role of the right dorsolateral prefrontal cortex (rDLPFC) in direct and random exploration. Twenty-five healthy right-handed adult participants underwent cTBS, and vertex stimulation sessions, and then completed the horizon tasks. Both model-free and model-based analysis showed that cTBS over rDLPFC selectively reduced random exploration, but not direct exploration. This suggests a causal role for rDLPFC especially in random exploration, and further supports dissociable neural implementations for direct and random exploration. (C) 2024 The Author(s)

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bioRxiv2022

Dysfunctional feedback processing in methamphetamine abuser; evidence from neurophysiological and computational analysis

Methamphetamine use disorder associated with a dysfunctional neural feedback (reward-punishment) processing system and is considered a public health risk. Although several behavioral, computational, and electrocortical studies have explored feedback processing in other groups of individuals, the precise mechanisms of feedback processing dysfunction in methamphetamine use dependent (MUD) individuals remain unclear. Furthermore, our recent knowledge about the underlying feedback-related connectivity patterns and intertwining latent components of behavior with electrocortical signals in MUDs remained quite poor. The present study intended to fill these gaps by exploring the behavioral and electrocortical responses of abstained MUDs during a feedback-based learning paradigm. As mathematical models revealed, MUDs have less sensitivity to distinguishing optimal options (less sensitivity to options value) and learned less from negative feedback, compared with healthy controls. The MUDs also presented smaller medial-frontal theta (5-8 Hz) oscillations in response to negative feedback (300-550 ms post feedback) while other measures responsible for learning including, feedback-related negativity (FRN), parietal-P300, and a flux originated from medial frontal to lateral prefrontal remained intact for them. Further, in contrast to healthy controls, the observed association between feedback sensitivity and medial-frontal theta activity is eliminated in MUDs. We suggested that these results in MUDs may be due to the adverse effect of methamphetamine on the cortico-striatal dopamine circuit, reflected in anterior cingulate cortex (ACC) activity as the best candidate region responsible for efficient behavior adjustment. This study unveils the underlying neural mechanism of feedback processing in individuals with methamphetamine use history and could offer individual therapeutic approaches.

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bioRxiv2022

Pattern of frustration formation in the functional brain network

The brain is a frustrated system that contains conflictual link arrangements named frustration. The frustration as a source of disorder prevents the system from settling into low energy states and provides flexibility for brain network organization. In this research, we tried to identify the pattern of frustration formation in the brain at the levels of region, connection, canonical network, and hemisphere. We found that frustration formation has not a uniform pattern. Some subcortical elements have an active role in frustration formation, despite many low contributed cortical elements. Frustrating connections are mostly between-network types and triadic frustrations are mainly formed between three regions from three distinct canonical networks. Although there were no significant differences between brain hemispheres. We also did not find any robust differences between the frustration formation patterns of various lifespan stages. Our results may be interesting for those who study the organization of brain links and promising for those who want to manipulate brain networks.

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bioRxiv2021

Electrophysiological markers of fairness and selfishness revealed by a combination of Dictator and Ultimatum Games

AO_SCPLOWBSTRACTC_SCPLOWEvent Related Potentials (ERPs) were recorded from 39 participants who played the role of Allocators in a Dictator Game (DG) and Responders in an Ultimatum Game (UG). Most participants expressed very low levels of altruistic decision making, and two homogeneous groups could be identified, one formed by fair (N = 10) individuals and another by selfish (N = 8) individuals. At fronto-central cortical sites, the ERP early negativity (N1) was reduced in selfish participants with a latency about 10 ms earlier than in fair participants. In fair DG players, the features of the subsequent positive wave P2 suggested that more cognitive resources were required when they allocated the least gains to the other party. P2 latency and amplitude in the selfish group supported the hypothesis that these participants tended to maximize their profit, as expected by a rational Homo economicus. During UG, we observed that a medial frontal negativity (MFN) occurred earlier and with greater amplitude when selfish participants rejected less favorable endowment shares. In this case, all players received zero payoffs, which showed that MFN in selfish participants was associated with a spiteful punishment. At posterior-parietal sites we found that the greater the selfishness, the greater the amplitude of the late positive component (LPC). Our results bring new evidence to the existence of specific somatic markers associated with the activation of distinct cerebral circuits by the evaluation of fair and unfair proposals in participants characterized by different expressions of perceived fairness, thus suggesting that particular brain dynamics could be associated with moral decisions.

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bioRxiv2021

Fractal dimension of EEG signal senses complexity of fractal animations

We are surrounded with many fractal and self-similar patterns which has been area of many researches in the recent years. We can perceive self-similarities in various spatial and temporal scales; however, the underlying neural mechanism needs to be well understood. In this study, we hypothesized that complexity of visual stimuli directly influence complexity of information processing in the brain. Therefore, changes in fractal pattern of EEG signal must follow change in fractal dimension of animation. To investigate this hypothesis, we recorded EEG signal of fifteen healthy participants while they were exposed to several 2D fractal animations. Fractal dimension of each frame of the animation was estimated by box counting method. Subsequently, fractal dimensions of 32 EEG channels were estimated in a frequency specific manner. Then, association between pattern of fractal dimensions of the animations and pattern of fractal dimensions of EEG signals were calculated using the Pearsons correlation algorithm. The results indicated that fractal animation complexity is mainly sensed by changes in fractal dimension of EEG signals at the centro-parietal and parietal regions. It may indicate that when the complexity of visual stimuli increases the mechanism of information processing in the brain also enhances its complexity to better attend and comprehend the stimuli.

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bioRxiv2021

Topological impact of negative links on the stability of resting-state brain network

Stability is a physical attribute that stands opposite the change. However, it is still unclear how the arrangement of links called topology affects network stability. In this study, we tackled this issue in the resting-state brain network using structural balance. Structural balance theory employs the quality of triadic associations between signed links to determine the network stability. In this study, we showed that negative links of the resting-state network make hubs to reduce balance-energy and push the network into a more stable state compared to null-networks with trivial topologies. In this regard, we created a global measure entitled tendency to make hub to assess the hubness of the network. Besides, we revealed nodal degrees of negative links have an exponential distribution that confirms the existence of negative hubs. Our findings indicate that the arrangement of negative links plays an important role in the balance (stability) of the resting-state brain network.

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bioRxiv2019

Decoupling of inter-regional functional connectivity and regional neural activity in Alzheimer Disease

Alzheimers disease (AD) and mild cognitive impairment (MCI) are characterized by aberrant regional neural activity and disrupted inter-regional functional connectivity (FC). It is, however, poorly understood how changes in regional neural activity and inter-regional FC interact in AD and MCI. Here, we investigated the link between regional neural activity and nodal topological measures of FC through simultaneous PET/MR measurement in 20 patients with MCI, 33 patients with AD, and 26 healthy individuals. First, we assessed regional glucose metabolism identified through FDG-PET (rFDG) (as a proxy of regional neural activity), and regional FC topology through clustering coefficient (CC) and degree centrality (DC) (as surrogates of local segregation and global connectivity, respectively). Next, we examined the potential moderating effect of disease status (AD or MCI) on the link between rFDG and FC topology using hierarchical moderated multiple regression analysis. Alterations in rFDG, CC, and DC were widespread in patients, and AD alters physiological coupling between regional metabolism and functional connectivity particularly in the inferior temporal gyus and supplementary motor areas. While rFDG correlated with CC in healthy subjects, this correlation was lost in AD patients. We suggest that AD pathology decouples the normal association between regional neural activity and functional segregation.

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bioRxiv2017

Amygdalar atrophy as the genetically mediated hub of limbic degeneration in Alzheimer’s disease

Pharmacological progress, basic science and medical practice can benefit from objective biomarkers that assist in early diagnosis and prognostic stratification of diseases. In the field of Alzheimers disease (AD), the clinical presentation of early stage dementia may not fulfill any diagnostic criteria for years, and quantifying structural brain changes by magnetic resonance imaging (MRI) has shown promise in the discovery of sensitive biomarkers. Although hippocampal atrophy is often used as an in vivo measure of AD, data-driven neuroimaging has revealed complex patterns of regional brain vulnerability that may not perfectly map to anatomical boundaries. In addition to aiding diagnosis, decoding genetic influences on neuroimaging measures of the disease can enlighten molecular mechanisms of the underlying pathology in living patients and guide the therapeutic design.\n\nHere, we aimed to extract a data-driven MRI feature of brain atrophy in AD by decomposing structural neuroimages using independent component analysis (ICA), a method for performing unbiased computational search in high dimensional data spaces. Our study of the AD Neuroimaging Initiative dataset (n=1,100 subjects) revealed a disease-vulnerable feature with a network-like topology, comprising amygdala, hippocampus, fornix and the inter-connecting white-matter tracts of the limbic system. Whole-genome sequencing identified a nonsynonymous variant (rs34173062) in SHARPIN, a gene coding for a synaptic protein, as a significant modifier of this new MRI feature (p=2.1x10-10). The risk variant was brought to replication in the UK Biobank dataset (n=8,428 subjects), where it was associated with reduced cortical thickness in areas co-localizing with those of the discovery sample (left entorhinal cortex p=0.002, right entorhinal cortex p=8.6x10-4; same direction), as well as with the history of AD in both parents (p=2.3x10-6; same direction).\n\nIn conclusion, our study shows that ICA can transform voxel-wise volumetric measures of the brain into a data-driven feature of neurodegeneration in AD. Structure of the limbic system, as the most vulnerable focus of brain atrophy in AD, is affected by genetic variability of SHARPIN. The elevated risk of dementia in carriers of the minor allele supports engagement of SHARPIN in the disease pathways, and its role in neurotransmitter receptor scaffolding and integrin signaling may inform on new molecular mechanisms of AD pathophysiology.\n\nAbbreviationsAlzheimers disease (AD), genome-wide association study (GWAS), independent component analysis (ICA), mild cognitive impairment (MCI), medial temporal circuit (MTC), single-nucleotide polymorphism (SNP), tensor-based morphometry (TBM)

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