Biology subjects

Abbaszadeh, M.

Publications and source records attributed to Abbaszadeh, M..

6 recordsLinked to original sources

bioRxiv2024

Spatially Enhanced Processing for Valuable Objects in Prefrontal Cortex Neurons During Efficient Search

It is recently shown that objects with long-term reward associations can be efficiently located during visual search. The neural mechanism for valuable object pop-out is unknown. In this work, we recorded neuronal responses in the ventrolateral prefrontal cortex (vlPFC) with known roles in visual search and reward processing in macaques while monkeys engaged in efficient vs inefficient visual search for high-value fractal objects (targets). Behavioral results and modeling using multi-alternative attention-modulated drift-diffusion (MADD) indicated that efficient search was concurrent with enhanced processing for peripheral objects. Notably, neural results showed response amplification and receptive field widening to peripherally presented targets in vlPFC during visual search. Both neural effects predict higher target detection and were found to be correlated with it. Our results suggest that value-driven efficient search independent of low-level visual features arises from reward-induced spatial processing enhancement of peripheral valuable objects.

neuroscience↗

bioRxiv2024

Prefrontal cortex temporally multiplexes slow and fast dynamics in value learning and memory

Previous studies have revealed segregated circuitries in basal ganglia for fast learning that enables value adaptability and slow forgetting which underlies stable value memories. However, the mechanisms mediating the conflict between value adaptability vs stability remain unknown. Using a reinforcement learning paradigm involving a brief value reversal for objects with previously stable values, we predicted and confirmed a novel behavioral manifestation of the conflict between adaptability vs stability namely the spontaneous recovery of old values in macaque monkeys. Furthermore, we found that individual neurons in ventrolateral prefrontal cortex (vlPFC) temporally multiplexed slow and fast processes in their early and late responses to objects. The local field potential in vlPFC also reflected the two-rate system. These findings implicate vlPFC as a plexus for the interactions between adaptability vs stability in reinforcement learning and suggest spontaneous recovery of past values caused by a two-rate system to mediate relapse to old habits.

neuroscience↗

bioRxiv2023

Time Course of Dual-task Interference in the Brain in Simulated Driving Environment

Due to the brains limited cognitive capacity, simultaneous execution of multiple tasks can lead to performance impairments, mainly when the tasks occur closely in time. This limitation is known as dual-task interference. We aimed to investigate the time course of this phenomenon in the brain, utilizing a combination of EEG, multivariate pattern analysis (MVPA), and drift-diffusion modeling (DDM). Here, participants first performed a tone discrimination task, followed by a lane-change task with either short or long onset time differences (Stimulus Onset Asynchrony, SOA), in a simulated driving environment. As expected, the dual-task interference increased the second tasks (lane-change) reaction time. The DDM analysis indicated that this increase was attributable to changes in both the decision time and the post-decision time. Our MVPA findings revealed a decrease in decoding accuracy for the lane-change task in short SOA compared to both long SOA and single-task conditions throughout the trial, highlighting the presence of interference. Moreover, the temporal generalization analysis identified a significant interference effect in short SOA compared to long SOA and single-task conditions after [~]250 ms relative to stimulus onset. Additionally, the conditional generalization analysis showed a delayed response after [~]450 ms. Searchlight analysis illustrated the progression of this information reduction, starting in occipital, parietal, and parieto-occipital leads responsible for perceptual and central processing and then transferring to the frontal leads for mapping decisions onto motor actions. Consistent with the hybrid dual-task interference theory, our results suggest that the processing of the two tasks occurs in a partial parallel manner for the first few hundred milliseconds and primarily in the perceptual and decision-processing stages. Subsequently, another competition arises between the two tasks to route information to motor areas for execution, resulting in the second tasks serial processing and delay or lengthening.

neuroscience↗

bioRxiv2023

Value-based search efficiency is encoded in substantia nigra reticulata firing rate, spiking irregularity and local field potential

Recent results show that valuable objects can pop-out in visual search yet its neural mechanisms remain unexplored. Given the role of substantia nigra reticulata (SNr) in object value memory and control of gaze, we recorded its single unit activity while male macaque monkeys engaged in efficient or inefficient search for a valuable target object among low-value objects. Results showed that efficient search was concurrent with stronger inhibition and higher spiking irregularity in target present (TP) compared to target absent (TA) trials in SNr. Importantly, the firing rate differentiation of TP and TA trials happened within [~]100ms of display onset and its magnitude was significantly correlated with the search times and slopes (aka search efficiency). Time-frequency analyses of local field potential (LFP) after display onset revealed significant modulations of gamma band power with search efficiency. The greater reduction of SNr firing in TP trials in efficient search can create a stronger disinhibition of downstream superior colliculus which in turn can facilitate saccade to obtain valuable targets in competitive environments. Significant statementMost times we have to find a few relevant or highly valued objects among many objects that surround us. When our target objects are not distinct from their surroundings based on low-level features, searching for them becomes tedious and slow. Nevertheless, recent findings show that valuable objects can be found efficiently and fast if they have been repeatedly paired with reward. Our results show that the rate and pattern of spiking as well as local voltage fluctuations in the basal ganglia output which is known to control attention and saccade correlate with such value-driven search efficiency. Thus, in addition to reward learning, basal ganglia can have a role in skillful interactions with and rapid detection of rewarding objects.

neuroscience↗

bioRxiv2023

Prefrontal Cortex Encodes Value Pop-out in Visual Search

Recent evidence shows that long-term object value association can lead to efficient visual search. However, the neural mechanism of this value pop-out has yet to be understood. Given the known role of the ventrolateral prefrontal cortex (vlPFC) in visual search and value memory, we recorded its single-unit activity (n=526) in two macaque monkeys while they engaged in the value-driven search. Monkeys had to determine whether a high-value target was present within a variable number of low-value objects. Interestingly, differential neural firing, as well as gamma-band power, indicated the presence of a target within [~]150ms of display onset. This differential activity was negatively correlated with search time and became less display size-dependent for more efficient searches. On the other hand, neural firing and its variability were higher in inefficient searches. These findings reveal the neural code within vlPFC for rapid detection of valuable targets, which can be crucial for animals faced with competition. Significance StatementSearch for rewarding objects is ubiquitous and crucial for animals and humans alike. Up until recently, it was thought that visual search for valuable targets that were otherwise not distinct by low-level features should be serial and slow. Contrary to this belief, we showed that given sufficient reward training, valuable objects can be found efficiently in search suggesting a value pop-out neural mechanism. Importantly, we reveal the neural activity in the prefrontal cortex (PFC) to be predictive of the degree of value-driven search efficiency. Given the role of PFC in object value memory, these results show how PFC can translate such memories to emulate the parallel processing of visual information independent of low-level visual features.

neuroscience↗

bioRxiv2023

Colorimetric Detector for Hydrogen Sulfide Detection in Industrial Environments Based on Silver Nanoparticles Synthesized in Streptomyces Bacteria

Hydrogen sulfide is a colorless, foul-odor pollutant with corrosive properties. This gas is one of the important pollutants released from food factories, fertilizer manufacturing factories, sewage treatment plants, and well drilling. Considering the dangers of being exposed to hydrogen sulfide gas, this article provides a cost-effective, simple, life-saving efficient solution. In this study, Streptomyces bacterium was used for biological production of silver nanoparticles, due to its resistance to the antimicrobial properties of silver. The synthesis and the size range of nanoparticles were confirmed using validation methods. For preparing biocomposite that entraps biological agents, microencapsulation of bacteria was adopted using gellan gum and alginate. In order to validate the final product, the viscosity and porosity of the biocomposite were determined. These tests aimed to investigate the mechanical properties affecting the behaviour and the response time of the final detector. In the end, the detector was exposed to hydrogen sulfide gas, and the color changes of the detector were recorded by time. According to the results, the control sample remained unchanged in all concentrations. However, the color of the test sample, changed faster with the increase in the input gas concentration. Moreover, no color change was observed in concentrations less than 20 mg/l. Therefore, the designed biodetector can be used for qualitative and semi-quantitative measurement of Hydrogen sulfide, in concentrations higher than 20 mg/l.

bioengineering↗