Biology subjects

Asaad, W. F.

Publications and source records attributed to Asaad, W. F..

4 recordsLinked to original sources

bioRxiv2025

The temporal and perceptual characteristics of emotion-induced blindness

Attentional capture by emotionally salient stimuli is adaptive, permitting identification of possible threats; however, an excessive bias towards emotional stimuli can interrupt goal-directed behavior. This is especially relevant in psychiatric disease, where severe emotional distress can interfere with daily function. As such, understanding the mechanisms by which emotional stimuli compete for attentional resources is a critical area of investigation. Previous studies using rapid serial visual presentation (RSVP) paradigms observe that emotional distractors disrupt the detection of subsequent stimuli, referred to as emotion-induced blindness (EIB). Our study expands upon this work, characterizing how temporal and perceptual factors shape the emergence and intensity of EIB. Contrary to previous assumptions regarding temporal dynamics of EIB, we found that effects of emotional distractors persisted across prolonged image presentation durations. Further, we investigated the extent to which the depth of distractor processing influences EIB using a distractor recall task. While recall was predictive of EIB magnitude, a significant effect of emotional distractors on target detection was nonetheless present even without conscious recall of the distractor. These findings demonstrate the robustness of the EIB effect in RSVP in the context of temporal and perceptual manipulations.

neuroscience↗

bioRxiv2024

Distinct basal ganglia decision dynamics under conflict and uncertainty

The basal ganglia (BG) play a key role in decision-making, preventing impulsive actions in some contexts while facilitating fast adaptations in others. The specific contributions of different BG structures to this nuanced behavior remain unclear, particularly under varying situations of noisy and conflicting information that necessitate ongoing adjustments in the balance between speed and accuracy. Theoretical accounts suggest that dynamic regulation of the amount of evidence required to commit to a decision (a dynamic "decision boundary") may be necessary to meet these competing demands. Through the application of novel computational modeling tools in tandem with direct neural recordings from human BG areas, we find that neural dynamics in the theta band manifest as variations in a collapsing decision boundary as a function of conflict and uncertainty. We collected intracranial recordings from patients diagnosed with either Parkinsons disease (n=14) or dystonia (n=3) in the subthalamic nucleus (STN), globus pallidus internus (GPi), and externus (GPe) during their performance of a novel perceptual discrimination task in which we independently manipulated uncertainty and conflict. To formally characterize whether these task and neural components influenced decision dynamics, we leveraged modified diffusion decision models (DDMs). Behavioral choices and response time distributions were best characterized by a modified DDM in which the decision boundary collapsed over time, but where the onset and shape of this collapse varied with conflict. Moreover, theta dynamics in BG structures predicted the onset and shape of this collapse but differentially across task conditions. In STN, theta activity was related to a prolonged decision boundary (indexed by slower collapse and therefore more deliberate choices) during high-conflict situations. Conversely, rapid declines in GPe theta during low conflict conditions were related to rapidly collapsing boundaries and expedited choices, with additional complementary decision bound adjustments during high uncertainty situations. Finally, GPi theta effects were uniform across conditions, with increases in theta prolonging the collapse of decision bounds. Together, these findings provide a nuanced understanding of how our brain thwarts impulsive actions while nonetheless enabling behavioral adaptation amidst noisy and conflicting information.

neuroscience↗

bioRxiv2022

Decoding Dynamically Shifting States of Parkinson's Disease: Tremor, Bradykinesia, and Effective Motor Control

Parkinsons Disease (PD) is characterized by distinct motor phenomena that are expressed asynchronously. Understanding the neurophysiological correlates of these different motor states could facilitate monitoring of disease progression and allow improved assessments of therapeutic efficacy, as well as enable optimal closed-loop neuromodulation. We examined neural activity in the basal ganglia and cortex of subjects with PD during a quantitative motor task to decode tremor and bradykinesia -- two cardinal motor signs of this disease -- and relatively asymptomatic periods of behavior. Analysis of subcortical and cortical signals revealed that tremor and bradykinesia had distinct, nearly opposite neural signatures, while effective motor control displayed unique, differentiating features. The neurophysiological signatures of these motor states depended on the type of signal recorded as well as the location; cortical decoding accuracy generally outperformed subcortical decoding, while tremor and bradykinesia were better decoded from different portions of the subthalamic nucleus (STN). These results provide a roadmap to leverage real-time neurophysiology to understand and treat PD. One Sentence SummaryMotor signs of Parkinsons disease such as tremor and bradykinesia can be independently decoded from subthalamic and cortical recordings.

neuroscience↗

bioRxiv2019

Modeling mechanisms of tremor reduction for essential tremor using symmetric biphasic DBS

Essential tremor (ET) is the most common movement disorder, in which the primary symptom is a prominent, involuntary 4-10 Hz movement. For severe, medication refractory cases, deep brain stimulation (DBS) targeting the ventral intermediate nucleus of the thalamus (VIM) can be an effective treatment for cessation of tremor and is thought to work in part by disrupting tremor frequency oscillations (TFOs) in VIM. However, DBS is not universally effective and may be further disrupting cerebellar-mediated activity in the VIM. Here, we applied biophysically detailed computational modeling to investigate whether the efficacy of DBS is affected by the mechanism of generation of TFOs or by the pattern of stimulation. We simulated the effects of DBS using standard, asymmetric pulses as well as biphasic, symmetric pulses to understand biophysical mechanisms of how DBS disrupts TFOs generated either extrinsically or intrinsically. The model results suggested that the efficacy of DBS in the VIM is affected by the mechanism of generation of TFOs. Symmetric biphasic DBS reduced TFOs more than standard DBS in both networks, and these effects were stronger in the intrinsic network. For intrinsic tremor frequency activity, symmetric biphasic DBS was more effective at reducing TFOs. Simulated non-tremor signals were also transmitted during symmetric biphasic DBS, suggesting that this type of DBS may help to reduce side effects caused by disruption of the cerebellothalamocortical pathway. Biophysical details in the model provided a mechanistic interpretation of the cellular and network dynamics contributing to these effects that can be empirically tested in future studies.\n\nSignificance StatementEssential tremor (ET) is a common movement disorder, whose primary symptom is an involuntary rhythmic movement of the limbs or head. An area of the human tha-lamus demonstrates electrical activity that oscillates at the frequencies of tremor, and deep brain stimulation (DBS) in this area can reduce tremor. It is not fully understood how DBS affects tremor frequency activity in the thalamus, and studying different patterns of DBS stimulation may help to clarify these mechanisms. We created a computational model of different shapes of DBS and studied how they reduce different hypothesized generators of tremor frequency activity. A greater understanding of how DBS affects the thalamus may lead to improved treatments to reduce tremor and alleviate side effects in patients with ET.

neuroscience↗