Biology subjects

Baker, T. E.

Publications and source records attributed to Baker, T. E..

9 recordsLinked to original sources

bioRxiv2026

Precision phase targeting of event-related oscillations using real-time closed-loop TMS-EEG

ObjectiveCurrent closed-loop TMS-EEG systems rely on phase prediction algorithms that require highly periodic signals, limiting their ability to target brief, event-related activity. We developed a real-time closed-loop (RT-CL) TMS-EEG system that directly detects oscillatory phase without prediction, enabling phase-locked stimulation within microseconds. MethodsWe validated the system against a prediction-based approach using simulated sine waves and human EEG data (N=18), without active TMS delivery. ResultsAcross frequency-modulated sweeps and spontaneous occipital alpha oscillations (eyes-open vs. closed), the RT-CL system achieved higher triggering probability (11-24%) and reduced the phase error variability (2-10{degrees}). Importantly, when targeting event-related theta oscillations during two spatial navigation tasks, RT-CL produced [~]20% higher triggering probabilities and [~]17{degrees} lower phase error variability than phase prediction. ConclusionThese findings validate the RT-CL system for probing phase-dependent mechanisms during active cognition and pathological brain states. SignificanceBy precisely targeting brief, variable neural signals, RT-CL could be used for the development of personalized TMS interventions for neuropsychiatric disorders during symptom provocation.

neuroscience↗

bioRxiv2026

Right posterior theta facilitates memory encoding and recall during virtual navigation

Despite decades of animal and human intracranial work highlighting the critical role theta oscillations (4-12 Hz) play in memory encoding and recall stage during navigation, the link between scalp recorded human theta oscillations and spatial encoding and recall is lacking. In the present study, we used right posterior theta (RPT) - a scalp-level theta signal believed to be generated in the medial temporal cortex - to examine spatial encoding and recall during virtual spatial navigation. In particular, we recorded EEG from 27 healthy subjects performing a novel virtual Linear Track Memory (LTM) task. During the encoding stage of the task, a reward cue was presented at one of five pillar locations along a linear track. During the recall stage, subjects were presented with images of the five pillars and five new pillars, and were asked to press a button when the rewarded target pillar location appeared. If correct, subjects received 5 cents for that trial. Memory performance was assessed using reaction time, d-prime (d), and response bias ({beta}), and RPT was measured following the onset of the reward cue at bilateral scalp electrodes P7 and P8. Consistent with previous work, RPT peaked approximately 170-300 ms over the right hemisphere (P8) after cue onset, which was significantly increased for reward cues during the encoding stage and for the target pillar during the recall stage. Importantly, general linear model regressions revealed that peak RPT power during the encoding stage significantly predicted higher d and {beta} scores during recall, supporting the relationship between RPT peak power and memory performance. Together, these findings support the proposal that RPT activity reflects the encoding of salient information for the purpose of spatial navigation and a promising candidate biomarker for memory-related functioning in health and disease (e.g., Alzheimers disease).

neuroscience↗

bioRxiv2024

Right posterior theta reflects human parahippocampal phase resetting by salient cues during goal-directed navigation

Animal and computational work indicate that phase resetting of theta oscillations (4-12 Hz) in the parahippocampal gyrus (PHG) by salient events (e.g., reward, landmarks) facilitates the encoding of goal-oriented information during navigation. Although well-studied in animals, this mechanism has not been empirically substantiated in humans. In the present article, we present data from two studies (Study 1: asynchronous EEG-MEG | Study 2: simultaneous EEG-fMRI) to investigate theta phase resetting and its relationship to PHG BOLD activation in healthy adults (aged 18-34 years old) navigating a virtual T-maze to find rewards. In the first experiment, both EEG and MEG data revealed a burst of theta power over right-posterior scalp locations following feedback onset (termed right-posterior theta, RPT), and RPT power and measures of phase resetting were sensitive to the subjects spatial trajectory. In Experiment 2, we used probabilistic tractography data from the human connectome project to segment the anterior and posterior PHG based on differential connectivity profiles to other brain regions. This analysis resulted in a PHG subdivision consisting of four distinct anterior and two posterior PHG clusters. Next, a series of linear mixed effects models based on simultaneous EEG-fMRI data revealed that single-trial RPT peak power significantly predicted single-trial hemodynamic responses in two clusters within the posterior PHG and one in the anterior PHG. This coupling between RPT power and PHG BOLD was exclusive to trials performed during maze navigation, and not during a similar task devoid of the spatial context of the maze. These findings highlight a role of PHG theta phase resetting for the purpose of encoding salient information during goal-directed spatial navigation. Taken together, RPT during virtual navigation integrates experimental, computational, and theoretical research of PHG function in animals with human cognitive electrophysiology studies and clinical research on memory-related disorders such as Alzheimers disease.

neuroscience↗

bioRxiv2024

Blunted anterior midcingulate response to reward in opioid users is normalized by prefrontal transcranial magnetic stimulation

IntroductionAbnormalities in goal-directed behavior, mediated by mesocorticolimbic reward function and structure, contribute to worse clinical outcomes including higher risk of treatment dropout and drug relapse in opioid users (OU). Material and MethodIn a sham-controlled randomized study design, we measured whether robot-assisted 10Hz transcranial magnetic stimulation (TMS) applied to the prefrontal cortex was able to modulate anterior midcingulate cortex (MCC) electrophysiological response to rewards, in OU and matched healthy controls. ResultsWe show that OU exhibit a blunted anterior MCC reward response, compared to healthy controls (t(39) = 2.62, p = 0.01, d = 0.84), and that this is normalized following 10-Hz excitatory TMS (t(36) = .82, p = 0.42, d = 0.17). ConclusionsExcitatory TMS modulated the putative reward function of the MCC in OU. Further work with increased sample sizes and TMS sessions is required to determine whether restoring MCC reward function increases reward-directed behaviors, which may enhance treatment success through the maintenance of treatment goals.

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bioRxiv2023

Oscillatory correlates of threat imminence during virtual navigation

The Predator Imminence Theory proposes that defensive behaviors depend on the proximity of a threat. While the neural mechanisms underlying this proposal have been well studied in animal models, it remains poorly understood in humans. To address this issue, we recorded EEG from twenty-four (15 female) young adults engaged in a first-person virtual reality Risk-Reward Interaction task. On each trial, participants were placed in a virtual room and then presented with either a threat or reward conditioned stimulus (CS) in the same room location (proximal) or different room location (distal). At a behavioral level, all participants learned to avoid the threat-CS, with most using the optimal behavior to actively avoid the proximal threat-CS (88% accuracy) and passively avoid the distal threat-CS (69% accuracy). By contrast, participants learned to actively approach the distal reward-CS (82% accuracy) and to remain still (passive) to the proximal reward-CS (72% accuracy). At an electrophysiological level, we observed a general increase in theta power (4-8 Hz) over right posterior channel P8 across all CS conditions, with the proximal threat-CS evoking the largest theta response. By contrast, distal CS cues induced two bursts of gamma (30-60 Hz) power over midline-parietal channel Pz (approx. 200 msec post-cue) and right frontal channel Fp2 (approx. 300 msec post-cue). Interestingly, while both bursts were sensitive to distal-CS cues, the first burst of gamma power was sensitive to the distal threat-CS requiring a passive response, and the second burst at channel Fp2 was sensitive to the distal reward-CS requiring an active response. Together, these findings demonstrate that oscillatory processes differentiate between the spatial proximity information during threat and reward encoding, likely optimizing the selection of the appropriate behavioral response.

neuroscience↗

bioRxiv2023

Recording neural reward signals in the real-world using mobile-EEG and augmented reality

The electrophysiological response to rewards recorded during laboratory-based tasks has been well documented over the past two decades, yet little is known about the neural response patterns in real-world settings. To address this issue, we combined a mobile-EEG system with an augmented reality headset (which blends high definition "holograms" within the real-world) to record event-related brain potentials (ERP) while participants navigated an operant chamber to find rewards. 25 participants (age = 18-43, Male=6, Female=19) were asked to choose between two floating holograms marking a west or east goal-location in a large room, and once participants reached the goal location, the hologram would turn into a reward (5 cents) or no-reward (0 cents) cue. Following the feedback cue, participants were required to return to a hologram marking the start location, and once standing in it, a 3 second counter hologram would initiate the next trial. This sequence was repeated until participants completed 200 trials. Consistent with previous research, reward feedback evoked the reward positivity, an ERP component believed to index the sensitivity of the anterior cingulate cortex to reward prediction error signals. The reward positivity peaked around 235ms post-feedback with a maximal at channel FCz (M=-2.60V, SD=1.73V) and was significantly different than zero (p < 0.01). At a behavioral level, participants took approximately 3.38 seconds to reach the goal-location and exhibited a general lose-shift (68.3% {+/-} 3.5) response strategy and were slightly slower to return to the start location following negative feedback (2.43 sec) compared to positive feedback (2.38 sec), evidence of post-error slowing. Overall, these findings provide the first evidence that combining mobile-EEG with augmented reality technology is a feasible solution to enhance the ecological validity of human electrophysiological studies of goal-directed behavior and a step towards a new era of human cognitive neuroscience research that blurs the line between laboratory and reality.

neuroscience↗

bioRxiv2022

Causal effects of prefrontal transcranial magnetic stimulation on dopamine-mediated reinforcement learning in healthy adults

Background10-Hz repetitive transcranial magnetic stimulation (rTMS) to the left dorsal lateral prefrontal cortex (DLPFC) has been shown to increase dopaminergic activity in the dorsal striatum, a region strongly implicated in reinforcement learning. However, the behavioural influence of this effect remains largely unknown. ObjectiveHere, we tested the causal effects of rTMS on behavioral and computational characteristics of reinforcement learning. Methods40 healthy individuals were randomized into Active and Sham rTMS groups. Each participant underwent one 10-Hz rTMS session (1500 pulses) in which stimulation was applied over the left DLPFC using a robotic arm. Participants then completed a reinforcement learning task sensitive to striatal dopamine functioning. Participants trial-to-trial training choices were modelled using a reinforcement learning model (Q-learning) that calculates separate learning rates associated with positive and negative reward prediction errors. ResultsSubjects receiving Active TMS exhibited an increased reward rate (number of correct responses per second of task activity) compared to the Sham rTMS group. Computationally, the Active rTMS group displayed a higher learning rate for correct trials (G) compared to incorrect trials (L). Finally, when tested with novel pairs of stimuli, the Active group displayed extremely fast reaction times, and a trend towards a higher reward rate. ConclusionsThe present study provided specific behavioral and computational accounts of altered striatal-mediated reinforcement learning induced by a proposed increase of dopamine activity by 10-Hz rTMS to the left DLPFC. Together, these findings bolster the use of TMS to target neurocognitive disturbances attributed to the dysregulation of dopaminergic-striatal circuits.

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bioRxiv2021

Power dynamics of theta oscillations during goal-directed navigation in freely moving humans: A mobile EEG-virtual reality T-maze study

Theta oscillations ([~]4-12 Hz) are dynamically modulated by speed and direction in freely moving animals. However, due to the paucity of electrophysiological recordings of freely moving humans, this mechanism remains poorly understood. Here, we combined mobile-EEG with fully immersive virtual-reality to investigate theta dynamics in twenty-two healthy adults (aged 18-29 years old) freely navigating a T-maze to find rewards. Our results revealed three dynamic periods of theta modulation: 1) theta power increases coincided with the participants decision-making period; 2) theta power increased for fast and leftward trials as subjects approached the goal location; and 3) feedback onset evoked two phase-locked theta bursts over the right temporal and frontal-midline channels. These results suggest that recording scalp EEG in freely moving humans navigating a simple virtual T-maze can be utilized as a powerful translational model by which to map theta dynamics during "real-life" goal-directed behavior in both health and disease.

neuroscience↗

bioRxiv2019

Beyond the Motor Cortex: Theta Burst Stimulation of the Anterior Midcingulate Cortex

Intermittent Theta Burst Stimulation (TBS) applied to the left dorsolateral prefrontal cortex suppressed reward-related signaling in the anterior midcingulate cortex (aMCC), resulting in a change in goal-directed behavior. Continuous TBS had no effect. While these results are inconsistent with reported TBS effects on motor cortex, the present findings offer normative insights into the magnitude and time course of TBS-induced changes in aMCC excitability during goal-directed behavior.

neuroscience↗