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Our research lies at the intersection of cognitive neuroscience and neuroengineering, driven by a deep curiosity about how the brain supports higher-order cognitive functions such as memory, attention, and cognitive control. We are particularly interested in understanding the dynamic neural mechanisms—spanning oscillatory activity, network connectivity, and neuromodulatory systems—that enable these processes. To this end, we combine non-invasive brain stimulation (TMS, tES, and ultrasound), neuroimaging (fMRI, EEG), and computational approaches to causally probe and modulate cognitive networks. A central theme of our work is using brain stimulation not just as a tool for intervention, but as a method for uncovering the causal architecture of cognition. Our recent efforts have focused on developing closed-loop, biomarker-informed stimulation protocols to enhance memory and executive function in healthy individuals. Ultimately, our goal is to bridge mechanistic neuroscience with translational applications, advancing precision neuromodulation as a means of understanding and optimizing human cognition.
Personalized Brain Stimulation Improves Working Memory
Transcranial magnetic stimulation (TMS) is a non-invasive way to stimulate the brain and has shown promise in treating various mental health and cognitive conditions. However, one major challenge is that its effects can vary a lot from person to person. This study set out to make TMS more effective by tailoring it to each individual's brain.
Using brain scans (fMRI), researchers first mapped out each participant’s unique brain network involved in memory. They then used artificial intelligence to help guide where and how to stimulate the brain in real time during a memory task. Participants received TMS at different settings while their brain activity and performance were monitored. The system used this information to identify the best (and worst) stimulation settings for each person.
Later, participants went through six sessions of brain stimulation, three with their "optimal" setting and three with the "suboptimal" one while doing memory and control tasks. The results showed that the personalized, optimal stimulation improved performance on the memory task over time, while the suboptimal setting and the control task showed no such improvement.
In short, this study shows that using AI and brain imaging to personalize TMS can lead to better brain stimulation outcomes. It’s an exciting step toward smarter, more effective treatments for the brain.
Can Brain Stimulation Help Us Forget Less?
When we try to remember something, like an item on a grocery list, it can surprisingly make us forget other, related memories, such as another item name from the same grocery list. This everyday quirk of memory is called "retrieval-induced forgetting," and it happens because your brain actively suppresses competing information to help you focus on what you're trying to recall. Our study found a way to dial down this suppression using a safe, non-invasive brain stimulation technique called tDCS, targeting a region called the medial prefrontal cortex.
Fifty volunteers either received real stimulation or a sham version while practicing memory recall, and those who got the real stimulation remembered significantly more of the "competing" memories that would normally get pushed aside. Importantly, this boost didn't come at any cost, their memory for the actively practiced material stayed just as strong.
Using EEG, we traced this effect to specific brain-wave changes: an early shift in the prefrontal cortex within half a second of trying to recall something, which then triggered related activity in the parietal cortex a moment later, a region known to support successful memory retrieval. Together, these results reveal a specific brain circuit involved in actively suppressing memories, and show that stimulating it can partially unlock memories we'd otherwise lose.
Beyond satisfying scientific curiosity, this work could inform future treatments for conditions involving problematic memory suppression or intrusion, such as helping people retain more of what they learn, or potentially aiding those struggling with intrusive memories in PTSD.
Published in Journal of Neuroscience (2024)
Bridging Brainwaves and Memories: The Potential of Non-Invasive Stimulation
Episodic memory is our ability to remember past experiences, like recalling a fun birthday or a trip you took. This kind of memory relies on specific parts of the brain, especially an area called the hippocampus and other connected regions in the front and side of the brain. Scientists want to understand how these different brain areas work together to help us form, store, and recall these memories. A special tool called transcranial magnetic stimulation (TMS) allows researchers to gently stimulate certain brain areas without surgery. This helps them see how changing brain activity in specific spots affects memory, giving clues about which parts of the brain are important for remembering. This review talks about how our understanding of episodic memory has grown and how TMS is being used to study and potentially improve memory by targeting key brain areas. It also discusses what this means for future research into how memories work in the brain
Published in Neuroscience Bulletin (2025)
Electric Boost: Enhancing Cognitive Control Through Brain Stimulation
This study investigated the effects of transcranial direct current stimulation (tDCS) applied to the anterior cingulate cortex (ACC), a key region involved in cognitive control. Using resting-state fMRI and a Stroop task, the researchers measured changes in functional connectivity and behavioral performance in 20 participants receiving either active or sham stimulation.
Results showed that active tDCS reduced resting-state connectivity between the ACC and several right-hemisphere cortical areas and was associated with faster reaction times on the Stroop task. Moreover, changes in connectivity correlated positively with behavioral improvements.
These findings indicate that ACC stimulation modulates brain network dynamics, enhancing cognitive control and suggesting the ACC as a promising target for cognitive enhancement interventions.
Peer-Reviewed Journal Publications
Peer-Reviewed Journal Publications
Ahsan Khan, Hongming Li, Camille Blaine, Julie Grier, Ethan Hammett, Almaris Figueroa-Gonzalez, Sarai Garcia, Romain Duprat, Justin Reber, Joseph Deluisi, Christos Davatzikos, Theodore D Satterthwaite, Yong Fan, Desmond J Oathes (2026). Personalized Network-Guided Neuromodulation Enhances Human Working Memory. Advanced Science. URL
Ahsan Khan, Desmond J. Oathes (2025). Brainwaves Meet Soundwaves: Ultrasound Stimulation for Treating Major Depressive Disorder by Targeting the Subcallosal Cingulate Cortex. Neuropsychopharmacology. URL
Ahsan Khan, Jing Liu, Maite Crespo Garcia, Kai Yuan, ChengPeng Hu, Ziyin Ren, Chun Hang Eden Ti, Raymond Kai-Yu Tong (2025). From Correlation to Causation: Understanding Episodic Memory Networks. Neuroscience Bulletin. URL
Ahsan Khan, Chun Hang Eden, Kai Yuan, Maite Crespo Garcia, Michael C. Anderson, Kai-Yu Tong (2024). Medial Prefrontal Cortex Stimulation Reduces Retrieval-Induced Forgetting via Fronto-Parietal Beta Desynchronization. The Journal of Neuroscience. URL
Ahsan Khan, Jochen A. Mosbacher, Stephan Vogel, Mira Binder, Michael Wehovz, Arnulf Moshammer, Stefan Halverscheid, Kolja Pustelnik, Michael A. Nitsche, Kai-Yu Tong, Roland H. Grabner (2023). Modulation of Resting-State Networks Following Repetitive Transcranial Alternating Current Stimulation of the Dorsolateral Prefrontal Cortex. Brain Structure and Function. URL
Ahsan Khan, Cheng Chen, Kai Yuan, Kai-Yu Tong (2022). Impact of Anodal High-Definition Transcranial Direct Current Stimulation of Medial Prefrontal Cortex on Stroop Task Performance and Its Electrophysiological Correlates: A Pilot Study. Neuroscience Research. URL
Ahsan Khan, Xin Wang, Chun Hang Eden, Kai-Yu Tong (2020). Anodal Transcranial Direct Current Stimulation of Anterior Cingulate Cortex Modulates Subcortical Brain Regions Resulting in Cognitive Enhancement. Frontiers in Human Neuroscience. URL
Ahsan Khan, Cheng Chen, Kai Yuan, Xin Wang, Prabhav Mehra, Yunmeng Liu, Raymond Kai-Yu Tong (2020). Changes in EEG Complexity and fMRI Connectivity Following Robotic Hand Training in Chronic Stroke. Topics in Stroke Rehabilitation. URL
Ahsan Khan†, Kai Yuan†, Shi-Chun Bao, Chun Hang Eden, Abdullah Tariq, Nimra Anjum, Raymond Kai-Yu Tong (2022). Can Transcranial Electrical Stimulation Facilitate Post-Stroke Cognitive Rehabilitation? A Systematic Review and Meta-Analysis. Frontiers in Rehabilitation Sciences. URL
Xinyu Li†, Ahsan Khan†, Yingying Li, Diansen Chen, Jing Yang, Haohui Zhan, Ganqin Du, Jin Xu, Wutao Lou, Kai-Yu Tong (2021). Hyperconnection and Hyperperfusion of Overlapping Brain Regions in Patients with Menstrual-Related Migraine: A Multimodal Neuroimaging Study. Neuroradiology. URL
Shi-Chun Bao, Ahsan Khan, Rong Song, Kai-Yu Tong (2020). Rewiring the Lesioned Brain: Electrical Stimulation for Post-Stroke Motor Restoration. Journal of Stroke (JoS). URL
Kai Yuan, Cheng Chen, Ahsan Khan, Kai-Yu Tong (2022). Heterogeneous Stimulation Effects of Alpha and Beta Band Stimulation in Chronic Stroke: A Concurrent tACS-fMRI Study. IEEE Transactions on Neural Systems & Rehabilitation Engineering. URL
Cheng Chen, Kai Yuan, Xin Wang, Ahsan Khan, Chiu-wing Chu, Kai-Yu Tong (2021). Neural Correlates of Motor Recovery After Robot-Assisted Training in Chronic Stroke: A Multimodal Neuroimaging Study. Neuroplasticity. URL
Chengpeng Hu, Chun Hang Eden Ti, Kai Yuan, Cheng Chen, Ahsan Khan, Xiangqian Shi, Winnie Chiu-wing Chu, Raymond Kai-Yu Tong (2024). Multisite Stimulation on Shifted Motor Hotspots with EMG-Driven Robotic Hand Improves Upper Extremity Motor Function and Neuromuscular Control in Chronic Stroke: A Randomized Controlled Trial. IEEE Transactions on Neural Systems & Rehabilitation Engineering. URL
Undergraduate Student Projects
Mood-Induced Affective Blunting During Memory Encoding: EEG Evidence and Mindfulness Modulation (2025-26)
Hayley & Jasmin
Mood states strongly influence episodic memory processing, yet the neural mechanisms through which mood interacts with stimulus valence during encoding remain unclear. This study examined how experimentally induced negative mood would modulate neural processing and behavioural outcomes during an associative memory task, and whether mindfulness intervention can alter these effects. Findings show that negative mood undermines associative binding and influences early stages of visual-affective processing, while mindfulness may primarily positively influence the associated affective responses.
The Effect of Inhibitory Control Training via GO/NO GO Task on Food Choice and Neural Correlates in Young Adults (2025-26)
Rainer & Elma
Previous behavioral studies demonstrate that No-Go training can reduce food liking and consumption, the neural mechanisms underlying food devaluation remain poorly understood, particularly in terms of temporal dynamics. Few studies have leveraged EEG to assess how inhibitory training modifies neural responses to food stimuli. The present study investigates whether repeated response inhibition toward food stimuli through a Go/No-Go training paradigm leads to stimulus devaluation. Using EEG, the study further examines the neural mechanisms through which inhibitory training alters food valuation.
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