A cross-disciplinary team from The Hong Kong University of Science and Technology (HKUST) has developed a breakthrough laser control technique designed to eliminate crosstalk in brain imaging and stimulation. Led by Professor Qu Jianan of the Department of Electronic and Computer Engineering and Professor Julie L. Semmelhack from the Division of Life Science, the researchers created a method functioning as a smart dimmer for neural circuits. Their study, titled Active pixel power control for crosstalk-free all-optical neural interrogation, was published in Nature Communications. All-optical interrogation allows scientists to observe and control specific neurons using genetically encoded sensors and optogenetic actuators. While this approach offers high speed and precision, a significant challenge has persisted: infrared lasers used for imaging can inadvertently activate neurons, creating experimental artifacts known as crosstalk. This phenomenon makes it difficult to distinguish between natural brain activity and interference caused by the imaging process itself. To solve this, the team introduced Active Pixel Power Control (APPC). This strategy acts as a real-time dimmer switch for individual scanning pixels. Guided by custom mapping software that identifies where light-sensitive proteins are expressed, a fast acousto-optic modulator dynamically adjusts the laser power at each pixel. The system delivers reduced or zero power to specific neurons while maintaining uniform light intensity in other regions. This ensures that neurons intended for stimulation are not disrupted by imaging light, and neighboring neurons remain unaffected by the recording process. The researchers validated the technology using larval zebrafish, which share over 70% genetic similarity with the human brain. In vivo tests demonstrated that APPC successfully preserved signal quality while suppressing optogenetic artifacts and significantly reducing crosstalk. A key advantage of the new method is its compatibility with standard two-photon microscopes used globally. Unlike previous solutions that required complete system overhauls, APPC can be integrated into existing equipment, making it a cost-effective and practical advancement for neuroscience laboratories. Professor Qu noted that while all-optical approaches hold great promise for investigating how brain circuits drive behavior, crosstalk has been a major barrier to their accuracy. He stated that APPC brings researchers closer to observing brain function under natural physiological conditions by solving one of the most significant technical roadblocks. Professor Semmelhack added that the study exemplifies the power of collaboration between engineering and biology. She emphasized that the method integrates precision optics with in vivo circuit neuroscience, paving the way for other research groups to explore brain mechanisms and pathologies more effectively. This innovation is expected to drive research into the mechanisms of brain diseases and facilitate the development of small animal disease models for new drug treatments. By ensuring that neural manipulation remains precise and free from unintended interference, the technique opens new avenues for understanding complex neural functions and developing targeted therapies for neurological disorders.