"Unraveling the Unknown Territory of the Brain"… How the Brain Integrates Visual and Auditory Signals

We see, feel, and move every day. And with every movement, our brain operates through an invisible and intricate mechanism. This complex signaling system of the brain remains one of the final frontiers in science—an area still not fully understood.

The Center for Synaptic Brain Dysfunctions within the Institute for Basic Science (IBS) is working to decode how the brain functions, with a focus on identifying the core mechanisms behind brain disorders such as ADHD and autism, and exploring how these conditions might be treated. In March, the team published findings from an animal study showing that the brain integrates sensory information differently depending on behavioral state, shedding light on the mechanism of sensory integration in the brain.

Dr. CHOI Il Song, a postdoctoral researcher at the Center for Synaptic Brain Dysfunctions who participated in the study, said, “The research began with a simple question: Could the movement state of an animal affect how visual and auditory information are integrated, perhaps altering the brain’s sensory priorities?” He continued, “Our findings show that an animal's locomotion state indeed influences how the brain integrates visual and auditory signals, particularly by adjusting the priority given to different sensory inputs.”

We sat down with Dr. Choi—who entered neuroscience in pursuit of an answer to the question, “Where do thoughts come from?”—to hear more about the significance of this research and his future goals.

Q. Please introduce yourself.

Hello, my name is CHOI Il Song, and I am a postdoctoral researcher in the lab of Associate Director LEE Seung-Hee of the Center for Synaptic Brain Dysfunctions within the IBS. I earned my Ph.D. in Biological Sciences from KAIST under Dr. Lee’s supervision, and I am currently continuing my research in her lab.

Q. What led you to pursue research in neuroscience?

There’s a lyric in a song by AKMU that goes, “It’s amazing how people move,” and I think that perfectly captures why I became interested in brain research. Since I was young, I’ve always been curious about how I perceive the world, how I’m able to feel and move, and especially where the process of “thinking”—which happens constantly in my head—actually begins. That curiosity stayed with me for a long time, and eventually, I joined a sensory processing lab that studies the brain’s initial mechanisms for perceiving the world. That’s when my journey into neuroscience truly began.

Q. Could you introduce the Center for Synaptic Brain Dysfunctions?

The Center for Synaptic Brain Dysfunctions conducts brain science research aimed at understanding how the brain works, identifying the causes of brain disorders such as autism, and ultimately proposing potential treatment strategies.

Our research begins by analyzing behavioral patterns in laboratory mice under various conditions and investigating the brain mechanisms that drive those behaviors. We then use disease model mice—genetically and behaviorally similar to human patients with brain disorders—to examine what kinds of changes lead to abnormal behaviors. This analysis is done both at the level of individual synapses between neurons and in terms of interactions between different brain regions. Finally, we work to identify and propose treatment methods that could restore the brains of these model mice to a normal state.

Q. In March, a study demonstrated that sensory information processing in the brain is modulated by behavioral state. Could you briefly explain the research?

When we’re running, it’s often harder to hear sounds from our earphones or the surrounding environment. This happens because the brain prioritizes certain sensory inputs depending on which information is more important at the moment. In our recent study, we found that the brain changes the priority of visual and auditory information based on the animal’s behavioral state—whether it is stationary or running. In our behavioral experiments, we presented visual and auditory stimuli simultaneously to mice. We found that when the mice were stationary, they prioritized auditory information. However, when they were running, they prioritized visual information and made behavioral decisions accordingly.

Furthermore, we identified the neural mechanism behind this shift. In a region of the cerebral cortex called the posterior parietal cortex—which integrates visual and auditory signals—we discovered that motor signals generated in the motor cortex during running are transmitted to the auditory cortex. This suppresses the auditory signals from being relayed to the posterior parietal cortex. Through this mechanism, the brain adjusts the priority of sensory information based on behavioral state, effectively filtering information to meet the immediate demands of the environment.

Q. What led you to begin this study?

In a previous study from our lab, we found that mice with their heads fixed and remaining still tended to exhibit auditory-dominant behavior—meaning they prioritized auditory information. However, since most animals adapt their strategies and behaviors based on context, we hypothesized that mice might also prioritize visual information under certain conditions. Around that time, several studies began to report that the way neurons in the visual and auditory cortices respond to external stimuli changes when mice are running. Based on those findings, we asked a new question: "Could an animal’s movement state not only alter responsiveness in the sensory cortices, but also affect the entire audiovisual integration process—ultimately shifting the priority of sensory information?" This question became the foundation for launching this research project.

Q. Were there any particularly difficult moments or memorable episodes during your research?

Honestly, I don’t think there was a single moment in the research process that felt “easy.” One memory that stands out is from when I first started calcium imaging experiments. I spent two weeks performing surgeries on 20 mice, working day and night. But in the end, not a single neuron appeared in the imaging results. I still vividly remember the sense of futility I felt while editing those pitch-black images.

There were also holidays—like Lunar New Year and Chuseok—when I had to walk through a deserted campus to get to the lab for experiments. It felt like I was a character in a post-apocalyptic movie. I also recall the weeks spent revising analysis methods and figures over and over, only to realize in the end that the original version was the best. That moment of futility, too, has stuck with me. But ironically, it’s those tough experiences that made the successful data moments feel even more rewarding. The satisfaction of producing meaningful results through trial and error—that’s what keeps me going in this field.

Q. What research are you currently working on?

Right now, I’m studying how visual and auditory stimuli are integrated in the brain of healthy mice and how this leads to final behavioral decisions. To understand how external stimuli are perceived, we train mice to perform specific actions in response to either a visual or auditory stimulus in exchange for a reward. Once trained, the mice are presented with audiovisual stimuli that either match or conflict in meaning. We then observe their behavior while also recording and manipulating neural activity to investigate how audiovisual integration occurs in the brain.

In a previous project, we examined how the state of movement (whether the mouse was still or running) affected the audiovisual integration process. The current focus is on how the neural networks responsible for audiovisual integration change as the mice learn the meaning of the external stimuli. I’m involved in all stages of the research—from designing experiments and running behavioral tests to measuring and modulating neuronal activity and analyzing the resulting data.

Q. How would you explain brain research and its importance to the general public?

The brain is an incredibly important organ—it allows us to perceive the world, control our bodies, learn, remember, and feel emotions. Brain research is the scientific effort to understand how the brain works and how we think, feel, and behave. Yet, there’s still so much we don’t know about the brain, and many people around the world suffer from brain-related disorders. By studying the brain, we can better understand the causes of conditions like dementia, depression, and Parkinson’s disease, and ultimately develop more effective treatments. Moreover, cutting-edge technologies such as artificial intelligence (AI) and brain–machine interfaces (BMI) are often inspired by discoveries in brain science. This makes neuroscience not only essential for medicine but also a field with far-reaching impacts across many areas of science and technology.

Q. What technologies or trends do you think will be important in the future of brain research?

The field of neuroscience has been advancing at an incredible pace. New technologies now allow us to simultaneously measure the activity of thousands to tens of thousands of neurons and to manipulate neural activity with unprecedented precision. Thanks to these breakthroughs, we’re gaining a much deeper understanding of how the brain works.

Whereas past research often focused on specific brain regions, recent studies increasingly explore how different brain areas interact and work together. At the same time, new tools and methods are being developed to analyze large-scale, high-dimensional data quickly and intuitively. It really feels like we’re in the midst of the most revolutionary era for neuroscience.

I hope that these technological advances will one day allow us to record and interpret the activity of all tens of billions of neurons in a single brain.

Q. Lastly, is there anything you’d like to say?

I’d like to express my heartfelt gratitude to our Associate Director LEE Seung-Hee, who has always guided me throughout my journey. I’m also deeply thankful to my family for their unwavering support, to my lab colleagues who share in the experiments and challenges, and to everyone at IBS who provides tremendous support. I sincerely hope to continue making exciting and meaningful discoveries in the future.