Cross-Species Study Reveals Unique Brain Responses to Eye Puffs

A recent study published in the journal *Science* demonstrates a novel cross-species approach to understanding emotional responses in both mice and humans, prompted by air puffs directed at the eye. This research, led by Dr. Karl Deisseroth, a professor of bioengineering and psychiatry at Stanford University, highlights the brain's complex responses to sensory stimuli, bridging a significant gap in emotion research across species.

The study, published on May 29, 2025, identifies distinct sensory and affective brain responses elicited by the eye puffs, which were found to be both unpleasant and irritating for participants. Both species exhibited reflexive blinking and prolonged eye closure, suggesting a shared experience of discomfort. The investigation utilized advanced brain recording techniques, including single-unit Neuropixels probes in mice and implanted electrodes in human subjects undergoing seizure monitoring, revealing intricate brain activity patterns that linger beyond the initial sensory response.

Dr. Deisseroth’s work is significant because it addresses a long-standing challenge in emotion research: the difficulty of studying subjective experiences in non-verbal subjects such as animals. According to Nicole Rust, a professor of psychology at the University of Pennsylvania, this innovative study provides a much-needed protocol for exploring emotional states systematically across different species.

Despite the promising findings, some experts remain cautious about categorizing the observed brain states as emotions. Ralph Adolphs, a professor of psychology and neuroscience at the California Institute of Technology, argues that while the study presents a valuable methodology for investigating emotions, it does not definitively prove that the brain state induced by eye puffs equates to an emotional experience. He emphasizes the need for additional experiments to strengthen the conclusions drawn from this research.

The study's design was inspired by a previous case in which Dr. Deisseroth's team observed brain activity in a patient who experienced a dissociative state prior to a seizure, leading to the hypothesis that similar dissociation could be induced in both mice and humans through the same stimulus. The eye puffs, chosen for their safety and comfort level, were shown to provoke significant changes in brain dynamics, particularly in higher-order brain areas associated with emotional processing.

Critics like Joseph E. LeDoux, a professor of neural science at New York University, argue that the nature of the stimulus used in the study may not adequately represent the complexities of human emotional experience. He contends that while the behavioral responses of the mice may mirror those of humans, it is challenging to assert that the subjective experience is comparable.

Meryl Malezieux, a postdoctoral researcher at the Max Planck Institute of Psychiatry, acknowledges that the study provides an elegant framework for future research but agrees with Adolphs that additional experiments are necessary to validate the emotional implications of the findings. She suggests that incorporating physiological measures, such as heart rate and respiration, could enhance the understanding of the emotional states observed during the experiment.

This cross-species protocol not only opens new avenues for emotion research but also raises critical questions about the fundamental nature of emotions themselves. As Dr. Adolphs notes, the discussions sparked by the study push the field forward by challenging researchers to define what constitutes an emotional state.

As neuroscience continues to unravel the complexities of the brain, this study exemplifies the potential for innovative methodologies to bridge the gap between animal and human research, paving the way for deeper insights into the emotional experiences that shape behavior across species.