Understanding How Brief Stimuli Can Lead to Lasting Emotions in Humans and Mice

Emotions play a crucial role in guiding our decisions and actions, yet their underlying neural mechanisms remain only partially understood. Neuroscientists and psychiatrists have long struggled to decipher how brief sensory experiences can produce persistent emotional states, and how these processes may contribute to mental health disorders.

A recent groundbreaking study published in Science by Stanford Medicine researchers has shed light on this complex phenomenon. The team mapped brainwide neural activity related to emotional responses triggered by mildly unpleasant sensory stimuli, revealing that both humans and mice share similar neuronal processing patterns. This evolutionary conservation suggests that fundamental principles govern emotional responses across mammals.

The researchers focused on responses to safe, reproducible stimuli—using a device common in eye examinations that delivers controlled puffs of air to the eye. These air puffs, deemed unpleasant but not painful, allowed precise timing and measurement of neural responses. Participants reported feeling annoyed or uncomfortable, and this negative state persisted beyond the stimulus, indicating emotional engagement.

By recording brain activity in patients with implanted electrodes and in mice exposed to the same stimuli, the team observed a two-phase neural response: a rapid initial activation followed by a sustained second phase associated with emotional processing. Remarkably, the same patterns appeared across species, underscoring an evolutionarily conserved mechanism.

To probe the significance of this sustained activity, the team administered ketamine—a drug known for its anesthetic and antidepressant properties. They found that ketamine shortened the duration of the second phase of brain activity, effectively dampening the emotional response without affecting the initial reflex. This effect was consistent in both humans and mice, highlighting the second phase’s role in emotional persistence.

These findings suggest that timing and duration of certain brain activity patterns are crucial in the formation and maintenance of emotional states. Disruptions, whether too prolonged or too brief, may contribute to neuropsychiatric disorders like schizophrenia, depression, or PTSD. Understanding these timing dynamics opens new pathways for targeted treatments, potentially involving modulation of neural activity patterns.

The study also emphasizes that these principles could be fundamental to understanding how the brain integrates sensory information to produce lasting emotional memories and states, informing future research and therapy development to improve mental health outcomes.