Understanding How the Brain Detects Surprises and Its Implications for Mental Health

The human brain continuously predicts sensory information based on previous experiences and current movements. When actual sensory input diverges from these expectations—such as when a sound is delayed or distorted—certain neurons respond with a distinctive signal known as a prediction error. A recent study led by neuroscientists at the Friedrich Miescher Institute has shed light on how the brain detects and processes these moments of sensory mismatch.

Previous research demonstrated that in mice, visual mismatches—like a sudden pause in visual flow during running—trigger strong prediction error signals. Researchers wanted to explore whether similar mechanisms apply to other senses, like hearing. Magdalena Solyga, a postdoctoral researcher, designed experiments where mice ran through a corridor with sounds increasing in volume correlated to their movement. Occasionally, sounds would be muted, creating a mismatch between expectation and perception. Neurons in the auditory cortex responded strongly, revealing that prediction error signaling is not limited to vision but is a general feature of sensory processing.

Expanding this research, the team introduced simultaneous mismatches in visual and auditory stimuli, which resulted in a brain response more robust than the sum of individual mismatches. This indicates that the brain integrates multisensory prediction errors in a complex, nonlinear fashion.

Building on mouse studies, researchers adapted their experiments for humans by using EEG recordings and virtual reality headsets. Participants navigating virtual environments experienced sudden visual freezes while their bodies continued moving, eliciting clear mismatch responses similar to those in mice. These findings may pave the way for developing brain-based biomarkers for psychiatric conditions, such as psychosis, where abnormal responses could aid diagnosis or monitor treatment efficacy.

However, translating these findings into clinical practice faces challenges, including the technical difficulty of recording brain signals during movement, which introduces noise. The current studies involved 17 healthy adults, with plans to expand the sample size to bolster reliability. The research also raises important scientific questions about how prediction errors are processed across different brain areas and whether specific regions integrate multisensory mismatches.

This groundbreaking research is published in "eLife" and opens new avenues for understanding sensory processing and its relevance to mental health.