Scientists trace the arrow of time to interactions between neurons

Key Points:

• Researchers developed an information-theoretic method to decompose a system’s local arrow of time into contributions from individual components, pairs, triplets, and larger groups, revealing how irreversibility emerges from microscopic interactions.
• Applying this method to recordings from 53 salamander retinal neurons showed that pairwise interactions accounted for 66% to 74% of local irreversibility, indicating that neural irreversibility largely arises from relationships between neuron pairs.
• Surprisingly, the retinal activity exhibited a stronger arrow of time when viewing a statistically time-reversible Brownian-motion stimulus than when viewing a natural movie, demonstrating that neural irreversibility is not simply a reflection of external temporal asymmetry.
• The study’s framework provides a quantitative approach to understanding how the arrow of time emerges in complex biological systems and could be applied beyond neuroscience to other nonequilibrium systems with many interacting components.
• These findings highlight that large-scale temporal directionality in complex systems can often be traced back to surprisingly simple pairwise interactions, offering new insights into the microscopic origins of time’s arrow.