A research team from the Institute for Neurosciences (IN), a joint center of the Spanish National Research Council (CSIC) and Miguel Hernández University of Elche (UMH), has mapped how the cerebellum forms connections with other parts of the brain during early development. Their findings, published in Proceedings of the National Academy of Sciences (PNAS), detail how these neural pathways emerge, grow, and become refined over time, providing a comprehensive map of cerebellar projections in the developing mouse brain.
Traditionally linked to motor control, recent studies indicate that the cerebellum is also involved in emotional regulation, social behavior, and cognitive functions. The timing and process by which it begins communicating with other brain regions were previously unclear. This uncertainty led the Development, Wiring and Function of Cerebellar Circuits group at IN, headed by Juan Antonio Moreno Bravo, to investigate further.
The researchers found that connections between the cerebellum and other areas start forming very early in embryonic development. "We observed that cerebellar projections begin to form very early, already in the embryo, when the first axons start connecting with their target regions," said Moreno Bravo. These pathways then rapidly expand as the brain undergoes significant growth during initial stages.
During postnatal weeks, these circuits go through a refinement period where permanent connections are established. "This stepwise sequence allowed us to pinpoint the periods when the cerebellum may start influencing other brain regions, even while it is still in an immature developmental stage. These early periods represent highly relevant windows for understanding how the brain establishes its internal architecture," Moreno Bravo added.
The study used advanced genetic tools and three-dimensional imaging techniques. Researchers labeled specific neurons within deep cerebellar nuclei using fluorescent markers and employed tissue-clearing and microscopy methods to visualize axon paths throughout the brain.
"Seeing these projections in 3D, how they emerge in the embryo and spread throughout the brain, was truly fascinating," said Raquel Murcia Ramón, first author of the study. "Many of these connections had never been seen with such precision, and being able to observe their evolution in time allowed us to reconstruct a full developmental story of these circuits," she added.
The results suggest that the cerebellum may play an earlier role in shaping neural networks than previously assumed. "It has traditionally been assumed that the cerebellum matures late and that its involvement in complex functions emerges gradually and only at later stages. Our work suggests the opposite: the cerebellum begins building its network very early and may already be actively contributing to the formation of circuits in other brain regions from initial developmental phases," explained Moreno Bravo. He noted this perspective could prompt a reevaluation of how scientists view cerebellar contributions during development.
The mapping created by IN CSIC-UMH provides a reference point for future studies on cerebellar connectivity from birth onward. It also offers a timeline for examining how genetics or environmental factors might impact this process or lead to neurodevelopmental disorders. "This work lays the groundwork for exploring not only how the cerebellum contributes to typical brain development, but also how cerebellar alterations could give rise to pathological conditions, including some linked to neurodevelopmental disorders," researchers stated.
Funding for this study came from several sources: The European Research Council under Horizon 2020; Spain's State Research Agency – Ministry of Science, Innovation and Universities; and support from Spain’s Severo Ochoa Program for Centers of Excellence.
