Brain Architecture Pruning Discovery Challenges Tabula Rasa Theory of Infant Memory Formation and Spatial Navigation

ISTA researchers find that hippocampal networks start dense and "full," pruning connections over time to optimize memory formation and spatial navigation.

By: AXL Media

Published: Apr 27, 2026, 5:58 AM EDT

Source: Information for this report was sourced from EurekAlert!

The Biological Reality of the Full Slate

The philosophical debate between a blank slate and a pre-set blueprint has found a new biological answer within the hippocampus. Research led by Prof Peter Jonas at the Institute of Science and Technology Austria (ISTA) suggests that memory formation does not begin on a "tabula rasa." Instead, the neural networks responsible for spatial orientation and long-term memory transition from a state of "tabula plena," or a full slate. This indicates that the brain is born with an abundance of connections that provide a foundational structure, rather than starting with a void that must be filled entirely by environmental experience.

Mapping the CA3 Network Over Time

The study utilized mouse brains to track the evolution of interconnected CA3 pyramidal neurons across three distinct life stages: early postnatal, adolescence, and adulthood. Using the patch-clamp technique, ISTA researcher Victor Vargas-Barroso measured electrical signals at presynaptic terminals and dendrites to map how these networks communicate. The findings revealed that in the days immediately following birth, the hippocampal network is characterized by a high density of connections that appear to be organized randomly. This dense initial phase serves as the starting point for all subsequent cognitive development and memory integration.

The Paradox of Developmental Pruning

Contrary to the intuitive assumption that a brain network would grow denser as an organism learns, the researchers observed a streamlining process. As the subjects matured from adolescence into adulthood, the hippocampal configuration became sparser and more refined. Prof Jonas described this as a "pruning model," where the brain starts with an exuberant amount of connectivity and then systematically optimizes it. This optimization process involves strengthening essential links while removing redundant or less efficient ones, resulting in a more structured and functional neural architecture in the adult brain.