Neurons in brain's memory region mature from dense, random links to structured, refined ones: Study

Neuron networks in the brains hippocampus, the memory centre, are dense with connections that appear random, but as animals mature, the networks become sparser but more structured and refined, a study has found.

Neuron networks in the brain's hippocampus, the memory centre, are dense with connections that appear random, but as animals mature, the networks become sparser but more structured and refined, a study has found. ''Intuitively, one might expect that a network grows and becomes denser over time. Here, we see the opposite. It follows what we call a pruning model: it starts out full, and then it becomes streamlined and optimised,'' lead researcher Peter Jonas, from the Institute of Science and Technology Austria (ISTA), said. Hippocampus is a key brain region involved in forming memories and guiding spatial navigation. It converts short-term memories into long-term ones, helping one retain and build upon experiences. The study, published in the journal Nature Communications, looked at how the central neural network in the hippocampus develops after birth. At the heart of the philosophical concept, whether new information is written on a ''blank slate'' or a ''full slate'', lies a fundamental question of ''Is everything pre-set from the very beginning or do experiences shape who we become?'' the researchers said. They added that biology too reflects the controversy -- between genes that provide the basic blueprint and environmental factors that sculpt the final organism. The central network in the hippocampus is made up of interconnected 'CA3' pyramidal neurons, which store and recall memories through a process known as plasticity -- it refers to the ability of neurons to constantly change, by strengthening or weakening connections or by reshaping structure. Brains of mice at three developmental stages were examined -- early after birth (day 7-8), adolescence (day 18-25), and adulthood (day 45-50). The researchers analysed the central neural network in the hippocampus by applying the 'patch-clamp technique' to measure tiny electrical signals in specific parts of neurons, such as at the signal-sending ends (presynaptic terminals) or branching sites that receive signals (dendrites). Advanced microscopy and laser-based methods were also used to observe processes inside the neurons and activate individual connections with high precision. The authors showed that ''the hippocampal CA3 network undergoes a developmental transformation from local, dense, and random connectivity to a distributed, sparse, and structured configuration.'' ''Thus, sparse and structured connectivity may emerge via experience-dependent mechanisms,'' they said.