Synaptic pruning

File:SynapseIllustration.png

A typical view of the synapse. In babies and newborn children, these can be completely pruned from the structure as they become too large or expansive, and be modified or replaced by more efficient configurations.

In neuroscience, synaptic pruning, neuron pruning or neuro-structural re-assembly is a neurological regulatory process, which facilitates a productive change in neural structure by reducing the overall number of overproduced or "weak" neurons into more efficient synaptic configurations. It is often a synonym used to describe the maturation of behavior and cognitive intelligence in children by "weeding out" the weaker synapses.

Introduction

Regulatory and regenerative purpose

The purpose of synaptic pruning is a simple means of removing un-necessary neuronal structures from the brain; as the human develops, the need to understand more complex structures becomes much more pertinent and more simple associations formed at childhood are thought to be removed for more complex structures.

Despite the fact it has several connotations with regulation of cognitive childhood development, pruning is thought to be a process of removing neurons which may have become damaged or degraded in order to further improve the "networking" capacity of a particular area of the brain. Furthermore, it has been stipulated that the mechanism not only works in regards to development and reparation, but also as a means of continually maintaining more efficient brain function by removing neurons by their synaptic efficiency.

During maturation phases in humans

In terms of humans, synaptic pruning has been observed through the inference of differences in the estimated numbers of glial cells and neurons between children and adults, which differs greatly in the area of the mediodorsal thalamus.

In a study conducted in 2007 by Oxford University, it was found that by comparing 8 newborn human brains with those of 8 adult brains using estimates based upon size and gathering from stereological fractionation, showed that on average, adult neuron estimates were 41% lower than those of the newborn.

However, in terms of glial cells, adults had far larger estimates than those in newborns; 36.3 million on average in adult brains, compared to 10.6 million in the newborn samples. In terms of the development of the brain, the structure is thought to change due to the structural changes, in which degeneration and deafferentation occur in postnatal situations, although in terms of some studies, these phenomenon have not been observed. In the case of development, neurons which are in the process of loss via programmed cell death are unlikely to be re-used, but rather replaced by new neuronal structures or synaptic structures, and have been found to occur alongside the structural change in the sub-cortical gray matter.

References

1. Abitz, Damgaard et al. (2007) Excess of neurons in the human newborn mediodorsal thalamus compared with that of the adult, Oxford, Oxford Journals [1] (Licensed under a Creative commons license)
2. Chechik, Gal & Meilijison, Isaac. (1999). Neuronal Regulation: a mechanism for synaptic pruning during brain maturation Israel:Stanford Journals [2] (No license specified)