After a short period of growth, cultured networks of neurons regularly exhibit major activity in the absence of external stimulation. These "bursts" are entirely related to growth. At this stage, they have little to do with learning behaviour, as the network is still too young to sustain a process of memory formation. This has now for the first time been simulated for networks ranging in size from 10,000 to 50,000 neurons. The simulations provide insight into the role of the growth process in initial activity. Researchers at the University of Twente's MIRA Institute recently published details of this work in PLOS ONE.
"Isolated" neurons, which have yet to form any interconnections, soon put out cell extensions (axons and dendrites) that connect them to other neurons. The resultant network starts to show signs of activity after just one week. The researchers made these observations in networks that they had cultured from neurons extracted from the brains of young rats. These cells were grown in culture dishes whose bases had been fitted with electrodes. Here, the network grows in a single plane, as far as possible. If it were to grow "upwards" (3D), it would be difficult to determine what was actually being measured. After a week, observations show that the neurons have become active and that they start to "fire". This activity can be seen to pass through the entire network in the form of a "burst".