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burst activities is related to the nonlinear dynamical properties of neuronal
membrane and to the time-dependent coupling between neurons. On the other
hand, in order to obtain scale-free statistics of synchronized bursting events
timing, the background current has to be rendered with temporal correlation. It
was further suggested in Volman
et al
. (2004) that such currents can, at least in
part, represent the signaling from the network of glial cells that surrounds the
neurons.
12.6. Highly-Active Neurons
In contrast to the ongoing amplification in the activity of individual neurons
during network development, no dramatic changes are observed in their
synchronization to the network. By synchronization we mean the tendency of a
neuron to fire spikes solely during a SBE, where a non-synchronized neuron will
fire spikes during the network silence periods (between SBEs) as well (See
definition and measure of synchronization in Shein
et al
., in press). In Fig. 12.5A
we show a network activity, where most neurons are synchronized with the
network SBEs, while two neurons, marked by a "*" symbol on the left axis, are
unsynchronized. In Shein
et al
. (in press) we name these neurons as highly-active
(HA) neurons.
Most neurons are synchronized to the network from the onset of their activity.
They do not generate spikes endogenously, and their activity is always network-
dependent. In this sense, the synchronized firing is an innate property of most
neurons in the network. Despite the above, a small subset of HA neurons exhibit
an unsynchronized activity pattern between SBEs, in addition to firing during
SBEs. In Shein
et al.
(in press) it was shown that these neurons were the first
active neurons in the network during development, and that as synchronized
activity emerged, they were precursors of SBEs. This is also shown in
Fig. 12.5B, where a higher temporal resolution on one SBE shows that the two
HA neurons identified in Fig. 12.5A initiate spike-trains before the rest of
the neurons. Statistics over 3 different cultures is shown in Fig. 12.5C show
consistency. It was suggested that the HA neurons are involved in the regulation
of activity in the network (Volman
et al.
2004; Shein
et al.,
in press).
12.7. Function—Form Relations in Cultured Networks
Closer inspections of the SBEs, such as the one shown in Fig. 12.3, reveal that
each network burst could be described as a momentary spatio-temporal image in
