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Fig. 12.5. Highly-active neurons in culture. (A) Network activity showing SBEs. Two HA neurons
are identified by "*" symbols on the left axis. These neurons fire a substantial percentage of their
activity between SBEs. See Ref. Shein
et al.
(2008) for specific details and measures of HA
neurons. (B) A closer view of one SBE showing that the same two neurons from (A) are precursors
to the rest of the neurons and are the first to initiate their spike-train firing. (C) Statistics over 3
different cultures show that in most cases, the first neurons to fire during a SBE are HA type.
Figure taken with permission from Shein
et al
., in press.
which neurons at different locations fire spike-trains at different delays relative to
each other. A single culture will usually show a few different SBEs, each with its
own characteristic pattern of neuronal firing time ordering (activity propagation)
and neuron temporal correlations. Nevertheless, in many of the cultures it is
possible to detect SBEs that share a similar propagation profile between the
recording sites, i.e. a repeating motif. For example, Fig. 12.6 shows four different
spatio-temporal patterns of SBE propagation in one single culture. This culture
was divided into four sub-networks connected in a ring-like shape. The figure
clearly shows that the activity in each mode of SBE begins in one region,
propagates to the neighboring regions and ends in the region at the opposite side
of the initiation cluster. Each image in Fig. 12.6 is composed from several tens of
SBEs, showing a clear repetition of the pattern for each mode.
Several works suggested explanations for the burst repetition in propagation
profile, such as network morphology of substructures of cell clusters (Gross and
Kowalski, 1999), existence of endogenously active neurons (Latham
et al
.,
