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seizures in both human and animal experiments (Yang
et al.
2003). This cooling
of the brain might have reduced the neuronal activity while leaving the general
connectivity intact, as seen in our model.
All of the above findings describe our cultured neuronal network as a
complex dynamical biophysical system that has some forms of intrinsic memory,
information coding and self-regulation. By applying different forms of
manipulations, such as morphology constrains and thermal stimulations, we
discovered repeating activity motifs and observed the network's long term
adaptation to a changing environment. These kinds of network characteristics fit
well to the notion that the brain is composed of such complex living network
systems.
Future experiments on cultured networks may continue to reveal higher levels
of network plasticity and communication forms. For example, we already
mentioned our recent work (Baruchi and Ben-Jacob, 2007) in which we have
shown that new "memories" may be imprinted into a given neuronal network. By
carefully placing microscopic droplets of chemicals, new regions in the network
could be activated to consistently generate new SBE motifs. An interesting
continuation to this research will be to determine the maximal number of SBE
motifs that may be imprinted into a given network, and how are they related to
the network morphology, topology and excitation state.
The observed SBE motifs in our cultures suggest that a random ensemble of
neuron cells will not produce a random "jumble-mumble" of signals, but are
rather forced into a small number of repeating patterns or attractors. Though the
SBE motifs shown in our cultures are not necessarily associated with real brain
"memories", they can still hint that the brain may work in specific highly
regulated patterns, in which memories are pulled out and stored in controlled
processes.
Acknowledgments
We are thankful to Inna Brains for her devoted technical assistance in extraction
of the cells and the networks plating and monitoring. This research has been
supported in part by the Tauber Foundation and te Maguy-Glass chair in Physics
of Complex Systems at Tel Aviv University. Vladislav Volman acknowledges
the support of the U.S. National Science Foundation I2CAM International
Materials Institute, grant DMR-0645461.
