Connectivity in Living Neural Networks. Can we build a brain?

Naturally formed nervous systems such as a brain are extremely complex, and
their precisely wired connectivity appears to be behind their rich activity
repertoire and astonishing computational capabilities. However, the same
neurons dissociated and cultured on glass coverslips show simple activity
patterns characterized by the synchronous \"all-or-none\" firing of the
network\'s population. To uncover the secrets of neuronal connectivity and
its role in governing activity, I have been working for the last five years
in new experimental platforms to describe connectivity in living neuronal
networks. In the first part of the talk I will introduce a graph-theoretical
approach that, combined with measurements on neural activity, provides
relevant statistical information of the neural connectivity. Among other
quantities, we can assess the average connectivity of the network or the
distribution of connections. The latter appears to be Gaussian in
two-dimensional neuronal cultures, very different from the small-world or
power law distributions present in natural nervous systems. In the second
part of the talk I will introduce new experimental strategies currently
under development in my group. These strategies are focused on the
confinement of neurons and connections in predefined patterns to control the
network\'s circuitry. These \"engineered neural networks\" appear to have a
much more complex connectivity and richer activity patterns than standard
cultures, and are excellent model systems for the advancement of
network-theory concepts and neuronal computation.