Is the brain an emergent physical system?
Neurotechnology Center, Kavli Institute of Brain Circuits, Columbia University, USA
In physical systems built with many components, emergent properties, such as ferromagnetism, are often generated from the interactions among these units. These emergent properties are, by definition, invisible when observing individual particles, since they depend on large-scale interactions between them. Likewise, the function of the brain has been mostly studied by examining the responses of individual neurons, yet it is probably an emergent property that arises from the coordinated activity of large numbers of neurons in its neural circuits. To capture this emergent level of brain function, we, and others, have developed novel methods to measure and control neural activity across complete neural circuits in experimental animals and human patients. This technological effort, sponsored by the White House as its flagship BRAIN Initiative, is an interdisciplinary project that incorporates into neuroscience many methods and approaches from the physical sciences and nanotechnologies. Data obtained with these new methods could prove to be an invaluable step towards understanding neural computations and pathological brain processes.
In my talk, I will provide examples of how two-photon imaging of the activity of the visual cortex of awake behaving mice reveal indeed the existence of emergent functional states, as neurons are activated together in response to a visual stimulus. These coactive neuronal ensembles resemble the attractors of Hopfield's model of recurrent neural networks, based on the Ising model. Moreover, using two-photon optogenetics, we activate these ensembles and can change the behavior of the animals. Our results are consistent with the hypothesis that these dynamical attractors are the physical implementation of perceptual states or memories.
Rafael Yuste is a neurobiologist who invented the calcium imaging technique and other methods to measure and monitor neural activity in slices and in vivo. In his research he studies neural networks (rather than just single neurons) to understand the functioning of the brain. He is also one of the initiators of the White House BRAIN Initiative announced in 2013.
Yuste studied medicine at the Universidad Autónoma de Madrid and obtained his PhD at Rockefeller University in New York and worked as a postdoc in a biophysics group at Bell Laboratories. He became assistant professor in the Department of Biological Sciences at Columbia University in 1996, obtaining tenure in 2002 and becoming full professor in 2006. Since 2005 he is also co-director of the Kavli Institute for Brain Science at Columbia University. For his research he has received many awards, including numerous young investigator awards (1996-2002), the NIH Director's Pioneer Award (2013) and the Premio Lección Conmemorativa Jiménez Díaz (2015).