The Physics of Neurons

Does the brain really operate like some kind of extra-complex computer, with logic gates and circuits made of the synapses that connect one neuron to another?

In 2009, we wrote:

In the future, the interface between brain and artificial system might be based on nerve cells grown for that purpose. In research that was recently featured on the cover of Nature Physics, Prof. Elisha Moses of the Physics of Complex Systems Department and his former research students Drs. Ofer Feinerman and Assaf Rotem have taken the first step in this direction by creating circuits and logic gates made of live nerves grown in the lab.

In his latest research, Moses, together with neurobiologist Prof. Menachem Segal and postdoctoral fellow Dr. Yaron Penn, suggests that the communication between neurons is less logic circuit and more “synergy.” Their experimental artificial nerve cell network has now grown to several hundred neurons – enough to begin observing interesting phenomena.

Neurons in a lab dish act synergistically

Moses, Segal and Penn were looking for a “leader” – a neuron that would set off a chain of electric pulses running through the network. Instead, they found that neurons are naturally “nervous,” oscillating constantly. When a signal needs to be formed, the individual oscillations became synchronized, neighbors adjusting their wavelengths to one another until a group of neurons emits a single, coordinated pulse. This is an emergent phenomenon, like fireflies flashing in harmony, and it needs no leader to make it happen.

Do the neurons in our brains really work this way? There is some evidence that they do. If so, it could be one of those small but fundamental shifts in understanding that changes the way that experiments are conducted, data analyzed, and artificial intelligence designed. Penn reports that they were able to turn the oscillations up or down – basically by controlling the calcium intake of the cells, which led to more or less connectivity and more or less excitability. Connecting these two parameters, say the scientists, suggests new leads into such disorders as epilepsy, which looks a lot like an imbalance between the two.

Oscillations of an individual neuron in a calcium-free medium. At left - 110 minutes, at right 100 seconds. On top -firing rate (spikes/200msec), at bottom -FFT spectrogram