Cordis | Researchers believed neurons in the brain communicated through physical connections known as synapses. However, EU-funded neuroscientists have uncovered strong evidence that neurons also communicate with each other through weak electric fields, a finding that could help us understand how biophysics gives rise to cognition.The study, published in the journal Nature Neuroscience, was funded in part by the EUSYNAPSE ('From molecules to networks: understanding synaptic physiology and pathology in the brain through mouse models') project, which received EUR 8 million under the 'Life sciences, genomics and biotechnology for health' Thematic area of the EU's Sixth Framework Programme (FP6).
Lead author Dr Costas Anastassiou, a postdoctoral scholar at the Californian Institute of Technology (Caltech) in the US, and his colleagues explain how the brain is an intricate network of individual nerve cells, or neurons, that use electrical and chemical signals to communicate with one another.
Every time an electrical impulse races down the branch of a neuron, a tiny electric field surrounds that cell. A few neurons are like individuals talking to each other and having small conversations. But when they all fire together, it's like the roar of a crowd at a sports game.
That 'roar' is the summation of all the tiny electric fields created by organised neural activity in the brain. While it has long been recognised that the brain generates weak electrical fields in addition to the electrical activity of firing nerve cells, these fields were considered epiphenomenon - superfluous side effects.
Nothing was known about these weak fields because, in fact, they are usually too weak to measure at the level of individual neurons; their dimensions are measured in millionths of a metre (microns). Therefore, the researchers decided to determine whether these weak fields have any effect on neurons.
Experimentally, measuring such weak fields emanating from or affecting a small number of brain cells was no easy task. Extremely small electrodes were used in close proximity to a cluster of rat neurons to look for 'local field potentials', the electric fields generated by neuron activity. The result? They were successful in measuring fields as weak as one millivolt (one millionth of a volt).
Commenting on the results, Dr Anastassiou says: 'Because it had been so hard to position that many electrodes within such a small volume of brain tissue, the findings of our research are truly novel. Nobody had been able to attain this level of spatial and temporal resolution.'
What they found was surprising. 'We observed that fields as weak as one millivolt per millimetre robustly alter the firing of individual neurons, and increase the so-called "spike-field coherence" - the synchronicity with which neurons fire with relationship to the field,' he says.
