An Internet network in our brain

The complex system is our brain is not organized in a hierarchy but more like a network like the Internet where everything communicates with everything. One way that would allow the brain to use alternative routes in case of neuronal damage.

Our brain is pretty well mapped: the left and right hemispheres and the different lobes, the cerebellum, the corpus callosum ... The functions of different regions were also well defined (areas of language, motor skills, vision ...). This is not a mystery, neurons are the basic building block of the brain. These cells with long axon extensions are essential for communication within the brain at the synapse, the region between two neurons, molecules are released by the axon and captured by the neuron to be activated.

But how is organized neural network is managed and how the flow of information permanent? Initially, scientists opted for a more hierarchical network where one or more neurons pass information to the neurons following on a clear chain. With one hundred billion neurons in the human brain, the organization must indeed be perfect! Yet, the workings of neural networks are still a mystery.

The phenomenal amount of work and especially the lack of tools were the brakes to the study of international relations neurons. However, the National Institute of Health has announced its intention to map all human neural networks, called connectome, with funding from the Human Connectome Project. The tools of neuroscience have indeed changed and now seem powerful enough to do so.

Sample images of the same region obtained through the simultaneous use of two tracers specifically recognized by two different antibodies. PNAS

Alternative networks Relief

Scientists at the University of Southern California (USC) have developed a technique derived from existing brain imaging techniques, but more powerful because it is now possible to simultaneously view four neuronal tracers. The method involves injecting two tracers into two pairs of sites in rat brain: each pair of markers comprises a molecule anterograde (which crosses the synapse to the neuron) and a retrograde molecule (which goes along the axon).

The collection of brains of rats, achieving cuts and observation by confocal microscopy to visualize the tracers after the addition of fluorescent antibodies specific to each (one color is assigned to each tracer) and thus determine the neurons involved in circuits. This technique allows viewing two channels or areas of the same circuit simultaneously in both directions.

The researchers have applied this method to a region of the rat brain involved in the satisfaction you get from the food and have their comments published in the journal PNAS. The results show a very complex circuit in the form of loops and circuits that do not seem to hierarchical: there is neither up nor down, just like the Internet.

While that indicated by this work, this hypothetical model of neuronal connections has not been proven. Neural circuits must be observed physiologically validated for their biological reality and functional. However, the roles of neurons might confer an advantage: a schism between two neurons leave the circuit remains in operation through the existence of alternative connections. This strategy protects the brain against brain damage, that the assumption of hierarchical connections does not.