Human brains contain billions of nerve cells, or neurons. There are huge variations in the structure and form of these neurons, and even vast differences in properties within the same structural groups.
Now, scientists have shown for the first time that these differences are influenced by local connections within information hubs in the brain, as well as by the different kinds of sensory information the hubs receive.
Troy Margrie of the MRC's National Institute for Medical Research (NIMR; now part of the Francis Crick Institute) explained: "Imagine the cultural and sub-cultural differences of everyone living in London. Mix them up and randomly position them across a map of London. These people represent the neurons in a mammalian brain.
"Now imagine London as a city where the only information coming in is via the tube lines - with no television, radio, internet or phones. The Northern line information (for example, smells) is not only very different to the District line information (such as sounds) but each stop on the Northern line processes different kinds of smells. The people who belong to the same information hub - that is, live around the same tube stop - and receive their own unique type of information, are far more similar to each other than to those living at other tube stops and receiving other kinds of information."
The variations in structure and form - or biophysical properties - of different neurons affect the tasks they carry out. For instance, one such biophysical property, called sag potential, influences the input and output functions of most neurons. In this study the scientists looked at variability in sag potential in a part of the brain responsible for processing smells - the olfactory bulb - where functionally distinct networks of neurons can be identified.
They found that differences in sag potential across these networks were not random but were associated with functionally discrete local circuits. Their findings indicated that interactions among neurons belonging to the same sensory circuit influenced their biophysical properties. And cells processing the same kind of information were more similar than neurons processing different information.
Dr Margrie said: "This work describes a fundamental organising principle that underlies biophysical variations in the neurons and connections in our brains. This new data informs us of the basic function and adaptive qualities of such circuits that is required to understand the operation of healthy and diseased brains."
The research was carried out by Dr Margrie's team at University College London and NIMR. The paper,' A biophysical signature of network affiliation and sensory processing in mitral cells' is published in Nature.
