Nature’s Journal Club column is usually a good & always a short read providing exciting angles on scientific topics/papers from good researchers. Recently ‘neuroscientist’ Dave Featherstone argued for a broader approach to brain mapping by not restricting it only to the connectome between neurons. Neurons are making up less than 10% of the human brain while most brains cells are glia neglected by scientists making the wiring diagram of a ‘complete’ human brain.
For example, consider the recent study of adenosine and sleep led by Philip Haydon and Marcos Frank at the University of Pennsylvania in Philadelphia (M. M. Halassa et al. Neuron 61, 213–219; 2009). Adenosine binds to receptors on neurons, thereby regulating neuronal signalling. Interestingly, adenosine seems to represent ‘sleepiness': it accumulates during wakefulness and dissipates during sleep. Where does it come from? It is generated from adenosine triphosphate (ATP), which is secreted by astrocytes — a major type of glia.
Therefore, if we want to map the functional brain connections controlling sleep, we need to include glia and the extracellular space between glia and neurons. If we’re going to understand brain function by mapping the brain, we need to include most of the brain in our map.
I tried to draw an analogy between the situation in brain mapping and personal genomics on FriendFeed:
Update: it seems Dave Featherstone had something similar in mind as an analogy, he answered my email the following way:
Yeah, that’s a good analogy. The original version of my column said the connectome would be like if the human genome had only sequenced exons. But that sentence was cut for space considerations.