What kind of network is the brain?

The different areas of the cerebral cortex are linked by a network of white matter, comprising the myelinated axons of pyramidal cells. Is this network a neural net, in the sense that representations of the world are embodied in the structure of the net, its pattern of nodes, and connections? Or is it a communications network, where the same physical substrate carries different information from moment to moment? This question is part of the larger question of whether the brain is better modeled by connectionism or by symbolic artificial intelligence (AI), but we review it in the specific context of the psychophysics of stimulus comparison and the format and protocol of information transmission over the long-range tracts of the brain. Brain networks may be considered as neural nets in which the information is embodied in the structure of the net, or as communication networks in which the same physical substrate carries different information from moment to moment. Different types of network may be present at different levels.Psychophysical results and the remarkable sparsity of long-range white matter connections suggest that the central connectome of the brain may be a communications network. The format of the data transmitted via this network is one of the most important unsolved questions of neuroscience.If the white matter tracts do constitute a communications network, the network almost certainly requires analogs of the transmission control protocols (TCPs) used in man-made networks to control the flow of data and avoid overflow of buffers. A subset of axons within the tracts may carry the control signals.