Instead, methodological constraints lead to a natural division of labor (and enthusiasm) across three complementary domains of the connectome landscape: the micro-, meso-, and macroconnectomes (Akil et al., 2011). Each domain aims to map connectivity down to the spatial resolution of the available methodologies and over as large a spatial expanse as is technically feasible. Every brain is an extremely complex network. Two fundamental and complementary levels of description
are those of maps and connections. Maps refer to the spatial arrangement of brain parts (parcels), along with countless LY2157299 types of information that can be associated with each spatial location or each parcel. This is the domain of brain cartography—how maps are generated, visualized, and navigated, and what information can be represented on them. Connections are, in essence, pairwise relationships indicating the existence, strength, and/or polarity of links between different locations or different parcels as determined directly using anatomical methods or as inferred using one or another indirect imaging method. When the analysis p38 MAPK inhibitor aims to be comprehensive rather than piecemeal, connectivity studies fall into the realm of connectomics. Why is connectomics important? Skeptics can correctly point out that
knowing a complete wiring diagram will not on its own tell us how the brain works. For example, the availability of a complete nematode connectome
(White et al., 1986 and Varshney et al., 2011) leaves open many mysteries of how its nervous system actually processes information—i.e., how it “computes.” A starting counterpoint is to invoke the analogy of the genome: knowing the precise sequence of three billion base pairs in the human genome on its own tells us precious little about how our bodies and brains are assembled and regulated by genes and regulatory sequences. Yet the early skeptics of the Human Genome Resminostat Project have largely been quieted by the awesome success of modern genomics—even though it remains humbling to realize how much is not yet understood about the workings of the genome. However, the reasons for mapping connectomes arguably goes deeper, because the precise wiring of the brain is fundamental in constraining what it can (and cannot!) compute. The brain is not a general-purpose computer that can support a variety of operating systems and software applications. Instead, the software (functions) and hardware (the squishy stuff) are intimately coembedded with one another. This Perspective focuses on brain cartography and connectomics in three intensively studied species: human, macaque monkey, and mouse. The emphasis is on cerebral cortex, owing to its physical dominance as well as the special challenges it poses, but subcortical and cerebellar domains are considered as well.