We apply the Triple Correlation Uniqueness (TCU) theorem to the most basic representation of network spiking activity, the raster, to prove that third-order (triple) correlation uniquely characterizes spiking activity in the brain. As a consequence, the three-node (triple) motifs comprising the triple correlation are fundamental building blocks of neuronal activity. By analysing the putative flow of information in these motifs, we group all possible motifs into fourteen motif-classes. These motif-classes embody well-known and well-studied properties in neuroscience, e.g. spike rate, local dynamics, synchrony, feedback, feedforward, convergence, and divergence. We show that motifs with some of these properties---divergence, convergence, and feedforward---are far more prevalent in the triple correlation; and thus, these properties contribute more to characterizing neural activity than do the other properties. In the frequency domain, the triple correlation is the bispectrum, which characterizes the phase-relationship between spike trains and the relationships between frequency bands. We apply these analyses to example rasters to illustrate the dependence of our characterization on the firing patterns underlying neural activity.