A well-studied and understood example of a neural word is the spatio-temporal pattern of neuronal activity in the antennal lobe (AL) of insects in response to odor stimuli (Figure 3A–C; Laurent 2002; Laurent et al., 2001; MacLeod and Laurent, 1996). When an odor is presented, it induces a transient gamma frequency oscillation in the AL neuronal population, with different small subsets of AL neurons firing in each oscillation cycle. The odor is thus represented (or ‘coded’) by an evolving sequence of activity vectors (a neural word or trajectory), lasting for a few hundred milliseconds. Successive presentations of the same stimuli evoke similar trajectories (Figure 3A, inset), whereas different odors are associated with uniquely different sequences of projection neurons (Broome et al., 2006; Mazor and Laurent, 2005).
