Unlike in written language syntax, where contiguous series of fundamentals (letters) constitute words and sentences, in neural syntax multiple words can overlap and generate both first order and higher order patterns, much like in music. Figure 6 illustrates the genesis and syntactic structure of such interleaved assemblies. The spiking patterns of hippocampal place cells can be approximated by a Gaussian spatial field, modulated by the theta frequency oscillation (Fig. 6A, C; Samsonovich and McNaughton, 1997). The Gaussian fields of different place cells, representing upcoming places or items, can overlap and their temporal relationships are governed by a ‘compression’ rule: within the theta cycle, the spike timing sequence of neurons predicts the upcoming sequence of locations in the path of the rat, with larger time lags representing proportionally larger distances (Fig. 6A, C; Dragoi and Buzsáki, 2006; Skaggs et al., 1996).12 The consequence of the time lags between the spikes of the transiently oscillating neurons is that the oscillation frequency of their population output, also reflected by the local LFP, is slower than the mean of the oscillating frequencies of the
