Neuronal transients.

A recent letter to Nature (Vaadia et al. Nature, Lond. 373, 515-518 (1995)) presented compelling results concerning neuronal interactions in monkey cortex. Vaadia et al. made two fundamental points: (i) it is possible that cortical function is mediated by dynamic modulation of coherent firing among neurons; and (ii) these time-dependent changes in correlations can emerge without modulation of firing rates. These observations have severe implications for models of neural coding and empirical approaches that are based on firing rates (e.g. neuroimaging). This communication presents a simpler explanation for the results presented in Vaadia et al., by noting they are consistent with the correlated expression of stereotyped neuronal transients following (or preceding) a salient event. This re-formulation is important because: (i) correlations measured in terms of transients are not time-dependent, allowing prevailing models of neural coding to be 'reinstated'; and (ii) it suggests a powerful analysis based on singular value decomposition of firing rates.