DYNAMICS OF NEURONAL INTERACTIONS CANNOT BE EXPLAINED BY NEURONAL TRANSIENTS

In a recent paper, Vaadia et al. demonstrated that patterns of firing correlation between single neurons in the cortex of behaving monkeys c an be modified within a fraction of a second. These changes occur in r elation to sensory stimuli and behavioral events, and even without mod ulations of the neurons' firing rates. These findings call for a revis ion of prevailing models of neural coding that solely rely on single n euron firing rates. In a defense of these models, Friston put forward an alternative explanation, proposing that the observed correlation dy namics emerge solely from co-modulations of the firing rates of each o f the neurons, while the strength of their interaction remains constan t. To test this possibility we re-examined the data, adopting Friston' s 'neuronal transients' model, and the associated equations and proced ures. We found that, to explain the dynamic correlation between a pair of neurons, the alternative interpretation requires that each neuron' s response to a single stimulus is composed of a relatively large numb er of independent components, which co-vary with their counterparts in the companion neuron. This large number of components and their shape s lead us to conclude that, although in principle possible, the neuron al transients model: (i) does not provide a simpler explanation of the experimental results; and (ii) cannot explain these results without i tself deviating significantly from most rate code models.