Validation of task-related excess of spike coincidences based on NeuroXidence

One of the key findings supporting the assembly hypothesis was found in recordings from the primary motor cortex of behaving monkeys involved in a delayed pointing task [A. Riehle, S. Grün, M. Diesmann, A. Aertsen, Spike synchronization and rate modulation differentially involved in motor cortical function, Science 278 (1997) 1950–1953]. Based on the unitary event (‘UE’) method, the authors have shown that excess coincidences between simultaneously recorded neurons occur dynamically at behaviorally relevant points in time. However, sensitivity of the UE method for non-stationarities and regularity of spike trains caused fear that the results presented might be, at least in part, false positives. We reanalyzed the same data with the new non-parametric method NeuroXidence, which is robust against firing-rate modulations, rate changes across trials, regularity or burstiness, as well as low rates. Our results based on NeuroXidence confirm the results presented in Riehle et al. [Spike synchronization and rate modulation differentially involved in motor cortical function, Science 278 (1997) 1950–1953] and demonstrate behaviorally modulated excesses of coincidences on a time scale of 3–5 ms.