I suggest that an objective identification of the cell assembly requires two key conditions: a reader-classifier and a temporal frame. Neurons come together in transient time frames to produce a composite downstream effect, which cannot be achieved by single neurons alone. The most important modus operandi in this process is synchrony of events (Abeles 1991; Engel et al., 2001; Fries et al., 2007; Hansel and Sompolinsky, 1992; Singer 1999). In its broad definition, synchrony refers to the concurrence of events in time. However, this definition of synchrony is meaningful only from the perspective of a reader mechanism with the ability to integrate upstream events over time (Buzsáki 2006). Thus, whether events are synchronous or not can be determined only by their impact on a reader-actuator. Similarly, I suggest that the cell assembly can only be defined from the perspective of a reader mechanism.
