Rhythmic active touch, such as whisking, evokes a periodic reference spike train
along which the timing of a novel stimulus, induced, for example, when the whiskers hit
an external object, can be interpreted. Previous work supports the hypothesis that the
whisking-induced spike train entrains a neural implementation of a phase-locked loop (NPLL)
in the vibrissal system. Here we extend this work and explore how the entrained NPLL decodes
the delay of the novel, contact-induced stimulus and facilitates object localization.
We consider two implementations of NPLLs, which are based on a single neuron or a neural circuit,
respectively, and evaluate the resulting temporal decoding capabilities. Depending on the structure
of the NPLL, it can lock in either a phase- or co-phase-sensitive mode, which is sensitive to the
timing of the input with respect to the beginning of either the current or the next cycle,
respectively. The co-phase-sensitive mode is shown to be unique to circuit-based NPLLs.
Concentrating on temporal decoding in the vibrissal system of rats, we conclude that both the
nature of the information processing task and the response characteristics suggest that the
computation is sensitive to the co-phase. Consequently, we suggest that the underlying thalamocortical
loop should implement a circuit-based NPLL.