Fig. 3.

Individual examples of eyeblink mechanograms in a treatment (TTX) and control (PBS) rabbit during the CS-alone retention test and the first paired-stimuli session (100 trials) of Acquisition phase II. Each stack plot represents a complete printout from a single training session and each trace represents one trial. The uppermost trace (begin) is the first trial of the session. Upward deflections in the eyeblink traces indicate eye closure. The wide gap within each plot separates CS-alone from paired CS+US trials. Vertical lines in each plot denote CS and US onsets. Eyeblinks after the CS mark in the first 40 trials and those between the CS and US marks after trial 40 were considered CRs (see Methods section for details). During CS-alone trials, the TTX rabbit exhibited sparse, small-amplitude blinks, whereas the PBS rabbit expressed a much larger number of well-formed CRs at the beginning with extinction toward the end of session. During CS+US training, the PBS rabbit re-acquired a robust level of CRs. In contrast, the TTX rabbit had no CRs at the beginning of the session and then slowly acquired small-amplitude CRs.