Single 2-spike burst induces robust STP. (A) Stimulation paradigms used at times corresponding to letters shown on plot below. (B) At “a,” induction consisted of coincident stimulation of a single subthreshold fEPSP (indicated by single vertical line, Pathway 1) with a brief burst (5 stimuli at 100 Hz) (indicated by arrow in Pathway 2) in an independent pathway. At “b,” two test stimuli (33 Hz, indicated by closely spaced vertical lines) were used in Pathway 1. At “c,” the two test stimuli preceded the 100-Hz burst by 20 msec. Inset is an overlay of fEPSPs from Pathway 1 just prior to (thin trace) and following (thick trace) induction paradigms at “a,” “b,” and “c.” Calibration bars correspond to 5 msec and 200 µV.