The set of values of the amplitude of the narrow-band noise and its center frequency GSK-3 activation at each reversal defined the PTC. Subjects were trained on the task for 2–4 h for both the 1000- and the 2000-Hz test tones to give consistent performance before

the stimulation sessions. After training, PTCs were measured during two sessions in which either anodal or sham tDCS stimulation was applied for 20 min while subjects completed the task. In each experimental session, subjects first practised the task for 10 min, once for each 1000- and 2000-Hz test tone, before stimulation was applied. Two PTCs were determined for each test tone to give stable measurements, resulting in four PTC determinations per session. Anodal or sham stimulation was applied during four 5-min PTC determinations. All subjects had one anodal tDCS and one sham session with

the order of stimulation counterbalanced. Sessions were separated by a week to avoid any carry-over stimulation effects. Each session lasted approximately 45 min with PTC measurements taking 20–25 min. A rolling average of the amplitude of the narrow-band noise and its center frequency of two successive reversals was used to smooth the PTC and the frequency of the lowest point of the smoothed function (the LP) was found. The low-frequency slope was defined as 0.75× LP to LP and the high-frequency slope was defined as LP to 1.25× LP. Separate PR-171 price rounded exponential (roex(p)) functions were fitted to low- and high-frequency slopes using the equation (described in Patterson et al., 1982) for each slope: (1) where W is the shape of the PTC, g is the normalized deviation from the center frequency, p is the slope of the function and r is the shallower tail of the function. This produces low- and high-frequency slopes of the PTCs, with higher values indicating steeper slopes. The arithmetic mean for the low- and high-frequency slopes of the two determinations for each

fc was taken. Equivalent rectangular bandwidths (ERBs) were determined using the products of the roex(p) fitting with the equation (Moore, 1995): (2) where fc is the frequency of the tone, pl is the slope of the low-frequency equation and pu is the slope of the high-frequency equation. Data were normally distributed and suitable for parametric analysis. The second follow-up experiment measured the effects Pregnenolone of anodal tDCS on temporal fine structure (TFS), which is dependent on the fidelity of temporal coding information (Rose et al., 1967). The experimental design was similar to Experiment 2A with TFS measured in separate tDCS and sham stimulation sessions for each subject. Sensitivity to TFS was measured using the method described in Hopkins & Moore (2007) and Moore & Sęk (2009). This method estimates a TFS threshold using an adaptive 2I-2AFC procedure with a two-up, one-down rule estimating the 70.7% point on the psychometric function (Levitt, 1971).