Figure 1.

The temporal sequence of the experimental task. Pairs of noxious heat or innocuous cool stimuli were applied to the back of the lower leg. Before the termination of the second stimulus (T2: 48, 48.5, 49, 50°C for noxious heat, 20, 15°C for innocuous cool), subjects had to indicate that the intensity of T2 was the same or was different from that of the first stimulus (T1: 48°C for noxious heat, 20°C for innocuous cool). Discrimination-related brain activity was identified using regressors determined by the duration of the evaluation (i.e., response latency) of pairs of equally intense stimuli (48°C–48°C or 20°C–20°C). Additional regressors were used to identify brain activation that was related to memory and to perceived pain (or cool).