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Time course of forepaw stimulation. (a) At each wavelength, the procedure consisted of four periods: two resting periods (P1 and P3) and two stimulation periods (P2 and P4). Each period lasted for 3 min. (b) Each stimulation period consisted of a train of electrical pulses with an amplitude of 2 mA, a pulse width of 0.25 sec and a repetition rate of 2 Hz.
