Experimental protocol.

<p>Sleep recordings were scheduled in the first night (adaptation), in the second night (baseline sleep), and in the third and fourth nights (post-paired associative stimulation sleep). In the third or fourth night subjects were submitted to a paired associative stimulation paradigm with a 25-ms interval (PAS-25), in the one night, and to a PAS paradigm with a 50-ms interval (PAS-50), in the other. The sequence of PAS-25 and PAS-50 was counterbalanced between subjects. Subjects were then retested after the final morning awakenings.