Sleep-dependent neuroplastic changes during auditory perceptual learning

Auditory perceptual learning is accompanied by a significant increase in the amplitude of sensory evoked responses on the second day of training. This is thought to reflect memory consolidation after the first practice session. However, it is unclear whether the changes in sensory evoked responses depend on sleep per se or whether a break between training sessions would sufficiently yield similar changes. To assess the relative contributions of sleep and passage of time (wakefulness) on the sensory evoked responses, we recorded auditory evoked fields using magnetoencephalography while participants performed a vowel segregation task in three different sessions separated by 12h over two consecutive days. The first two practice sessions were scheduled in the morning and evening of the same day for one group and the evening and morning of subsequent days for the other group. For each participant, we modeled the auditory evoked magnetic field with single dipoles in bilateral superior temporal planes. We then examined the amplitudes and latencies of the resulting source waveforms as a function of sleep and passage of time. In both groups, performance gradually improved with repeated testing. Auditory learning was paralleled by increased sustained field between 250 and 350ms after sound onset as well as sensory evoked fields around 200ms after sound onset (i.e., P2m amplitude) for sessions taking place on the same and different days, respectively. These neuromagnetic changes suggest that auditory learning involves a consolidation phase that occurs during the wake state, which is followed by a sleep-dependent consolidation stage indexed by the P2m amplitude.