Amplitude and phase-locking adaptation of neural oscillation in the rat auditory cortex in response to tone sequenceTakahiro

Sensory adaptation allows stimulus sensitivity to be dynamically modulated according to stimulus statis-tics and plays pivotal roles in efficient neural computation. Here, it is hypothesized that in the auditorycortex, phase locking of local field potentials (LFPs) to test tones exhibits an adaptation property, i.e.,phase-locking adaptation, which is distinct from the amplitude adaptation of oscillatory components.Series of alternating tone sequences were applied in which the inter-tone interval (ITI) and frequencydifference (F) between successive tones were varied. Then, adaptation was characterized by the tem-poral evolution of the band-specific amplitude and phase locking evoked by the test tones. Differences aswell as similarities were revealed between amplitude and phase-locking adaptations. First, both ampli-tude and phase-locking adaptations were enhanced by short ITIs and small Fs. Second, the amplitudeadaptation was more effective in a higher frequency band, while the phase-locking adaptation was moreeffective in a lower frequency band. Third, as with the adaptation of multiunit activities (MUAs), theamplitude adaptation occurred mainly within a second, while the phase-locking showed multi-secondadaptation specifically in the gamma band for short ITI and small F conditions. Fourth, the amplitudeadaptation and phase-locking adaptation were co-modulated in a within-second time scale, while thisco-modulation was not observed in a multi-second time scale. These findings suggest that the amplitudeand phase-locking adaptations have different mechanisms and functions. The phase-locking adaptationis likely to play more crucial roles in encoding a temporal structure of stimulus than the amplitudeadaptation.