Cortical activity associated with rhythmic grouping of pitch sequences

Segmentational grouping in music listening refers to the organisation of individual tones into tone groups that tend to be processed and subsequently recalled as perceptual units or chunks. Grouping of tones via this process tends to occur at natural breaks in structure of a tone sequence, so that relatively larger changes in pitch, amplitude or timing are perceived as boundaries which cue the segmentational grouping process. Segmentational grouping processes have been examined using behavioural research techniques; yet neurophysiological processes underlying the grouping process have received little attention, and are poorly understood. This study aimed to identify brain regions involved in the segmentational grouping process as cued by rhythmic information. Participants performed two auditory tasks while brain electrical activity responses were monitored using Steady-State Probe Topography (SSPT). Behavioural responses evoked in a task probing individuals' use of lengthened-duration tones to organise memory for pitch sequences indicated that longer-duration tones were used as cues to organise working memory representations of the musical patterns. Examination of dynamic SSPT responses during the encoding phase of a probe recognition task indicated that greater use of rhythmic cues to organise working memory representations was associated with activation of a network of left hemisphere frontal, temporal and parietal regions. During the lengthened tone, activation of left central and vertex regions and progressive activation of left temporal and temporoparietal regions were linked with use of the deviant status of the lengthened tone to update temporal expectations for the sequence. Excitatory responses observed in left posterior frontal and temporal regions to a tone following the lengthened tone were proposed to reflect temporal allocation of attention to this point in time, whereas sustained excitatory activation of left temporal, and temporoparietal regions reflected the role of these regions in supporting representations of the tone events in working memory. Finally, late inhibitory responses to the tone following the lengthened tone in left frontal, temporal, temporoparietal, and parietal regions were linked with the manipulation and closure of the working memory trace in association with the grouping process. Together, these findings support the activation of a network of left frontal, temporal and parietal regions underlying rhythmic grouping of pitch sequences.