Beta-Band Oscillations Represent Auditory Beat and Its Metrical Hierarchy in Perception and Imagery

Abstract

Dancing to music involves synchronized movements, which can be at the basic beat level or higher hierarchical metrical levels, as in a march (groups of two basic beats, one-two-one-two …) or waltz (groups of three basic beats, one-two-three-one-two-three …). Our previous human magnetoencephalography studies revealed that the subjective sense of meter influences auditory evoked responses phase locked to the stimulus. Moreover, the timing of metronome clicks was represented in periodic modulation of induced (non-phase locked) β-band (13-30 Hz) oscillation in bilateral auditory and sensorimotor cortices. Here, we further examine whether acoustically accented and subjectively imagined metric processing in march and waltz contexts during listening to isochronous beats were reflected in neuromagnetic β-band activity recorded from young adult musicians. First, we replicated previous findings of beat-related β-power decrease at 200 ms after the beat followed by a predictive increase toward the onset of the next beat. Second, we showed that the β decrease was significantly influenced by the metrical structure, as reflected by differences across beat type for both perception and imagery conditions. Specifically, the β-power decrease associated with imagined downbeats (the count "one") was larger than that for both the upbeat (preceding the count "one") in the march, and for the middle beat in the waltz. Moreover, beamformer source analysis for the whole brain volume revealed that the metric contrasts involved auditory and sensorimotor cortices; frontal, parietal, and inferior temporal lobes; and cerebellum. We suggest that the observed β-band activities reflect a translation of timing information to auditory-motor coordination.

Significance statement: With magnetoencephalography, we examined β-band oscillatory activities around 20 Hz while participants listened to metronome beats and imagined musical meters such as a march and waltz. We demonstrated that β-band event-related desynchronization in the auditory cortex differentiates between beat positions, specifically between downbeats and the following beat. This is the first demonstration of β-band oscillations related to hierarchical and internalized timing information. Moreover, the meter representation in the β oscillations was widespread across the brain, including sensorimotor and premotor cortices, parietal lobe, and cerebellum. The results extend current understanding of the role of β oscillations in neural processing of predictive timing.

Keywords: ERD; event-related desynchronization; magnetoencephalography; predictive coding; timing processing.

Copyright © 2015 the authors 0270-6474/15/3515187-12$15.00/0.

Figures

Figure 1.

Time courses of click stimuli and auditory evoked responses, grand averaged across left and right cortical sources and across all participants. Twenty-four isochronous clicks were used as auditory stimuli with an onset-to-onset interval of 390 ms. A, In the march condition, the first half of the stimulus sequence imposed the meter structure by acoustically accenting every second click. In this interval, the participants were instructed to perceive the march meter. The second half of the sequence remained at the softer intensity throughout. Here the participants had to imagine the meter structure subjectively. The evoked P1 was prominently expressed in response to each beat stimulus. In the perception interval, the auditory evoked N1 response was predominantly expressed for the accented downbeat stimuli only, whereas during the imagery interval, the evoked N1 was very small for all beats. B, For the waltz condition, every third stimulus was accented. Again, P1 responses were prominent to each beat and N1 responses followed the physically accented stimuli.

Figure 2.

Oscillatory activities related to the beat in the left and right auditory cortices, obtained by averaging across all beat and meter types. Spectral power changes were referenced to the mean across the beat interval. A, The original TFR for all the beat types averaged from the accented “perception” stimulus interval. The signal power increase at ∼100 ms latency between 5 and 15 Hz reflects spectral power of the auditory evoked response, which is enhanced by the acoustically accented beats. B, The TFR during the unaccented imagery stimulus interval. This contains less contribution from the evoked response because all the stimuli are unaccented. C, D, Induced oscillatory activities expressed in the TFRs in which the spectral power of the averaged evoked response was subtracted before averaging, thus leaving only non-phase-locked signal power changes. E, F, Time series of β modulation in the 15–25 Hz band. The β-ERD was referenced to the maximum amplitude at ∼50 ms latency.

Figure 3.

Induced oscillatory activity in the left and right auditory cortex for the march condition. A, B, Time-frequency representation of the auditory source activity in the perception and imagery conditions, respectively, in the left (A) and right hemispheres (B). C, D, Time course of modulation of β-band activity in the left (C) and right hemispheres (D). The shaded area represents the 95% confidence interval of the group mean.

Figure 4.

Induced oscillatory activity in the left and right auditory cortex for the waltz condition. A, B, Time-frequency representation of the auditory source activity in the perception and imagery conditions, respectively, in the left (A) and right hemispheres (B). C, D, Time course of modulation of β-band activity in the left (C) and right hemispheres (D). The shaded area represents the 95% confidence interval of the group mean.

Figure 5.

The results of the PLS analysis for the β-band power that characterizes the contrast between the different beat types in the march condition. The LV1 represents the contrast between the downbeat and upbeat (left, top), which was significant in both march perception and march imagery conditions. The corresponding brain areas in the march perception condition (right, top) demonstrate only the cool colored voxels, in which the β power is decreased for the downbeat compared to the upbeat. In the march imagery condition (bottom), the associated brain areas (right) show both cool colored area (downbeat β decrease > upbeat β decrease) and warm colored areas (e.g., downbeat β decrease

Figure 6.

The results of the PLS analysis for the β-band power that characterizes the contrast between the different beat types in the waltz condition. A, The LV1 related to the contrast between the downbeat and upbeat (left) was only significant in the waltz perception condition. The corresponding brain areas (right) demonstrate the blue colored voxels, in which the β power is more decreased for the downbeat compared to the upbeat, and the red colored areas, representing the opposite pattern. B, The LV2 related to the contrast between the middle beat and upbeat (left) was significant for both the waltz perception and waltz imagery conditions, yielding the associated brain areas (right). Note that for the LV2, in both perception and imagery, the only brain areas above the significance level were associated with the larger β-power decrease for the upbeat, compared to the middle beat. The list of the locations and Talairach coordinates are indicated in Table 2. Cg, Cingulate; Crb, cerebellum; FFG, fusiform gyrus; Ins, insula; MedFG, medial frontal gyrus; MFG, middle frontal gyrus; MTG, middle temporal gyrus; PCL, paracentral lobule; PostCG, postcentral gyrus; PreCG, precentral gyrus; PreCu, precuneus; SFG, superior frontal gyrus; Th, thalamus; TTG, transverse temporal gyrus.