To musicians, the message is in the meter: Pre-attentive neuronal responses to incongruent rhythm are left-lateralized in musicians
Introduction
Music is one of the many ways humans communicate with each other. Whether music and verbal language share neuronal networks or music is processed in separate brain modules holds the key to understanding music in an evolutionary perspective (Huron, 2001), as well as music in the context of human communication. Hence, this issue has been hotly debated in the growing field of neuro-biological research in music.
In support of neural dissociation between music and language processing, lesion studies and studies of people suffering from acquired and congenital amusia show a double dissociation between aspects of music and language processing (Ayotte et al., 2000, Liegeois-Chauvel et al., 1998, Mendez, 2001, Peretz and Coltheart, 2003, Peretz et al., 1994, Peretz et al., 2002) as well as a greater involvement of the right hemisphere in basic music processing of especially pitch-related features (Samson et al., 2002, Tervaniemi and Hugdahl, 2003, Zatorre, 1988, Zatorre et al., 2002). Brain responses to auditory stimuli, however, are not only determined by physical properties of the stimuli, and the nature of cognitive operations involved. In many cases, the listeners' competence and familiarity with the stimuli affect neuronal processing. This has been shown for pre-attentive processing of language at 100–200 ms after stimulus onset as indicated by the mismatch negativity (MMNm), recorded with magnetoencephalography (MEG). Left lateralization of the MMNm occurs to deviating phonemes from subjects' mother tongues only (Näätänen et al., 1997), and deviating Morse code syllables in Morse code trained subjects, only (Kujala et al., 2003), suggesting that left lateralization of sounds occur when they are perceived as meaningful.
Although music—in contrast to verbal language—rarely refers to objects in the real world, musical performance involves communication. When musicians play, they exchange non-verbal signs as messages, and from this interaction, music emerges as a concrete form (Sawyer, 2004). Musical communication, for example, musical humor (Huron, 2004), is often conveyed through violation of musical expectancy. Music theory explains musical expectancy as the motion between opposites as in harmony the tension of the dominant chord resolved by the motion to the tonic. This phenomenon is referred to as an example of musical syntax and violations of the authentic cadence has been shown to activate cortical language areas (Maess et al., 2001). Anticipation of rhythmic patterns is another crucial aspect of musical expectancy. It is established by the so-called meter (Sadie et al., 2001) that provides the listener with a grid of strong and weak beats creating expectancy of rhythmic timing as well as strength. This phenomenon is well illustrated as the different feeling of a 3/4 rhythm like waltz and a 4/4 rhythm like in a blues. In jazz, deviations from the well-established rhythmic pattern are a central feature. This has obvious stylistic implications, but importantly, deviations are also means of communicating intentions and ideas in the largely improvised performance. Hence, jazz musicians receive and interpret as cues performances parting from regular rhythm patterns (Berliner, 1994, Monson, 1997, Vuust, 2000). This suggests that skilled jazz musicians may have developed a high sensitivity to subtle deviations of rhythm. To test this, we used MEG to study the strength and lateralization of pre-attentive responses of the central nervous system (MMNm) to deviations from a pattern of rhythm in expert jazz musicians and musically inept non-musicians.
Section snippets
Materials and methods
To mimic communicative cues in improvised music, we made sequences of increasingly incongruent rhythm, using realistic broadband drum sounds (Fig. 1a). The stimuli were sI, a simple 4-beat rock rhythm; sIu and sId, variations of sI with a last snare drum beat of the sequence tuned up (sIu) or down (sId); and sII and sIII, variations of sI with a weak (sII) or strong (sIII) departure from the rhythm. SII may be described as a syncopation breaking the rhythmic expectancy by replacing a weak beat
Results
Total MGA (left + right) to sIII across all subjects significantly exceeded sII (P < 0.001, T = −15.8), which in turn significantly (P = 0.01, T = 2.84) exceeded sI (sIII: 74 fT/cm, SE = 6, sII: 28 fT/cm, SE = 4 and sI: 18 fT/cm, SE = 1). Across all subjects, for each hemisphere, MGAs to sIII significantly exceeded sII (P < 0.001, left: T = 10.8, right: T = 11.9), which in turn significantly [P < 0.05, left: T = 2.17, right: T = 3.55), exceeded sI (sIII (left) 36.4 fT/cm, SE = 3.9, sII (left)
Discussion and conclusion
In the right hemisphere, the rhythm cues elicited responses of similar strength in expert and inexpert subjects. In the left hemisphere, the expert subjects responded with greater strength than in the right hemisphere, while inexpert subjects responded less rapidly and with less strength. In addition, experts responded with greater strength in the left hemisphere than inexpert subjects in the right hemisphere did. These competence-related differential activation patterns are strikingly similar
Acknowledgments
This research was supported by The Danish National Research Foundation. We thank Mads Paldam, Ville Mäkinen, and Dr. Risto Llmoniemi for their help with this study and all the musicians and nonmusicians who participated.
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