Page 30 - WINTER2019

Music and the Brain
Figure 1. A: approximate spatial and temporal resolution of neural recording methods. EEG, electroencephalography; MEG, magnetoencephalography: fMRI, functional magnetic resonance imaging; PET, positron emission tomography. B: EEG methods provide good temporal but limited spatial resolution. Top: early right anterior negativity. From Loui et al. (2005). Bottom: bird’s-eye view of the EEG recording setup. C: fMRI methods provide good spatial but lower temporal resolution. Top: brain activity in auditory cortices, as observed during music listening. From Loui et al. (2012). Bottom: MRI setup.
EEG can also register activity from way stations in the audi- tory brainstem. This auditory brainstem response (ABR) is particularly accurate at discriminating between different sounds. Because it is a stimulus-driven response, the ABR resembles the stimulus itself, and this stimulus-brain resem- blance is taken as a neural marker of the fidelity with which the auditory brainstem codes for sounds. Importantly, the fidelity of ABR in encoding sounds is higher in musically trained participants (Kraus and Chandrasekaran, 2010). The musicians’ advantage in neural encoding, as indexed with the ABR, has been observed for a variety of sounds includ- ing speech as well as music and in older adults as well as in children.
Although EEG can resolve fine-grained temporal details in brain activity, it is relatively limited in its ability to locate the source of the neural response in the brain, or spatial resolu- tion. Some boost in spatial resolution comes from recording with MEG, which records the magnetic fluctuations that accompany electrical changes in the activity of neural popu- lations. MEG provides the same temporal resolution as EEG, but because it is not constrained by the arrangement of scalp sensors, it shows a relative increase in spatial resolution, par- ticularly in its ability to measure activity from the inward folds, known as sulci, on the surface of the brain. Thus, music researchers who are interested in auditory sources of brain
activity are able to map these sources with increased spatio- temporal resolution.
Although EEG and MEG offer good temporal resolution, structural and functional MRI offer superior spatial reso- lution. Functional MRI captures the oxygenation level of blood as required by neural activity (Figure 1C). Structural MRI includes anatomical and diffusion images, among others. Anatomical images are effective at comparing the relative volume, cortical thickness, and surface area of cor- tical and subcortical structures in gray matter cell bodies (neurons) as well as identifying any lesions such as those due to stroke or traumatic brain injury. Diffusion images are useful for visualizing the white matter pathways, which consist of bundles of axons that connect the neuronal cell bodies in the brain.
Pitch
Pitch is a basic building block of music. It is the perceptual attribute of sound that most closely maps on the fundamental frequency (f0). This psychological attribute of pitch ranges from low to high, and two sounds can have the same pitch despite having energy at different frequencies, as long as the f0 is the same. Musical training seems to hone a finer grained ability to discriminate between small differences in pitch because classical musicians have frequency discrimination
30 | Acoustics Today | Winter 2019