Neural Correlates of Musical Behaviors A Brief Overview

Abstract

Much of what we know (or think we know) about the brain rests on an assumption called the localization hypothesis: the brain is not just a mass of undifferentiated tissue, but rather, specific neural regions underlie distinctive behaviors, thoughts, and actions. This is reflected in the names we give to brain regions, such as motor cortex (for movement), sensory cortex (for processing information from the five senses), auditory cortex, and visual cortex. Evidence for regional specialization comes from case studies of patients with lesions, and from various neuroimaging technologies (Positron Emission Tomography, or PET; functional Magnetic Resonance Imaging, or fMRI; Magnetoencephalography, or MEG; Electroencephalography, or EEG), as well as animal studies.It is seductive to think of a one function-one brain mapping schema, whereby function x is handled specifically and exclusively by brain region y and so on. There may be some truth to this, but the situation is far more complex. The human brain is massively parallel and distributed. Although aspects of certain functions can be localized, other functions are likely to be distributed widely across different brain regions in functional circuits or networks. Lower level functions such as pitch perception are more likely to be localized to specific regions, whereas higher-level functions such as melody recognition are more likely to involve networks taking inputs from several widely dispersed regions. It is important to bear in mind these general principles when thinking about brain regions and musical activities.This paper reviews neuromusical behaviors in three domains: (1) perceptual-cognitive, including the communicative functions of music and speech, (2) emotional reactions to music, and (3) effects of music on immune function and health.Perceptual-Cognitive Processing of MusicMusic consists of six fundamental attributes: pitch, duration, loudness, timbre, spatial location, and reverberant environment (Levitin, 2010). A set of two or more pitches gives rise to contour and melody, and a set of two or more durations gives rise to rhythm. Thus, melody and rhythm are secondary aspects of these fundamental attributes.Unlike light, which is easily transmitted in a vacuum, sound requires a medium of transduction such as air or water. Pressure waves in the air (for example) stimulate the tympanic membrane (eardrum) and to some extent, the bones surrounding the ear; these pressure waves are turned into electrical signals that are transmitted to the brain. Sound can activate unconscious, reflex actions (mediated by the brain stem and pons), the most well-known of these being the startle reflex, which occurs before any conscious process alerts us of an impending danger.One striking aspect of the brain's response to sound is that the neural response to sound is isomorphic to the sound itself. In other words, if we look at the waveform of a piece of music, and then at the waveform of the brain's response to that music, the two waveforms are nearly identical. This is true for single cell recordings in the inferior colliculus (Janata, 1997) or evoked potentials of the brainstem taken from the scalp (Skoe & Kraus, 2010). In fact, the output of such brain measures can be connected to a loudspeaker, and sounds approximating the music itself can be heard (Levitin, 2007). These findings provide evidence that pitch perception, one of the foundations of music, is innately wired into our brains.Pitch is encoded at every level of the auditory system, beginning with the cochlea, inside of which exists a tonotopic (pitch by location) mapping. In other words, if we could uncoil the cochlea and flatten it out, we would see that its hair cells on one end are maximally responsive to low frequencies, hair cells on the other are maximally responsive to high frequencies, and intermediate regions are responsive to intermediate frequencies. In effect, the cochlea is laid out like a piano keyboard (but without the height differential between black keys and white keys! …