0.7 Music, biological evolution, and the brain  (Page 19/30)

I hypothesize that one set of mechanisms involves the neuroendocrine system, i.e., the regulation of hormones by the brain. Music appears to have a strong influence on the human limbic system (Peretz, 2010; Koelsch, 2010), an emotional regulation system with diverse subcortical (e.g., hippocampus, amygdala, cingulate) and cortical (e.g. orbitofrontal cortex) components, which is influenced by many descending inputs from wide regions of the cerebral cortex (Damasio, 1994). The mechanisms by which music influences the limbic system remain to be understood and may revolve in part around music’s ability to emulate emotionally significant vocal sounds (Juslin and Laukka, 2003; Snowdon and Teie, 2009), though this is clearly only part of the story. For the current purposes, the crucial point is that the limbic system projects to the hypothalamus, which in turn regulates the release of a broad range of hormones from the brain and various peripheral glands (e.g., oxytocin, cortisol, etc.). Hormones are blood-borne chemical messengers that can have long-lasting effects on a range of brain structures that have hormone receptors. For example, the hippocampus and amygdala have cortisol receptors, and chronically elevated cortisol (e.g., due to prolonged stress) can influence neuronal morphology and activity in these brain structures, as well as the birth of new cells in the adult hippocampus (Sapolsky, 2000). Since there is empirical evidence that listening to music can transiently reduce cortisol levels in adults and infants (Trehub and Nakata, 2002; Khalfa et al., 2003; Suda et al., 2008), this suggests one pathway by which regular musical listening may have lasting effects on the brain (cf. section 4.1 above). Of course, cortisol is just one hormone regulated by the brain, and it seems likely that many hormones (e.g., testosterone, vasopressin, etc.) are potentially influenced by music (Fukui et al., 2008). In all such cases, the critical point is that hormones can have long-lasting effects on the cells that they influence. Thus, neuroendocrine effects on the brain are conceptually and mechanistically distinct from transient neurotransmitter effects, e.g., the release of dopamine associated with musical chills (“goosebumps”) (Blood and Zatorre, 2001; Salimpoor et al., 2009).

Of course, the fact that hormones can have long-lasting effects on brain structure or function does not mean that they always do have such effects. The degree to which neuroendocrine effects result in lasting changes to the brain likely depends on the state the brain is in when such effects occur. Rapidly changing nervous systems (e.g., the brains of healthy infants or of older adults in the period soon after a brain injury) may be particularly sensitive in this regard. Furthermore, there may be genetic factors (including variation in hormone receptor density) that influence tissue sensitivity to hormones.

Apart from neuroendocrine effects, I hypothesize that another way music can have lasting effects on nonmusical abilities is via mechanisms of neural plasticity, i.e. via use-dependent functional or structural changes in brain circuitry. (In contrast to neuroendocrine mechanisms, which can be activated by passive listening to music, plasticity-based mechanisms are likely to be driven by active engagement with music, e.g. via regular singing or playing of a musical instrument.) Modern neuroscience has shifted from a view of the brain as plastic only during early developmental periods to a view that recognizes a substantial degree of plasticity throughout the lifespan (Edelman, 1987; Draganski and May, 2008). The “permanent plasticity” of the brain means that the networks involved in our cognitive functions are malleable throughout life (though the degree of malleability in many brain areas may be substantially higher during early sensitive periods of development). According to TTM theory, music engages processing mechanisms shared with a wide range of cognitive domains, such as language, attention, auditory scene analysis, and so forth. Hence, music has the opportunity to influence these domains by driving plasticity in brain networks that it shares with these domains.