Musical Disorders: From Behavior to Genes

Research over the last decade has provided compelling evidence that the ability to engage with music is a fundamental human trait, yet the biological basis of music remains largely unknown. Recent findings indicate that a small number of individuals have severe musical problems that have neurogenetic underpinnings. Such deficiencies are termed congenital amusia, an umbrella term for lifelong musical disabilities that cannot be attributed to mental retardation, deafness, lack of exposure to music, or brain damage after birth. Congenital amusia constitutes a natural experiment, giving us a rare chance to examine the biological basis of music by tracing causal links among genes, environment, brain, and behavior. KEYWORDS—congenital amusia; music cognition; musical brain; musical genes; tone deafness Humans are born with the potential to both speak and make music. For the musically untrained majority, this fundamental human trait is expressed by avid listening and occasional dancing and singing. The propensity to engage in music ultimately gives rise to a sophisticated music processing system that is largely acquired implicitly by experience (Peretz, 2006). However, a minority of individuals never acquire this core musical system, either in part or in total. This condition affects 4% of the general population (Kalmus & Fry, 1980). It has been variously called note deafness, tone deafness, tune deafness, dysmelodia, and, more recently, congenital amusia (Peretz & Hyde, 2003). All of these terms refer to the same condition: A lifelong deficit in melody perception and production that cannot be explained by hearing loss, brain damage, intellectual deficiencies, or lack of music exposure. I coined the term congenital amusia to acknowledge the possibility that there may exist as many forms of congenital amusias as there are forms of acquired amusias, which arise as the consequences of accidental brain damage. The term congenital means simply ‘‘present from birth’’; it defines a likely time period but not the etiology. Recent research has made major progress, however, regarding the etiology of this disorder. The goal of the present article is to summarize the current evidence. The main reason for studying congenital amusia is that such disorders offer unique insight into the behavioral, neural, and genetic bases of cognitive functions in general and of music cognition in particular. The framework adopted here closely follows that of work conducted on language disorders (e.g., Bishop & Snowling, 2004). It makes a distinction between observed behavior, cognitive processes, neurobiology, and etiology. Like language, musical abilities result from genes and environmental factors that guide brain development and shape cognitive functions by affecting neural processes such as migration of neurons, cell death, and connectivity. An anomaly observed at the behavioral level can be traced back to cognitive processes, then to brain processes, and ultimately to genes and environment. As indicated in Figure 1, anomalous behavior may also influence the environment, such that the effect is somewhat circular. For example, an amusic person may avoid challenging musical situations and, consequently, live in a musically impoverished environment. It is also possible that amusic children seek music training to compensate for their difficulties, such that by adulthood they may no longer appear to have a severe problem. Both situations would have deep influences on brain and cognition. In short, the paths from etiology to cognition via neurobiology are not simple, but they are tractable, as illustrated here with congenital amusia.