Structural and functional adaptations of the Auditory-Motor System : insights from expertise & disorder

Abstract

While evidence from clinical and functional neuroimaging domains converges on a notion that auditory-motor networks can be remodeled functionally and structurally in response to experiences, studies that seek to evaluate these hypotheses by combining behavioral, functional, and structural measures are rare. Given relatively recent advances in neuroimaging, e.g. diffusion-tensor imaging (DTI) and functional neuroimaging methods (fMRI), it is now possible to structurally and functionally analyze these networks, as well as make inferences about them in situations where the networks are either functionally compromised by an auditory-motor feedback disorder, or structurally enhanced by an intense long-term auditory-motor training regimen. To this end, a three-fold course of study has been undertaken: (1) a between-group comparison of the structural aspects of the arcuate fasciculus (a prominent white-matter fiber tract that reciprocally connects the temporal and inferior frontal lobes and is thought to be important for auditory-motor interactions) of singers and those of matched nonsinging musicians, in order to evaluate the hypothesis that singers will exhibit structural differences specifically for aspects of vocal output that require rapid temporal processing and precise sound-motor matching. (2) a within-subject fMRI comparison of responses of young adults (non-musicians) to auditory feedback that is either unperturbed or shifted in pitch while they perform a pitch-matching task, to ascertain a functional network related to perceiving and perhaps compensating for mismatched auditory feedback. (3) a within-subject pilot study of the network ascertained in (2), now in a smaller group of young adults with an auditory-motor disorder/disconnection syndrome commonly referred to as tonedeafness (TD) or congential amusia (a conditioned marked by a high pitch discrimination threshold as well as readily apparent difficulty in matching pitches), in order to provide insight into how this network might behave in a state of long-term disorder. While this work corroborates previous work in clinical, behavioral, and neuroimaging domains, and sheds light on the organization of these auditory-motor networks (structurally and functionally) in the normal population, it also aids in understanding how these networks may be remodeled and optimized (structurally) in response to intense long-term training, how they adapt to an acutely compromised state (i.e. when input to the network is compromised or perturbed), as well as how they may adapt functionally in a chronically compromised state (i.e. tonedeafness). Taken together, these observations help to explain the functioning of the auditory-motor network in normal individuals and those with communication disorders, as well as well as shedding light on possible mechanisms of recovery as they participate in an intensive long-term auditory-motor therapy program.