Page 31 - Summer 2010

Fig. 2. Tractography results from a) a non-tone-deaf individual, and b) a tone-deaf individual, showing distinct branches of the arcuate fasciculus. Pink and yellow are tracts identified in the left hemisphere, whereas red and green are tracts identified in the right hemisphere.
Brain-stimulation affects pitch production, simulating tone-deafness
Although the neuroimaging results are striking and robust, they provide only correlational evidence rather than causal evidence for superior temporal regions, inferior frontal regions, and the arcuate fasciculus as a pitch percep- tion and production network. To show that the grey matter regions in frontal and temporal regions are necessary for accurate pitch production, an experimental intervention is required where the hypothetical pitch production network is disrupted in a controlled manner. To this end, a recent study in our lab (Loui et al., 2010) tested the causal role of superior temporal and inferior frontal gyri in pitch production using noninvasive brain stimulation as an intervention method. In this study, we measured pitch matching behavior before and after delivering temporary stimulation to superior temporal and inferior frontal regions using transcranial direct current stimulation (tDCS). TDCS is a noninvasive brain stimulation technique that modulates the firing rate of neurons by low- current stimulation applied through electrodes attached to the surface of the scalp (for a review, see Wagner et al., 2007). Previous studies have shown selective but temporary impair- ment of cortex underlying the targeted stimulation in motor and cognitive tasks (Vines et al., 2006a; Vines et al., 2006b; Cerruti and Schlaug, 2008). Pitch production accuracy, as measured by the mean deviation between produced frequen- cy and target frequency, was disrupted following noninvasive brain stimulation, with effects being most robust after stimu- lation to the left inferior frontal gyrus. By inducing disrup- tions in pitch production behavior through the reverse-engi- neering approach of noninvasive brain stimulation, these results are important in establishing a causal role of the tem- poral and frontal brain network in pitch production. The observed results in pitch matching parallel results obtained from tone-deaf individuals, who show obvious impairments
in pitch matching (Loui et al., 2008; Dalla Bella et al., 2009; Hutchins et al., 2010). The brain-stimulation data suggest that accurate pitch production requires a distributed cortical network including superior temporal and inferior frontal areas.
Singing changes autonomic and central nervous systems—brain differences in trained singers
Pitch production is only one of several crucial basic com- ponents of singing. In the central nervous system, singing requires multiple stages of perceptual, cognitive, and motor operations. First, the brain must form an accurate mental representation of the target sounds to be produced. Then, a motor plan that matches the target mental representation has to be selected and executed. After the motor plan is executed, the auditory system must perceive feedback from one’s own voice so that vocal output can be fine-tuned in real time. These mental operations must be performed on both the rhythmic and melodic components of music, which are hypothesized to have different representations in long-term memory (Hebert and Peretz, 1997), but both components are important for singing or for music making more generally.
Due to the requirements that singing places on the cen- tral nervous system, there is mounting evidence that vocal training changes the brain in structure and function. In a functional MRI study, experienced opera singers showed dif- ferences in functional activation in the inferior parietal lobes and bilateral dorsolateral prefrontal cortex compared to non- singers (Kleber et al., 2009). In a DTI study in our lab (Halwani et al., submitted 2010), we compared the arcuate fasciculus of experienced singers against instrumental musi- cians with similar durations of musical training. Figure 3 shows group results from this study, with averaged arcuate fasciculi in 10 singers in Fig. 3a and 10 control musicians in Fig. 3b. As the figure shows, singers possess larger tract vol-
30 Acoustics Today, July 2010