Performance and function meet structure: A white matter brain connection tuned for motor speech control

Abstract

Despite bilateral brain activation during speech tasks, we have shown that performance is predicted by a blood flow increase in the left inferior frontal region and decrease in the right caudate, consistent with classic lesion studies. This study characterized the structural connections between these brain areas using diffusion tensor imaging and examined their relationships with measures of motor speech control. Probabilistic tractography estimated the connection strength between these two brain structures, both ipsilaterally and contralaterally, in 25 normal subjects. Speech was recorded at a separate evaluation. The majority of fiber connections were ipsilateral, but contralateral connections were also present. The relative connection strength between the right caudate and the left inferior frontal region was significantly associated with acoustic measures of stability for frequency (correlations for the repetition of /pa/ = 0.46; /ta/ = 0.5; /ka/ = 0.46; /pataka/ = 0.52) and amplitude (/pa/ = 0.43; /ta/ = 0.5; /ka/ = 0.49; /pataka/ = 0.49), echoing the predictive value of blood flow in these regions during speech. This was not observed for other connections. These results suggest that white matter connections share functional specialization with the structures they connect in the motor-speech system.