Behavioral effects arising from the neural substrates for atypical planning and execution of word production in stuttering

Abstract

This article reports on an fMRI study that examined the neural bases of atypical planning and execution processes involved in stuttering (Lu et al., 2010). In the study, twelve stuttering speakers and 12 controls named pictures which required single-syllable, multi-syllable, or repeated-syllable word responses, in the scanner. The factors associated with planning and execution were: (1) number of syllable-sized motor programs; and (2) syllable size and onset complexity. Structural equation modeling revealed two parallel neural circuits (the basal ganglia-inferior frontal gyrus, premotor area circuit and the cerebellum-premotor area circuit). These were involved in atypical planning and execution processes in stuttering, respectively. The interface between planning and execution in stuttering involved the angular gyrus. This article discusses the relevance of these findings to behavioral theories that also propose separate planning and execution mechanisms behind stuttering.

Figure 1

Diagrammatic representation of the temporal relationship (x axis) between planning and execution when a speaker stalls (top part) or advances (bottom part) according to the EXPLAN model. For both parts, planning of three successive words is shown in the top rows of each part (two short words to plan and one long word to plan, labeled word n, n+1 and n+2). Execution of word n commencing after its plan is complete as shown in the second rows of each part. While word n is being executed, there is sufficient time to plan the following word (n+1). Word n+1 is executed immediately after word n has been completed and planning for word n+2 commences. At the point where execution of word n+1 is complete, the plan for word n+2 is not finished. In the top part for the case where the speaker stalls, the speaker repeats word n+1 and this allows sufficient time to complete the plan of word n+2 (that word can then be produced and the utterance continued). In the bottom part for the case where the speaker advances his or her speech (i.e. starts the utterance with an incomplete plan), the plan may run out in which case the speaker may sustain the first part of word n+2 (prolongation), repeat it (part-word repetition) or interrupt it (word break).