Cerebral localization of impaired phonological retrieval during rhyme judgment

Abstract

Objective: Computation of a prearticulatory phonological representation (phonological access, or phonological retrieval) is an essential process in speech production whose neural localization is not clear. This study combined a specific behavioral measure of phonological access and multivariate voxel-based lesion-symptom mapping (VLSM) in a series of left hemisphere stroke patients to identify brain regions critical for this process.

Methods: Phonological access was assessed in 40 chronic ischemic stroke patients using a silent rhyming task to avoid confounds with motor planning and articulation deficits. Additional covariates were incorporated in the VLSM analysis to control for orthographic and working memory demands of the rhyming task, and for age, education, and total lesion volume. The resulting t statistic maps were thresholded at voxelwise p < 0.001 and cluster-corrected at a familywise error of p < 0.05.

Results: Phonological access impairment was correlated with damage to a focal region of cortex and white matter caudal to the posterior sylvian fissure, which included the posterior supramarginal gyrus and adjacent anterior angular gyrus, planum temporale, and posterior superior temporal gyrus. No correlation was observed with Broca's area, insula, or sensorimotor cortex. An additional VLSM showed no correlation between damage in this posterior perisylvian region and spoken word comprehension.

Interpretation: This is the first demonstration of a specific lesion correlate for phonological access impairment. Although this posterior perisylvian region overlaps with some versions of the classical Wernicke area, the present results demonstrate its involvement in prearticulatory phonological production rather than speech perception or lexical-semantic processes.

© 2014 American Neurological Association.

Figures

Figure 1

Example trials from the behavioral tasks (actual trials were in color). Participants see a prompt in a green box signaling the start of a trial (left column). Pressing the prompt causes the choices to appear, each surrounded by a green box (right column). This display remains on the screen until the participant selects one of the choices. The top row shows an example of the Rhyme Matching task. The middle row shows an example of the Semantic Matching task. The bottom row shows an example of the Auditory Word-Picture Matching (AWPM) task. In the AWPM task, pressing the prompt causes a spoke word sound file to be played simultaneously with the appearance of the picture choices.

Figure 2

(A) T1-weighted anatomical MRI showing the lesion in one participant. (B) Lesion segment (red) obtained using the semi-automated segmentation method.

Figure 3

(A) Lesion overlap across all 40 patients, thresholded to include only voxels that were lesioned in at least 5 patients. (B–E) Primary VLSM analysis using Rhyme Matching performance as the dependent measure. (B) Unthresholded t-map, shown in serial sagittal sections through the left hemisphere. (C) T-map thresholded at p < .001, cluster-corrected at FWE of p < .05, shown in serial left sagittal, coronal (lower left), and axial (lower right) sections. Green lines indicate the locations of orthogonal sections. (D) Articulatory Agility included as an additional covariate in the VLSM of Rhyme Matching. (E) Auditory Word-Picture Matching (AWPM) included as an additional covariate in the VLSM of Rhyme Matching. (F) Composite image showing results of the final supplementary analysis with AWPM performance as the dependent measure, shown in light blue, and the primary analysis with Rhyme Matching performance as the dependent measure in red. AWPM performance is shown with relaxed voxel-wise threshold of p < .005 and cluster size threshold of 500 μl.