Objective:

The goal of this project is to elucidate the areas of the brain involved in phonological working memory using Voxel-Based Lesion Activity Mapping (VLAM).

Background:

According to the dual stream model of language, the ventral stream is involved with mapping sound to meaning. The dorsal stream is specialized for mapping sound onto articulatory-based representations (ie phonological processing). Literature in behavioral neuropsychology, aphasia, and neurosurgical stimulation provide evidence that phonological working memory and language repetition is supported by the dorsal stream. However, connectivity-level evidence for this claim is lacking.

Design/Methods:

We investigated the regions of the brain involved in phonological working using a technique called Voxel-based Lesion Activity Mapping (VLAM). In VLAM, the presence or absence of a lesion at each voxel of the brain is related to variability in neural activity in a reference region. 55 participants with brain tumor performed sentence and word repetition tasks. By examining the lesion sites which lead to reduced activity in speech-motor cortex, during repetition tasks, we were able to draw conclusions about the regions of the brain involved in phonological working memory.

Results:

Voxels associated with statistically significant decreases in BOLD activity in speech-motor cortex during sentence repetition are strongly concentrated in supramarginal gyrus, angular gyrus, and posterior STG/STS. A similar but smaller cluster of significant voxels was observed in the VLAM analysis for word repetition. Lastly, we found that the supra-sylvian component of the dorsal stream is modulated by task complexity whereas the infra-sylvian component of the dorsal stream is not modulated by task complexity.

Conclusions:

This is the first investigation demonstrating modulation of activity in speech-motor cortex during repetition task as a function of damage to upstream language network sites. This VLAM study provides sensitive and specific evidence that lesions to structures in the dorsal stream modulate responses to repetition in speech-motor cortex.