Neural Mechanisms Underlying Learning following Semantic Mediation Treatment in a case of Phonologic Alexia

Abstract

Patients with phonologic alexia can be trained to read semantically impoverished words (e.g., functors) by pairing them with phonologically-related semantically rich words (e.g, nouns). What mechanisms underlie success in this cognitive re-training approach? Does the mechanism change if the skill is "overlearned", i.e., practiced beyond criterion? We utilized fMRI pre- and post-treatment, and after overlearning, to assess treatment-related functional reorganization in a patient with phonologic alexia, two years post left temporoparietal stroke. Pre-treatment, there were no statistically significant differences in activation profiles across the sets of words. Post-treatment, accuracy on the two trained sets improved. Compared with untrained words, reading trained words recruited larger and more significant clusters of activation in the right hemisphere, including right inferior frontal and inferior parietal cortex. Post-overlearning, with near normal performance on overlearned words, predominant activation shifted to left hemisphere regions, including perilesional activation in superior parietal lobe, when reading overlearned vs. untrained words.

Figures

Figure 1

Structural T1-weighted MRI scan for patient YCR (phonologic alexia, two years poststroke). Lesion was present in cortex and subjacent white matter in temporal and parietal lobes, including Wernicke’s area, posterior middle and superior temporal gyri, angular gyrus, supramarginal gyrus, and portions of inferior and superior parietal lobules.

Figure 2

YCR scores on experimental word lists (ITP=incorrect words to be trained and practiced (“overlearned”) with semantic mediation; ITU=incorrect words to be trained-but-not-practiced; IB=untrained incorrect words from baseline; CC=words consistently correct from baseline) and control condition (X=strings of letters or numbers) over time. Percent correct represent mean scores averaged over four runs per condition, except for during baseline testing. No audio recordings were available in the first run, therefore accuracy scores at baseline represent mean scores over three runs.

Figure 3

Semantic Mediation Treatment effect: BOLD signal increases observed during reading of trained and practiced (ITP) or trained but not practiced (ITU) vs. untrained (IB) words at three time points: a) pre-treatment (T1); b) post- classical treatment (T2); and c) post-overlearning (T3). Significant regions of activation shown superimposed on YCR’s reconstructed lateral and medial images at p

Figure 4

Overlearning effect: BOLD signal increases observed during reading of: a) trained and practiced (ITP) words vs. untrained (IB) words; b) ITP vs. trained but unpracticed words (ITU); c) ITP vs. words that were consistently correct from baseline (CC); and d) ITP vs. the control task. Significant regions of activation shown superimposed on YCR’s reconstructed lateral images at p

Figure 5

Lateralization Curves for gray matter for YCR in contrasts examining words (to be) trained and practiced vs. untrained words (ITP vs. IB) at three different time points: 1) T1 (blue: pre-treatment); 2) T2 (green: post-treatment with Semantic Mediation); and 3) T3 (red: post-extended practice [i.e., overlearning]). Curves produced using bootstrapping method (Wilke & Schmithorst, 2006) of examining lateralization over varying thresholds for the same contrasts. Numbers in parentheses indicate weighted means (WM).