Non-fluent aphasia and neural reorganization after speech therapy: insights from human sleep electrophysiology and functional magnetic resonance imaging

Abstract

Stroke is associated with long-term functional deficits. Behavioral interventions are often effective in promoting functional recovery and plastic changes. Recent studies in normal subjects have shown that sleep, and particularly slow wave activity (SWA), is tied to local brain plasticity and may be used as a sensitive marker of local cortical reorganization after stroke. In a pilot study, we assessed the local changes induced by a single exposure to a therapeutic session of IMITATE (Intensive Mouth Imitation and Talking for Aphasia Therapeutic Effects), a behavioral therapy used for recovery in patients with post-stroke aphasia. In addition, we measured brain activity changes with functional magnetic resonance imaging (fMRI) in a language observation task before, during and after the full IMITATE rehabilitative program. Speech production improved both after a single exposure and the full therapy program as measured by the Western Aphasia Battery (WAB) Repetition subscale. We found that IMITATE induced reorganization in functionally-connected, speech-relevant areas in the left hemisphere. These preliminary results suggest that sleep hd-EEGs, and the topographical analysis of SWA parameters, are well suited to investigate brain plastic changes underpinning functional recovery in neurological disorders.

Figure 1

The normative unweighted model for the “observation” task (same for left and right hemispheres), with directional influences between endogenous variables (ROIs: M1: primary sensorimotor cortices; LPMCd: dorsolateral pre-motor cortex; LPMCv: lateral ventral premotor cortex; IP: inferior parietal lobule; postST: posterior superior temporal gyrus and sulcus; antST: anterior superior temporal gyrus and sulcus) shown with arrows. Error terms represented by “e” variables.

Figure 2

(top) Topographic distribution of power in the SWA range during the first 30 minutes of the first NREM sleep episode. Data collected at baseline (top-left) and after IMITATE speech therapy (top-right) on a single representative patient. Topographic features of SWA are highly reproducible across nights showing a right asymmetry due to the left hemispheric brain lesion. (bottom) Local effects of IMITATE on sleep SWA. Changes in sleep SWA after IMITATE measured as percentage difference from the baseline.

Figure 3

Time table of imaging sessions, IMITATE therapy sessions, and aphasia testing sessions, and results of comparison to normative model for one representative patient. Five time points (3 week intervals) of fMRI sessions are shown as T1-T5 plus follow-up session at 9 months post-therapy (TF). Behavioral aphasia testing sessions are indicated by red arrows, and the 7 therapy sessions are shown between T3 and T5. Results for comparison between the normative model and single patient at each time point in the left (LH) and right (RH) hemispheres are shown in the lower half of the figure. + indicates that the null hypothesis was accepted (p>0.05; no difference between predicted and observed models) at that time point.