Recovery of offline and online sentence processing in aphasia: Language and domain-general network neuroplasticity

Abstract

This paper examined the effects of treatment on both offline and online sentence processing and associated neuroplasticity within sentence processing and dorsal attention networks in chronic stroke-induced agrammatic aphasia. Twenty-three neurotypical adults and 19 individuals with aphasia served as participants. Aphasic individuals were randomly assigned to receive a 12-week course of linguistically-based treatment of passive sentence production and comprehension (N = 14, treatment group) or to serve as control participants (N = 5, natural history group). Both aphasic groups performed two offline tasks at baseline and three months following (at post-testing) to assess production and comprehension of trained passive structures and untrained syntactically related and unrelated structures. The aphasic participants and a healthy age-matched group also performed an online eyetracking comprehension task and a picture-verification fMRI task, which were repeated at post-testing for the aphasic groups. Results showed that individuals in the treatment, but not in the natural history, group improved on production and comprehension of both trained structures and untrained syntactically related structures. Treatment also resulted in a shift toward more normal-like eye movements and a significant increase in neural activation from baseline to post-testing. Upregulation encompassed right hemisphere regions homologs of left hemisphere regions involved in both sentence processing and domain-general functions and was positively correlated with treatment gains, as measured by offline comprehension accuracy, and with changes in processing strategies during sentence comprehension, as measured by eyetracking. These findings provide compelling evidence in favor of the contribution of both networks within the right hemisphere to the restoration of normal-like sentence processing patterns in chronic aphasia.

Keywords: Aphasia; Eyetracking; Online sentence processing; Sentence comprehension; Treatment of underlying forms; fMRI.

Copyright © 2019 Elsevier Ltd. All rights reserved.

Figures

Fig. 1 –

Example pair of semantically reversible pictures used in treatment, probe tasks, and the comprehension fMRI task.

Fig. 2 –

Schematic representation of the fMRI protocol, for sentence (active, passive) trials (a) and control trials (b).

Fig. 3 –

Individual acquisition curves derived from the weekly probe tasks for a) production and b) comprehension of the trained items. Lines display the percentage of correct responses at BL (average of multiple baseline assessments) and at 4 time points over the course of treatment (i.e., every three weeks), for each participant.

Fig. 4 –

Mean percent accurate responses by sentence type, at baseline (BL) and post-testing (POST), for the two participant groups on the sentence production priming task (production). FP.u = full passives with adjunct (untrained items); UP = untrained passives, UAC = active unaccusatives, ACT = active transitives; OC = object clefts. Bars indicate mean standard error.

Fig. 5 –

Mean percent correct responses by sentence type, at baseline (BL) and post-testing (POST), for the two participant groups on the full probe picture verification task (comprehension). FP.u = full passives with adjunct (untrained items); UP = untrained passives, UAC = active unaccusatives, ACT = active transitives; OC = object clefts. Bars indicate mean standard error.

Fig. 6 –

Proportion of fixations to the target picture during online comprehension of correctly-answered passive sentences at baseline (BL) (black line) and post-testing (POST), for the two aphasic groups. Sentence regions: N1+Aux = subject noun + auxiliary; V = verb; N/PP2 = post-verbal noun or prepositional phrase; S End = sentence end.

Fig. 7 –

Clusters of suprathreshold activation (p < .001, uncorrected, k > 46) for the Passive > Control (red) and the Control > Passive (blue) contrasts, in the group of healthy participants. Color bars indicate activation intensity, with lighter shades indicating larger T-values (i.e., greater activation).

Fig. 8 –

Areas of left hemisphere lesion overlap across participants in the treatment (a) and natural history (b) groups are shown in shades of gray, with lighter shades indicating maximal overlap. Clusters of significant suprathreshold activation (p < .001, uncorrected, k > 37) for the (Passive > Control, POST > BL) contrast are shown in shades of red, with lighter shades corresponding to higher T-values, i.e., greater activation intensity. No significant activation was observed in the natural history group.

Fig. 9 –

Relation between increased (POST > BL) activation in the SPN and DAN networks and changes in the offline comprehension z-score. Asterisks indicate statistically significant comparisons.

Fig. 10 –

Relation between increased (POST > BL) activation in the SPN and DAN networks and changes in online thematic prediction (a, b) and online thematic integration (c, d). 9a shows a significant relation between upregulation in the right SPN and a decrease in the proportion of fixations to the target, reflecting a shift toward an Agent-first strategy during processing of passive sentences. 9d shows a significant relation between upregulation in the right DAN and an increase in target fixations from the verb region to the end of the sentence.