Neuroplasticity of language networks in aphasia: advances, updates, and future challenges

Researchers have sought to understand how language is processed in the brain, how brain damage affects language abilities, and what can be expected during the recovery period since the early 19th century. In this review, we first discuss mechanisms of damage and plasticity in the post-stroke brain, both in the acute and the chronic phase of recovery. We then review factors that are associated with recovery. First, we review organism intrinsic variables such as age, lesion volume and location and structural integrity that influence language recovery. Next, we review organism extrinsic factors such as treatment that influence language recovery. Here, we discuss recent advances in our understanding of language recovery and highlight recent work that emphasizes a network perspective of language recovery. Finally, we propose our interpretation of the principles of neuroplasticity, originally proposed by Kleim and Jones (1) in the context of extant literature in aphasia recovery and rehabilitation. Ultimately, we encourage researchers to propose sophisticated intervention studies that bring us closer to the goal of providing precision treatment for patients with aphasia and a better understanding of the neural mechanisms that underlie successful neuroplasticity.P50 DC012283 - NIDCD NIH HHSPublished versio

Neural connectivity in syntactic movement processing

Linguistic theory suggests non-canonical sentences subvert the dominant agent-verb-theme order in English via displacement of sentence constituents to argument (NP-movement) or non-argument positions (wh-movement). Both processes have been associated with the left inferior frontal gyrus and posterior superior temporal gyrus, but differences in neural activity and connectivity between movement types have not been investigated. In the current study, functional magnetic resonance imaging data were acquired from 21 adult participants during an auditory sentence-picture verification task using passive and active sentences contrasted to isolate NP-movement, and object- and subject-cleft sentences contrasted to isolate wh-movement. Then, functional magnetic resonance imaging data from regions common to both movement types were entered into a dynamic causal modeling analysis to examine effective connectivity for wh-movement and NP-movement. Results showed greater left inferior frontal gyrus activation for Wh > NP-movement, but no activation for NP > Wh-movement. Both types of movement elicited activity in the opercular part of the left inferior frontal gyrus, left posterior superior temporal gyrus, and left medial superior frontal gyrus. The dynamic causal modeling analyses indicated that neither movement type significantly modulated the connection from the left inferior frontal gyrus to the left posterior superior temporal gyrus, nor vice-versa, suggesting no connectivity differences between wh- and NP-movement. These findings support the idea that increased complexity of wh-structures, compared to sentences with NP-movement, requires greater engagement of cognitive resources via increased neural activity in the left inferior frontal gyrus, but both movement types engage similar neural networks.This work was supported by the NIH-NIDCD, Clinical Research Center Grant, P50DC012283 (PI: CT), and the Graduate Research Grant and School of Communication Graduate Ignition Grant from Northwestern University (awarded to EE). (P50DC012283 - NIH-NIDCD, Clinical Research Center Grant; Graduate Research Grant and School of Communication Graduate Ignition Grant from Northwestern University)Published versio

Implicit and Explicit Learning in Aphasia

Implicit learning is an incidental, inductive learning process that occurs without the use of explicit strategies. To date, few studies have investigated implicit learning subsequent to stroke, and almost all have used visuomotor tasks (e.g., Boyd & Winstein, 2004; 2006; Exner, Weniger, & Irle, 2001; Gomez-Beldarrain, Garcia-Monco, Rubio, & Pascual-Leone, 1998; Orrell, Eves, Masters, & MacMahon, 2007). The present study used a Serial Search Task developed by Goschke and colleagues (2001) to examine implicit and explicit learning of an auditory word sequence in individuals with stroke-induced agrammatic aphasia and healthy age-matched adults. The present study also included a listening sentence span task to evaluate working memory. Research indicates that many aphasic individuals have working memory impairments, which are highly interrelated with language comprehension and overall aphasia severity (Caspari, Parkinson, LaPointe, & Katz, 1998; Friedmann & Gvion, 2003; Sung et al., 2009; Wright & Shisler, 2005). However, little is known about how working memory deficits relate to learning in aphasia

Statistical Learning in Aphasia: Preliminary Results from an Artificial Grammar Learning Task

Statistical learning, i.e., the discovery of structure based on statistical properties of stimuli, is considered an implicit process that plays an important role in nonlinguistic and linguistic tasks, including speech segmentation and grammar learning (Aslin & Newport, 2012; Saffran, 2002; Saffran et al., 1996). Moreover, individual differences in statistical learning ability have been shown to be associated with natural language processing (Misyak & Christiansen, 2012; Misyak et al., 2010). Yet little is known about this type of learning in individuals with aphasia, who must relearn linguistic skills after brain damage. To date, studies of implicit learning processes in aphasia have provided mixed results, including evidence of limited or absent implicit learning for a visual artificial grammar (Christiansen et al., 2010; Zimmerer et al., 2014), as well as evidence of relatively intact implicit learning in Serial Reaction Time tasks (Goschke et al., 2001; Schuchard & Thompson, 2013). The purpose of the present study was to test statistical learning and overnight consolidation of an artificial phrase structure grammar under implicit conditions in individuals with agrammatic aphasia and healthy age-matched adults

Noun and verb naming: Phonological facilitation effects on naming latencies and viewing times in agrammatic vs. anomic aphasia

Phonological facilitation effects during noun and verb naming were examined in groups of agrammatic and anomic aphasic individuals and healthy controls. Phonologically related vs. unrelated auditory primes were presented simultaneously with target pictures to be named while naming latencies and eye-fixations (viewing times) were measured. Controls showed reduced naming latencies and viewing times following phonologically related, compared to unrelated, primes for both nouns and verbs. Agrammatic participants showed phonological facilitation for verb, but not noun naming; whereas, anomic participants showed the opposite pattern, suggesting phonological facilitation effects interact with differential lexical deficits in aphasia

Analyzing agrammatic narrative production using Northwestern Narrative Language Analysis (NNLA) and Computerized Language Analysis (CLAN): A qualitative and quantitative comparison

Spontaneous language sample analysis is often used to characterize production deficit patterns in aphasia. Methods for accomplishing this, however, are labor-intensive. The Computerized Language Analysis (CLAN) system, developed for analyzing children’s language production, has recently been adopted for analysis of aphasic speech samples through AphasiaBank. However, the extent to which this automated system accurately quantifies lexical and morophosyntactic deficits, commonly seen in agrammatism, has not been explored. This study compared the CLAN with the Northwestern Narrative Language Analysis (NNLA) system, developed to evaluate linguistic deficits in aphasia. Results indicate that the CLAN does not identify important characteristics of agrammatic production. (100

Neuroplasticity of Language Networks in Aphasia: Advances, Updates, and Future Challenges

Researchers have sought to understand how language is processed in the brain, how brain damage affects language abilities, and what can be expected during the recovery period since the early 19th century. In this review, we first discuss mechanisms of damage and plasticity in the post-stroke brain, both in the acute and the chronic phase of recovery. We then review factors that are associated with recovery. First, we review organism intrinsic variables such as age, lesion volume and location and structural integrity that influence language recovery. Next, we review organism extrinsic factors such as treatment that influence language recovery. Here, we discuss recent advances in our understanding of language recovery and highlight recent work that emphasizes a network perspective of language recovery. Finally, we propose our interpretation of the principles of neuroplasticity, originally proposed by Kleim and Jones (1) in the context of extant literature in aphasia recovery and rehabilitation. Ultimately, we encourage researchers to propose sophisticated intervention studies that bring us closer to the goal of providing precision treatment for patients with aphasia and a better understanding of the neural mechanisms that underlie successful neuroplasticity

Time course of grammatical encoding in agrammatism

Two on-line sentence production experiments explored the time course of grammatical encoding in normal and agrammatic speakers. Incremental models suggest grammatical encoding proceeds in a word-by-word manner, without advanced planning. Structural models suggest a hierarchical predicate structure (e.g., verb argument structure, VAS) is encoded prior to speech onset. Results showed that when agrammatic speakers produced sentences in a pre-defined order, they produced sentences incrementally, similar to controls. However, in a free sentence production task, both controls and agrammatic speakers encoded VAS prior to speech onset. Further, agrammatic speakers’ syntactic deficits resulted in a greater use of VAS than controls

Electrophysiological responses to argument structure violations in healthy adults and individuals with nonfluent aphasia

Agrammatic individuals show impaired production of verbs with complex argument structure. Whether these participants show argument structure deficits during comprehension, however, is unclear. The present study investigated this issue by examining electrophysiological responses to argument structure violations in agrammatic individuals and healthy adults. Results showed that unlike control participants, who evinced a negative effect followed by a positive shift (N400-P600) in response to argument structure violations, individuals with agrammatic aphasia showed a P600 response only. This suggests impaired real time processing of the thematic requirements of verbs

The functional relation between syntactic and morphological recovery in aphasia: A case study

Morphological and syntactic impairments often co-occur in aphasia. Whether they are causally related is an issue of long-standing debate. This paper reports a case study of one individual with such impairments and describes their recovery in response to linguistically-motivated treatment. CL is a 56 year-old male with Broca's aphasia and limited capacity to produce syntactically complex utterances or grammatical morphology. He was enrolled in the Treatment of Underlying Forms protocol (Thompson, 2001). CL acquired production of Wh- questions, indicating improved access to CP, but his production of CP-related morphology declined. These patterns indicate that the recovery of syntactic and morphological processes in aphasia are at least partially independent