Cognitive neuroscience of aphasia recovery and therapy

It is slightly over 40 years since cognitive neuroscience arrived on the research stage. This novel field revolutionised our concepts regarding the neural basis of cognition, including the processes underlying normal language processing, their breakdown in neurological patients (including aphasia) and their amelioration in the course of recovery, and it has advanced our knowledge ever since. Initially, language and recovery were solely explained with respect to cognitive models of processing, which built the basis for the assessment of impaired and preserved language components, the prediction of language behaviours over time, and the planning of speech and language therapy. With more recent advances in neuroimaging techniques, explanations have become increasingly embedded within neuroscience frameworks.

However, even though brain science has immensely widened our understanding of aphasia and its recovery beyond the purely cognitive view, by itself it cannot comprehensibly explain the respective phenomena and still relies on behavioural data and cognitive terms. Indeed, it seems likely that a partnership between cognitive and brain sciences will always be needed. The same holds for therapy-induced recovery in aphasia, which is the specific focus of this Special Issue. The ultimate neuroscience model of aphasia therapy will need to encapsulate a variety of mechanisms and factors. These will include the influence of individual patient characteristics, the operation of recovery mechanisms, basic learning principles, the influence of strategies, as well as factors relating to the method, target, and intensity of speech and language therapy. In a recent review on functional imaging studies, Crinion and Leff (2015) concluded that the greatest potential for progress lies within the consideration of questions regarding the complex neural network architecture that subserves both language and cognitive processes.

In concert with a better understanding of the mechanisms underlying recovery and therapy, future insights might offer the opportunity to identify the individual behavioural and brain characteristics that are indicative of the course of recovery and predictive of the response to therapy. This combination would allow neuroscience data to explain impairments and therapy effects, and it would also inform individual speech and language therapy, thereby guiding interventions and enhancing patient benefit. Despite considerable success, many questions still await further examination before these goals are reached, and the papers presented in this Special Issue address some of the crucial and unresolved open issues in the cognitive neuroscience of aphasia recovery and therapy.

For the Special Issue, we welcomed a variety of neuroimaging techniques (functional and structural imaging, neuro-stimulation methods), study designs (single case or group studies), explanatory approaches (e.g., more cognitively or neuroscientifically driven, but with both being involved), therapy approaches (e.g., melodic intonation therapy (MIT)) and experimental tasks (e.g., naming and reading), data analyses (mapping of brain areas and connectivities), as well as aphasic symptoms (e.g., echolalia) – as long as they covered the cognitive neuroscience of both recovery and therapy on the highest levels of quality and novelty. Accordingly, the papers enhance our understanding of the interplay between behavioural and neural factors underlying aphasia, mechanisms of recovery, and the modulatory effect of therapy including neuro-stimulation.

The Special Issue comprises one overview and four original papers on the cognitive neuroscience of aphasia recovery and therapy. In line with the suggestions made by Crinion and Leff (2015), Ulm and colleagues (2018) first give an illustrative review of the systems neuroscience approach, which describes how contemporary neuroscience techniques can explore the complex interactions within the neural network and the resultant language functions. They focus on functional and structural magnetic resonance imaging, connectivity analyses, and neuro-stimulation methods, which also accord with the breadth of techniques utilised across the original papers in this Special Issue.

Berthier and colleagues (2018) present impressive data collected from a person with mitigated echolalia, a little understood symptom in aphasia which is defined by apparently deliberate and immediate repetition of heard words. Based on converging evidence from connectivity and behavioural analyses in a therapy study, they conclude that the symptom can be modulated by pharmacological and behavioural means, the presentation is related to an impaired meaning access, combined with a deficit in working memory and cognitive control, and echolalia is subserved by preserved activity of the dorsal in compensation of the impaired ventral language stream.

In their multiple-case study, Van de Sandt-Koenderman and colleagues (2018) investigated the behavioural and neural effects of MIT, an approach which is supposed to enable a laterality shift to the right hemisphere to compensate for the left-hemisphere damage in non-fluent aphasia. However, functional imaging and laterality index analyses for the nine participants revealed that there was no consistent change of language lateralisation, with variation also being related to time post stroke: the post-acute participants tended to present a right-ward shift, whilst the chronic participants a left-ward shift. Such data are consistent with the hypothesis that there are contrastive neural responses dependent on the phase of recovery (cf. Price & Crinion, 2005; Saur et al., 2006).

Long and colleagues (2018) report functional imaging data for two different tasks, naming and repetition, in five participants with stroke affecting the posterior cerebral artery at three time points from the subacute to the chronic phase of recovery. The brain responses varied in relation to both task and recovery phase, revealing the importance of appropriate compilation of tasks and of task choice for neurally guided therapy, such as non-invasive brain stimulation. As observed by Van de Sandt-Koenderman and colleagues and despite expectations, Long et al. found some decrease of performance over time if patients were not treated.

Sandars and colleagues (2018) used non-invasive brain stimulation, namely transcranial direct current stimulation (tDCS), in a participant with chronic non-fluent aphasia. Anomia treatment which was supplemented by anodal tDCS to perilesional frontal regions in the left frontal lobe was more effective—as measured by naming accuracy—than the behavioural naming therapy alone.

We hope that you enjoy reading the contributions to the current Special Issue on the Neuroscience of Aphasia Recovery and Therapy, and feel both well-informed and inspired by them.

Disclosure statement

No potential conflict of interest was reported by the authors.