Language processing from the perspective of electrical stimulation mapping

ABSTRACT

Electrical Stimulation (ES) is a neurostimulation technique that is used to localize language functions in the brain of people with intractable epilepsy and/or brain tumors. We reviewed 25 ES articles published between 1984 and 2018 and interpreted them from a cognitive neuropsychological perspective. Our aim was to highlight ES as a tool to further our understanding of cognitive models of language. We focused on associations and dissociations between cognitive functions within the framework of two non-neuroanatomically specified models of language. Also, we discussed parallels between the ES and the stroke literatures and showed how ES data can help us to generate hypotheses regarding how language is processed. A good understanding of cognitive models of language is essential to motivate task selection and to tailor surgical procedures, for example, by avoiding testing the same cognitive functions and understanding which functions may be more or less relevant to be tested during surgery.     

Augmentation of spelling therapy with transcranial direct current stimulation in primary progressive aphasia: Preliminary results and challenges

Background: Primary progressive aphasia (PPA) is a neurodegenerative disease that primarily affects language functions and often begins in the fifth or sixth decade of life. The devastating effects on work and family life call for the investigation of treatment alternatives. In this article, we present new data indicating that neuromodulatory treatment, using transcranial direct current stimulation (tDCS) combined with a spelling intervention, shows some promise for maintaining or even improving language, at least temporarily, in PPA.

Aims: The main aim of the present article is to determine whether tDCS plus spelling intervention is more effective than spelling intervention alone in treating written language in PPA. We also asked whether the effects of tDCS are sustained longer than the effects of spelling intervention alone.

Methods & Procedures: We present data from six PPA participants who underwent anodal tDCS or sham plus spelling intervention in a within-subject crossover design. Each stimulation condition lasted 3 weeks or a total of 15 sessions with a 2-month interval in between. Participants were evaluated on treatment tasks as well as on other language and cognitive tasks at 2-week and 2-month follow-up intervals after each stimulation condition.

Outcomes & Results: All participants showed improvement in spelling (with sham or tDCS). There was no difference in the treated items between the two conditions. There was, however, consistent and significant improvement for untrained items only in the tDCS plus spelling intervention condition. Furthermore, the improvement lasted longer in the tDCS plus spelling intervention condition compared to sham plus spelling intervention condition.

Conclusions: Neuromodulation with tDCS offers promise as a means of augmenting language therapy to improve written language function at least temporarily in PPA. The consistent finding of generalisation of treatment benefits to untreated items and the superior sustainability of treatment effects with tDCS justifies further investigations. However, the small sample size still requires caution in interpretation. Present interventions need to be optimised, and particular challenges, such as ways to account for the variable effect of degeneration in each individual, are discussed.     

'Anatomo-biological considerations on the centers of language': an Argentinian contribution to the 1906 Paris debate on aphasia

In 1906, the year of the renowned holistic–localizationist controversy between neurologists Pierre Marie and Jules Déjèrine in Paris, Christfried Jakob, a protagonist researcher of the cerebral cortex at the time working in Argentina, published two relevant articles entitled ‘Does Broca’s area exist?’ and ‘Anatomo-biological considerations on the centers of language’. The two articles addressed neuropsychological and developmental aspects of language functions in normality and pathology with regard to the brain areas that subserve them. The present article provides an English translation of Jakob’s second paper, on the embryonic and postnatal development of brain areas related to language. The information given and the views expressed may still shed, a century later, useful light on our understanding of brain–language relationships.     

A brief assessment of object semantics in primary progressive aphasia

Background: A cross-culturally valid nonverbal assessment of semantic knowledge is needed. Accurately identifying impairment of object semantics is important for diagnosis of several disorders, including distinguishing semantic variant primary progressive aphasia (svPPA), a neurodegenerative condition characterised by progressive impairment in word comprehension, from logopenic and nonfluent agrammatic variants, which are not associated with impaired object semantics. However, current assessments require culturally specific knowledge.

Aims: We developed a cross-culturally valid short form of the Pyramids and Palm Trees Test to assess object semantic memory. We investigated its clinical utility in differentiating the semantic variant of primary progressive aphasia, from the logopenic and nonfluent agrammatic variants. Areas of atrophy associated with poor performance were identified.

Methods & Procedures: Fourteen items that rely on knowledge of objects’ defining features were selected from the original 52-item version. The full and short forms were administered to healthy individuals in the US (N = 18), Argentina (N = 20), and Greece (N = 12) and performance was compared. Seventy-eight individuals with primary progressive aphasia in the US completed the short form. Behavioural performance of the svPPA group (N = 24) was compared to other variants. Atlas-based analysis identified regions where atrophy correlated with poor performance in 39 individuals with primary progressive aphasia who had high-resolution magnetic resonance imaging (MRI) scans.

Outcomes & Results: Control performance was classified as normal on the short form significantly more often than on the full version. Across groups with primary progressive aphasia, the group with semantic variant performed significantly worse than the groups with logopenic or nonfluent agrammatic variants. Volume in left anterior and inferior temporal cortex correlated with performance.

Conclusions: The short-form Pyramids and Palm Trees Test is a clinically relevant, cross-culturally valid assessment of nonverbal object semantics. It can be used to identify semantic impairments, with poor performance associated with atrophy of the temporal lobes.     

Patterns of brain reorganization subsequent to left fusiform damage: fMRI evidence from visual processing of words and pseudowords, faces and objects

Little is known about the neural reorganization that takes place subsequent to lesions that affect orthographic processing (reading and/or spelling). We report on an fMRI investigation of an individual with a left mid-fusiform resection that affected both reading and spelling (Tsapkini & Rapp, 2010). To investigate possible patterns of functional reorganization, we compared the behavioral and neural activation patterns of this individual with those of a group of control participants for the tasks of silent reading of words and pseudowords and the passive viewing of faces and objects, all tasks that typically recruit the inferior temporal lobes. This comparison was carried out with methods that included a novel application of Mahalanobis distance statistics, and revealed: (1) normal behavioral and neural responses for face and object processing, (2) evidence of neural reorganization bilaterally in the posterior fusiform that supported normal performance in pseudoword reading and which contributed to word reading (3) evidence of abnormal recruitment of the bilateral anterior temporal lobes indicating compensatory (albeit insufficient) recruitment of mechanisms for circumventing the word reading deficit.     

Expressive and receptive vocabulary in children with Williams and Down syndromes

Background Williams (WS) and Down syndromes (DS) are two genetic disorders that involve intellectual disability (ID) and have been extensively studied over the past decades because of the unique linguistic profiles they exhibit. Recent investigations seek to explore the fractionation of linguistic components within the cognitive system using genetically based neurodevelopmental disorders such as WS and DS and to identify different profiles of linguistic function in these two groups of individuals. Method The ‘expressive vocabulary’, ‘receptive vocabulary’, ‘word opposites’ and ‘word definitions’ subtests (Level 1) of the Test of Word Knowledge (TOWK) were used to assess lexical skills in six children with WS and five children with DS. Results Our findings indicate that the two syndromes exhibit substantial differences on linguistic tasks with individuals with WS performing at a higher level compared to those with DS and producing atypical responses in word definitions. The pattern of errors for each syndrome is qualitatively different suggesting that their underlying linguistic mechanisms are distinctive even though ID is similar. Conclusions This study supports the differential outcome of two chromosomal disorders with similar ID. It also argues in favour of the large within group variability of the two syndromes that is not related to mental age but rather to different underlying mechanisms supporting language. These findings are discussed in the light of the current evidence concerning linguistic knowledge of neurodevelopmental and genetic disorders.     

(Morpho)syntactic comprehension in agrammatic aphasia: Evidence from Greek

Background: A number of hypotheses have been formulated to account for comprehension data in agrammatic aphasia. They explain deficits in comprehending specific structures, such as semantically reversible non-canonical sentences, for example, Trace Deletion Hypothesis (TDH, Grodzinsky, 1986 Grodzinsky, Y. 1986. Language deficit and the theory of syntax. Brain and Language, 27: 135–159. doi:10.1016/0093-934X(86)90009-X[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 1990 Grodzinsky, Y. 1990. Theoretical perspectives on language deficits, Cambridge, MA: MIT Press. [Crossref] , [Google Scholar], 1995 Grodzinsky, Y. 1995. A restrictive theory of agrammatic comprehension. Brain and Language, 51: 26–51. doi:10.1006/brln.1995.1039[Crossref], [Web of Science ®] , [Google Scholar]), or functional categories, for example, Tree Pruning Hypothesis (TPH, e.g., Friedmann, 2006 Friedmann, N. 2006. Generalizations on variations in comprehension and production: A further source of variation and a possible account. Brain and Language, 96: 151–153. doi:10.1016/j.bandl.2005.06.002[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]); Tense Underspecification Hypothesis (TUH, Wenzlaff & Clahsen, 2004 Wenzlaff, M. and Clahsen, H. 2004. Tense and agreement in German agrammatism. Brain and Language, 89: 57–68. doi:10.1016/S0093-934X(03)00298-0[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 2005 Wenzlaff, M. and Clahsen, H. 2005. Finiteness and verb-second in German agrammatism. Brain and Language, 92: 33–44. doi:10.1016/j.bandl.2004.05.006[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]); Interpretable Features’ Impairment Hypothesis (IFIH; e.g., Varlokosta et al., 2006 Varlokosta, S., Valeonti, N., Kakavoulia, M., Lazaridou, M., Economou, A. and Protopapas, A. 2006. The breakdown of functional categories in Greek aphasia: Evidence from agreement, tense, and aspect. Aphasiology, 20: 723–743. doi:10.1080/02687030500513703[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). Several studies, however, report evidence contradicting these theories (e.g., Caramazza, Capasso, Capitani, & Miceli, 2005 Caramazza, A., Capasso, R., Capitani, E. and Miceli, G. 2005. Patterns of comprehension performance in agrammatic Broca's aphasia: A test of the Trace Deletion Hypothesis. Brain and Language, 94: 43–53. doi:10.1016/j.bandl.2004.11.006[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Dickey, Milman, & Thompson, 2008 Dickey, M. W., Milman, L. H. and Thompson, C. K. 2008. Judgment of functional morphology in agrammatic aphasia. Journal of Neurolinguistics, 21: 35–65. doi:10.1016/j.jneuroling.2007.08.001[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) and propose new accounts to explain the comprehension deficits in agrammatic aphasia, for example, Distributed Morphology Account (DMA, Dickey et al., 2008 Dickey, M. W., Milman, L. H. and Thompson, C. K. 2008. Judgment of functional morphology in agrammatic aphasia. Journal of Neurolinguistics, 21: 35–65. doi:10.1016/j.jneuroling.2007.08.001[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]).

Aims: Against the background above, this study investigates the ability of three Greek-speaking agrammatic individuals to comprehend a wide range of structures and functional categories: semantically reversible (canonical) active and (non-canonical) passive sentences, Complementizer Phrase, subject-verb Agreement, Tense, and Aspect.

Methods & Procedures: We administered: (a) two sentence-picture matching tasks to test comprehension of reversible active and passive sentences, and Tense; (b) a sentence grammaticality judgement task to test judgement of Tense, Aspect, and subject-verb Agreement; and (c) a picture-pointing task to test comprehension of Complementizer Phrase.

Outcomes & Results: (a) Two of the three agrammatic participants performed at chance on reversible passive sentences and above chance on active sentences. The third participant performed equally high on the two sentence types. Two participants performed at chance on Tense comprehension and one above chance. (b) The three participants were selectively or across-the-board impaired in judgement of Agreement, Tense, and Aspect. One of the two selectively affected participants had chance performance on Aspect and above chance performance on Agreement and Tense. The other one performed at chance on Aspect and Tense, and above chance on Agreement. The third participant's performance was equally poor on all three categories. (c) All three agrammatic participants performed above chance on the comprehension of Complementizer Phrase.

Conclusions: In comprehension/judgement, canonical and non-canonical sentences do not dissociate in all agrammatic speakers, while functional categories associated with the verb morphology may be compromised in the face of relatively well-preserved categories that are located higher in the syntactic hierarchy. All three agrammatic participants support the DMA, and two of them support the TDH. Instead, none of them provided support to the TPH, TUH, and IFIH.