Abstract
Central alexia is an acquired reading disorder co-occurring with a generalized language deficit (aphasia). We tested the impact of a novel training app, 'iReadMore', and anodal transcranial direct current stimulation of the left inferior frontal gyrus, on word reading ability in central alexia. The trial was registered at www.clinicaltrials.gov (NCT02062619). Twenty-one chronic stroke patients with central alexia participated. A baseline-controlled, repeated-measures, crossover design was used. Participants completed two 4-week blocks of iReadMore training, one with anodal stimulation and one with sham stimulation (order counterbalanced between participants). Each block comprised 34 h of iReadMore training and 11 stimulation sessions. Outcome measures were assessed before, between and after the two blocks. The primary outcome measures were reading ability for trained and untrained words. Secondary outcome measures included semantic word matching, sentence reading, text reading and a self-report measure. iReadMore training resulted in an 8.7% improvement in reading accuracy for trained words (95% confidence interval 6.0 to 11.4; Cohen's d = 1.38) but did not generalize to untrained words. Reaction times also improved. Reading accuracy gains were still significant (but reduced) 3 months after training cessation. Anodal transcranial direct current stimulation (compared to sham), delivered concurrently with iReadMore, resulted in a 2.6% (95% confidence interval -0.1 to 5.3; d = 0.41) facilitation for reading accuracy, both for trained and untrained words. iReadMore also improved performance on the semantic word-matching test. There was a non-significant trend towards improved self-reported reading ability. However, no significant changes were seen at the sentence or text reading level. In summary, iReadMore training in post-stroke central alexia improved reading ability for trained words, with good maintenance of the therapy effect. Anodal stimulation resulted in a small facilitation (d = 0.41) of learning and also generalized to untrained items.10.1093/brain/awy138_video1awy138media15796149281001.
Highlights
Acquired disorders of reading may be a consequence of generalized language impairment
This study tested the efficacy of two concurrent therapies for central alexia: (i) iReadMore, a crossmodal, lexical word reading therapy; and (ii) anodal transcranial direct current stimulation (tDCS) delivered to left inferior frontal gyrus (LIFG)
Pretreatment reading of the high frequency, low imageability ‘core’ words was initially poor, but as a result of iReadMore training accuracy improved by 6% and reaction time improved by 210 ms
Summary
Acquired disorders of reading may be a consequence of generalized language impairment We refer to these disorders as central alexias (but see Ellis and Young, 1988; Warrington and Shallice, 1980, for a slightly different use of this term). According to the primary systems hypothesis and connectionist triangle model of reading (Plaut et al, 1996), central alexia may be due to damage to the phonological (P), semantic (S) or orthographic (O) system, or the connections between them (see Coltheart et al, 2001; Coltheart, 2006, for a different theory of reading and the causes of phonological and surface dyslexia). Damage affecting phonology or the direct O-P mappings primarily impairs pseudoword reading (phonological alexia; Patterson and Lambon-Ralph, 1999; Crisp and Lambon Ralph, 2006) and causes semantic errors in more severe cases (deep alexia; Crisp et al, 2011). Damage to the semantic system or the semantically (S) mediated O-S-P route impairs irregular word reading (surface alexia; Patterson and Lambon Ralph, 1999; Woollams et al, 2007)
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