Event-related potential correlates of verbal and pictorial feature comparison in aphasics and controls

The role and use of event-related potentials in aphasia: A scoping review

Event-related potentials (ERPs) can provide important insights into underlying language processes in both unimpaired and neurologically impaired populations and may be particularly useful in aphasia. This scoping review was conducted to provide a comprehensive summary of how ERPs have been used with people with aphasia (PWA), with the goal of exploring the potential clinical application of ERPs in aphasia assessment and treatment. We identified 117 studies that met inclusionary criteria, reflecting six thematic domains of inquiry that relate to understanding both unimpaired and aphasic language processing and the use of ERPs with PWA. In these studies, a wide variety of ERP components were reported. Inconsistencies in reporting of participant characteristics and study protocols limit our ability to generalize beyond the individual studies and understand implications for clinical applicability. We discuss the potential roles of ERPs in aphasia management and make recommendations for further developing ERPs for clinical utility in PWA.

Language reorganization in aphasics: an electrical stimulation mapping investigation

OBJECTIVE

The purpose of this investigation was to determine whether clinical speech deficits after brain injury are associated with functional speech reorganization.

METHODS

Across an 18-year interval, 11 patients with mild-to-moderate speech deficits underwent language mapping as part of their treatment for intractable epilepsy. These "aphasics" were compared with 14 matched "control" patients with normal speech who also were undergoing epilepsy surgery. Neuroanatomic data were compared with quantitative language profiles and clinical variables.

RESULTS

Cortical lesions were evident near speech areas in all aphasia cases. As expected, aphasic and control patients were distinguished by quantitative language profiles. The groups were further distinguished by the anatomic distribution of their speech sites. A significantly greater proportion of frontal speech sites was found in patients with previous brain injury, consistent with frontal site recruitment. The degree of frontal recruitment varied as a function of patient age at the time of initial brain injury; earlier injuries were associated with greater recruitment. The overall number of speech sites remained the same after injury. Significant associations were found between the number of the speech sites, naming fluency, and the lesion proximity in the temporal lobe.

CONCLUSION

Language maps in aphasics demonstrated evidence for age-dependent functional recruitment in the frontal, but not temporal, lobe. The proximity of cortical lesions to temporal speech sites predicted the overall extent of temporal lobe speech representation and performance on naming fluency. These findings have implications for neurosurgical planning in patients with preoperative speech deficits.

ERP predictors of individual performance on a prospective temporal reproduction task

The present study aimed at investigating whether different aspects of performance on a prospective reproduction task with a standard duration of 2 s had different antecedents in the event-related potentials (ERPs) accompanying standard presentations and reproduced intervals. On each trial, first the standard duration was presented as an empty auditory interval. After a short delay, participants reproduced this interval by means of two button presses defining onset and offset of the reproduced interval. About 25 participants were divided into groups of poor and good time estimators, once based on the coefficient of variation of their reproduced durations, and once based on the absolute error score. Interestingly, for both performance measures differences between participants were accompanied by ERP differences during standard presentations rather than reproduction itself. While larger P300 amplitudes evoked by standard interval offset predicted good reproduction performance in terms of a small coefficient of variation, small absolute error scores were accompanied by larger fronto-central negative slow wave during standard presentations. The results suggest an important role of attention to both the critical events that delimit the to-be-estimated temporal intervals, and to the passing of time between these events.

Electrophysiological support for strategic processing of spatial sentences

The aims of the present EEG study were to distinguish between the various representation options of spatial sentences and to gain insight into the moment at which differences in the processing of spatial sentences arise. To examine the possible existence of different strategies, we used sentence-sentence and sentence-picture verification trials in mixed blocks, whereby the probability of a specific second stimulus was fixed within a block but varied between blocks. Brain activation (slow wave, 550-1100 ms after stimulus onset) linked to parsing spatial sentences (and not nonspatial sentences) occurred at parieto-occipital regions associated with mental image processing, and only when participants were expecting to compare verbal information to a picture. Therefore, this study provides neuroimaging evidence that different representational formats of spatial sentences arise almost directly when people are reading a spatial sentence.

Temporal dynamics of linguistic processes are reorganized in aphasics' cortex: an EEG mapping study

Brain lesions are known to elicit reorganization of function in representational cortex. Using linguistic function as an example, we show that (a) injury-related reorganization may also be observed in language-related cortex and (b) this reorganization not only appears in cortical space but also in the dynamic flow of activity. The present study investigated cortical reorganization in a group of 10 nonfluent aphasics who demonstrated partial recovery of linguistic functions. Compared with controls, linguistic functions were organized in an atypical manner, both in terms of spatial structures involved and in the time course of the linguistic processes, from word reading to late stages of word encoding in working memory. For this purpose, event-related potentials were recorded in a two-stimulus design comprising phonological and semantic tasks. Subjects were asked to judge whether two words, separated by a 2-s interval, rhymed (phonological task) or were semantically associated. During word reading of the phonological task, controls showed negativity/activation over occipital sites, whereas patients displayed negativity at left-medial orbitofrontal locations anterior to the common sites of lesion. During the subsequent 2-s interval associated with word encoding, the two groups showed a reversed pattern: significant left-right anterior asymmetry prevailed in controls, whereas lateralization was absent in patients. Aphasics displayed maximum positivity/inhibition over the left frontal regions, at the typical site of lesion. Compared with controls, patients exhibited significant disinhibition (decreased positivity) of right frontal areas and greater activation of left temporal sites. These results suggest that the concept of language plasticity should include, in addition to spatial aspects of linguistic reorganization, the reorganized temporal dynamics associated with recovery of impaired functions.