Implications of Subcortical structures in Aphasia.

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Introduction Classical attempts to capture the nature of aphasia have been “corticocentric” in identifying language processes. Recent conceptual and technical advances force us to reconsider the neural bases of language. In this work we aim to review several studies of damaged subcortical structures (thalamus and basal ganglia) that show large effects in language performance. Different sources of evidence have shown the close relationship between damage to the thalamus, and the basal ganglia, and language deficits. The observation of acquired lesions such as cerebro-vascular accidents and traumatic brain injuries, degenerative processes such as dementia, and treatment studies for aphasia are starting to bring some insight into the contribution of these subcortical structures to the language network (Damasio et al., 1982; Weiller et al., 1993; Luzzatti et al., 2006). However, so far, scattered information and different methodological approaches make it difficult to build up a clear picture. After our exploration of the relationship between aphasia and lesion site when this affects the thalamus and the basal ganglia and the comparison of language profile of both damaged structures we found that the incidence of aphasia as a consequence of lesions affecting subcortical portions is similar to that of cortical insult. We feel that this has important consequences for both assessment and recovery. The review also exposes the need to add association tracts to the discussion. Methods The literature review conducted on PubMed and Medline included the key words ‘aphasia’ AND ‘lesion’ AND (‘thalamus’ OR ‘basal ganglia’). After a first search, which retrieved 159 results (80 on thalamus, 79 on basal ganglia), we applied the following inclusion criteria: articles referring to adult acquired aphasia (rather than congenital deficits) written in English. A total of 43 studies were finally included (18 referring to the thalamus, 25 to the basal ganglia). Two were literature reviews and 41 reported the results of either case or group studies in typologically different languages, including among others Chinese, Dutch, English, German, Japanese, Portuguese, Serbian, and Turkish. A final set of data of 682 individuals (288 with thalamus lesion and 394 with basal ganglia lesion) was classified according to the presence/absence of assessable language deficits. When possible, subcortical damage was further specified. Results Taken together, the results indicate that aphasia is a common outcome after a lesion to subcortical structures. Findings show that 110 out of 394 aphasic patients with lesion in the basal ganglia exhibited comprehension deficits, while 31 participants out of 288 with thalamic aphasia. Likewise, 129 aphasics of affected basal ganglia out of 394 had impaired naming, whereas 12 participants had impaired naming out of 288 individuals with thalamic aphasia. See figure 1. Figure 1: The percentage of language impairment in two sets of aphasic patients (the thalamus and the basal ganglia). Despite contradictory results and even cases of double dissociation (for an example of absence of language deficits in the event of thalamic lesions see Cappa et al., 1986), our literature review confirms the major role of subcortical structures in language processing.

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... Assume also that Agree/Search is implemented via cross-cortical evoked γ due to the role of this band in attention and perceptual ''feature binding'' (Bartos et al., 2007;Sohal et al., 2009) and the distributed nature of the inter-modular representations Agree/Search operates over (see Figure 2 for predictions about rhythmic disruptions for agreement relations). Overall, we find this model compatible with recent findings that damage to the basal ganglia and thalamus can lead to various forms of aphasia and other linguistic deficits (Alamri et al., 2015); in turn contributing to an emerging rejection of the classical Wernicke-Lichtheim-Geschwind approach to neurolinguistics (Hagoort, 2014). This is why we expect it to contribute as well to a better understanding of language deficits in ASD. ...
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The occurrence of aphasia or neglect was related to anatomo-structural (CT/MRI), functional [regional cerebral blood flow (rCBF)] and pathogenetic features [duration of middle cerebral artery (MCA) occlusion and degree of cortical leptomeningeal anastomoses] in 57 cases (26 with and 31 without aphasia or neglect) with strictly subcortical infarcts of one defined type, i.e. striatocapsular infarcts. No distinct pattern of language disturbances was found. Aphasic syndromes did not differ in the amount of involvement of the putamen, pallidum, head of caudate nucleus and white matter. Patients with aphasia or neglect had larger infarcts than those without. However, there was no specific involvement of the basal ganglia, the internal capsule or the deep white matter in patients with aphasia or neglect. Patients with aphasia or neglect had a significantly longer duration of MCA occlusion and mostly poor leptomeningeal collaterals. The cortical rCBF was significantly decreased in the cortical MCA territory in the patients with aphasia or neglect only. The rCBF remained low at follow-up after 1 year and corresponded to focal cortical atrophy on MRI, although neglect had subsided completely in all patients and aphasia had improved considerably in almost 75% of the cases. Aphasia or neglect after striatocapsular infarcts are most likely due to selective neuronal loss of the cerebral cortex due to prolonged MCA occlusion and insufficient collateral blood flow. Individual differences in recovery from aphasia after striatocapsular infarction can be explained in terms of the number of surviving cortical neurons.
Five right-handed patients suffering from a recent CT-assessed left posterior thalamic hemorrhage are reported. In all patients a standard language examination performed within one month after stroke onset did not reveal aphasic disturbances. While the present series argues for the role of intrathalamic lesion localization, a review of the literature suggests that lesion site per se does not always account for the presence or absence of aphasia in the individual case. The importance of reduced blood flow and metabolism in cortical areas which appear undamaged on CT scan is briefly discussed.
Atypical aphasia syndromes were associated with circumscribed nonhemorrhagic infarctions of the anterior limb of the internal capsule and of the striatum, in the dominant hemisphere. None of the several cases could be classified in terms of the classic cortical aphasia syndromes, nor did they correspond to the description of aphasia produced by hemorrhage in the thalamus or putamen. Control subjects without aphasia had lesions in the same structures of the nondominant hemisphere, or they had comparably circumscribed damage, which was located lateral or caudal to the previously indicated locus. The findings raise the question of participation of the dominant striatum, and of the connectional systems that course in the anterior limb of the internal capsule, in language processing.
This paper reports the results of several studies on the mechanisms underlying Verb-Noun (V-N) dissociation. The objectives of the studies were to ascertain the location of the lesions causing predominant V or N impairment and to shed light on the different mental representations of these word classes through analyses of the data from neuropsychological patients. With regard to lesion sites, results obtained through an anatomo-correlative study on 15 V-impaired and 5 N-impaired aphasic patients indicate that lesions causing predominant N impairment were mostly located in the middle and inferior left temporal area. Three alternative lesion sites were associated with a V deficit (left posterior temporo-parietal lesions; large left fronto-temporal perisylvian lesions; deep lesions of the insula and/or the basal ganglia). In contrast to the results obtained from several neuropsychological and neuroimaging studies, none of the V-impaired patients had an isolated frontal lesion. The second aim is to discuss grammatical class interaction with semantic factors such as actionality or imageability (said to be the real cause of V-N dissociation). The retrieval of Ns and Vs in a sentence context was tested on 16 V-impaired aphasic patients and the resulting data indicate that imageability interacts with the retrieval of Ns and Vs, but cannot completely account for their dissociation.
Presentation Type: Poster Topic: Student first author Citation Implications of Subcortical structures in Aphasia
  • Subcortical
  • Aphasia
  • Basal Thalamus
  • S Ganglia Alamri
  • E Zhang
  • C Theofanopoulou
  • G Castillo
  • E Shi
  • Pt Martins
Keywords: subcortical, Aphasia, Thalamus, Basal Ganglia, language deficit Conference: Academy of Aphasia 53rd Annual Meeting, Tucson, USA, 18 Oct-20 Oct, 2015. Presentation Type: Poster Topic: Student first author Citation: Alamri S, Zhang E, Theofanopoulou C, Castillo G, Shi E, Martins PT, Martínez Ferreiro S and Boeckx C (2015). Implications of Subcortical structures in Aphasia..