Pathophysiology of language switching and mixing in an early bilingual child with subcortical aphasia

Abstract

Acquired aphasia after circumscribed vascular subcortical lesions has not been reported in bilingual children. We report clinical and neuroimaging findings in an early bilingual boy who incurred equally severe transcortical sensory aphasia in his first language (L1) and second language (L2) after a posterior left thalamic hemorrhage. Following recurrent bleeding of the lesion the aphasic symptoms substantially aggravated. Spontaneous pathological language switching and mixing were found in both languages. Remission of these phenomena was reflected on brain perfusion SPECT revealing improved perfusion in the left frontal lobe and left caudate nucleus. The parallelism between the evolution of language symptoms and the SPECT findings may demonstrate that a subcortical left frontal lobe circuity is crucially involved in language switching and mixing.

Executive and Language Control in the Multilingual Brain

“…Hence, although we may not totally rule out the possibility that each single lesion was responsible for different deficits (such as the frontal lesion for impaired executive functions and the parietal lesion for impaired language control or vice versa), it is more parsimonious to assume that the frontal lesion was responsible for both impairments. As to the crucial role of the left caudate-frontal lobe circuitry in language control, evidence provided by Mariën et al [14] shows remission of language mixing and switching is associated with increased perfusion of left frontal lobe and left caudate nucleus. Interestingly, in their bilingual case, perfusional deficits remained in left temporoparietal areas and the patient continued to display fluent aphasia in L1 and in L2.…”

“…As to the neural locus of the language control device, clinical case studies have shown that damage to a frontal-subcortical circuit not only leads to uncontrolled behavior in brain damaged individuals, but also pathological switching between languages and language mixing [12–14]. Functional neuroimaging studies with unimpaired multilingual speakers have corroborated such findings [15–17] showing that language switching relies on a prefrontal-caudate ACC (anterior cingulate cortex) circuit.…”

Pearls & Oy-sters: Selective postictal aphasia

“…10 This loop is the neuroanatomic device for language selection control, and functional neuroimaging demonstrates resolution of pathologic switching and mixing with functional restoration of this cortico-subcortical loop. 11 Both patients had structural lesions spanning the frontotemporal operculum with minor involvement of the white matter connecting the frontal lobe with the basal ganglia. Neither mixing nor switching was observed interictally or postictally.…”

Functional dissociation between Kana and Kanji: agraphia following a thalamic hemorrhage

“…Recently, a consensus is growing with regard to the explanatory power of the diaschisis hypothesis. Supporting evidence for this hypothesis was provided by several studies describing the depression of regional neuronal metabolism and cerebral blood flow in functionally connected brain regions [13][14][15].…”