Article
Functional Neuroanatomy of Semantic Aphasia
Abstract. There is currently a great need for modern, standardized neuropsychological tests for language assessment in Russian speakers with aphasia. Our group is working on the development of the Russian Aphasia Test (RAT). Within the scope of this work, two subtests for single-word comprehension of nouns and verbs were developed considering contemporary models of language processing and principles of psychometrics. The task for both subtests was spoken word-to-picture matching. The subtests were normed on individuals with aphasia (n = 45) and a control group (n = 30). This resulted in the final set of 30 diagnostic trials for nouns and verbs matched on relevant psychometric properties which are sensitive to language impairments for both fluent and non-fluent types of aphasia. This set of trials will be included in the final version of the RAT.
Language is viewed as one of the most lateralized human brain functions. Left hemisphere dominance for language has been consistently confirmed in clinical and experimental settings and constitutes one of the main axioms of neurology and neuroscience. However, functional neuroimaging studies are finding that the right hemisphere also plays a role in diverse language functions. Critically, the right hemisphere may also compensate for the loss or degradation of language functions following extensive stroke-induced damage to the left hemisphere. Here, we review studies that focus on our ability to choose words as we speak. Although fluidly performed in people with intact language, this process is routinely compromised in aphasic patients. We suggest that parceling word retrieval into its sub-processes – lexical activation and lexical selection – and examining which of these can be compensated for after left-hemisphere stroke can advance the understanding of the lateralization of word retrieval in speech production. In particular, the domain-general nature of the brain regions associated with each process may be a helpful indicator of the right hemisphere's propensity for compensation.
According to the theory of dynamic and systemic organization of higher cortical functions (Luria, 2002), spatial impairments show themselves not only in perception (visual or tactile), but also in understanding of certain sentence types – the so-called ’logical-grammatical constructions‘. Testing these constructions is traditionally included in the neuropsychological diagnosis of semantic aphasia (Tsvetkova et al., 1981). The aim of this study was to design and standardize an enhanced diagnostic test, which would allow to more precisely detect the severity and the character of speech disorders in patients with semantic aphasia.