Neuropsychology and Neuroanatomy of Code Switching: Test Development and Application

Code switching has been studied in the context of a side effect of neurological pathology. However, little is known about how to apply code switching to the assessment of neuropathology and test development. This study reviewed and identified cognitive and linguistic theoretical underpinning, and neuropsychological and neuroanatomical aspects of code switching in order to use code switching to activate interference. These provide valuable information to consider for developing code switching-based neuropsychological tests. Overall, this study found that code switching is a diverse and multi-dimensional process. Theories mainly denote activation of the retrieval and organization of lexicolinguistic knowledge. Neuropsychological domains that are involved include executive functions, lexical retrieval, and working memory. Brain regions implicated in code switching heavily rely on frontosubcortical structures and, to a lesser extent, temporal and parietal cortical regions. These areas mainly involve executive control and language functions, which act to select relevant and inhibit irrelevant language networks. Specifically, these regions include the anterior cingulated cortex, the left dorsolateral prefrontal cortex, the bilateral supramarginal gyri, left caudate, left putamen, left globus pallidus, left thalamus, and middle temporal areas. The paper outlines the application of code switching tests using common executive functioning, lexical fluency, and working memory neuropsychology instrument. These include code switching versions of phonemic fluency, semantic fluency, written and oral Trail Making Test, and digit span. Interference, dual task, and other formulas are used to determine the degree of language interference and switching.