A Systematic Review of Native Languages Mapped With Direct Electrical Stimulation During Awake Craniotomy

Human language exhibits both universal characteristics and remarkable diversity. While neuroimaging has identified a shared fronto-temporo-parietal network across languages, causal inferences require techniques such as direct electrical stimulation (DES), which is performed during awake craniotomy. However, it is unclear which native languages have been mapped using DES. We conducted an analysis of which native languages were mapped in monolingual patients undergoing DES during awake craniotomy. Data was extracted from an open-access systematic review dataset of language errors from patients during awake craniotomy. An additional literature review and author communication were performed to identify the language type. Descriptive statistics and chi-squared analysis were used. The analysis identified 893 stimulation sites across 73 studies, involving nine languages: French, English, Chinese, Japanese, Italian, Dutch, Spanish, German, and Persian. These languages represent 27.2% of native languages spoken globally. The predominant mapped language family was Indo-European (670 stimulation sites; 75%), followed by Sino-Tibetan (186 stimulation sites; 20.8%) and Japonic (37 stimulation sites; 4.1%). There was a significant difference between the frequencies of the total number of global native speakers and stimulation sites (x² = 2071.33, df = 28, p <0.00001). We calculated a 'stimulation site per million native speakers' metric and identified that the top mapped languages per population size were French (4.62), Dutch (0.99), and English (0.65). This study underscores a significant bias in DES-based language mapping literature, with under-representation of languages spoken by most of the global population. Standardized, multi-language testing paradigms are crucial for addressing these disparities and advancing inclusive cognitive neuroscience.