Lesion-symptom mapping reveals differential relationships between language and precise versus approximate numeracy

Numeracy, the foundation of mathematical processing, can be divided into two subcategories: approximate (quantity estimation) and precise numeracy (exact quantity). Loss of numeracy is commonly comorbid with aphasia following stroke, yet little is known about the neural basis of this relationship. We employed a support vector regression lesion-symptom mapping (SVR-LSM) analysis with N = 104 left hemisphere chronic stroke survivors to investigate the neural relationship between approximate and precise numeracy with language ability. Our results highlight key differences between how approximate and precise numeracy overlap with language processing regions. Approximate numeracy does not show a significant relationship to aphasia or language related regions, while precise numeracy shares considerable neural overlap with language areas and co-varies significantly with aphasia severity. The results support a priori hypotheses that the intraparietal sulcus (IPS) is crucially involved in approximation and additionally implicate regions including angular gyrus (AG), precentral gyrus, and anterior fusiform gyrus. In contrast, precise numeracy was linked to damage to the inferior frontal gyrus (IFG), AG, and anterior temporal cortex, as well as the caudate nucleus, thalamus, and posterior temporal regions. Overall, we provide evidence of strong lesion-deficit associations demonstrating distinct neural patterns between precise and approximate numeracy impairments. Crucially, we demonstrate that these subcategories have contrasting relationships with language processing.