Structural Brain Correlates of Digit-Span Performance in Adults: A Narrative Review of Evidence From Lesion and MRI Studies

The digit-span task is a widely used measure of working memory in clinical and research contexts. Although numerous studies have examined its neuroanatomical correlates, research findings are heterogeneous, and a clear synthesis of structural evidence is warranted. This review aimed to synthesise existing evidence linking structural integrity of brain regions (volume or lesion) with digit-span performance in adults, using findings from 23 peer-reviewed studies. Functional imaging studies, composite digit-span scores and paediatric/adolescent samples were excluded. PubMed search supplemented by citation tracking identified 23 eligible studies (17 lesion and six structural MRI) published until December 2025. Six regions were related to both forward and backward digit-span task performance (left inferior parietal, left insula, bilateral supplementary motor, bilateral cerebellum, left middle temporal and left thalamus regions). Forward span was uniquely associated with six left-hemisphere regions including the left superior temporal, caudate, putamen, superior frontal, inferior temporal and precuneus. Backward span was uniquely associated with the bilateral superior parietal, bilateral hippocampus, left sensorimotor, right precuneus and right posterior cingulate regions. Dorsolateral prefrontal and inferior frontal findings were mixed. Partially distinct neuroanatomical profiles between forward and backward digit-span tasks likely reflect differences between attentional control/storage demands and higher executive/manipulation demands, respectively. In conclusion, digit-span performance is related to a distributed neural network spanning cortical, subcortical and cerebellar regions. While forward and backward digit-span tasks share common substrates, distinct regions are also recruited, consistent with differing cognitive demands. These findings may inform clinical interpretation and targeted cognitive interventions for prevention and rehabilitation of working memory deficits.