Hemodynamic Responses in the Left Temporal Region During Japanese Reading: Differences Between Task Conditions and Associations with Reading-Related Cognitive Abilities

This study aimed to investigate left temporal lobe activity during Japanese reading by examining both task-dependent activity and activity associated with individual differences in reading-related cognitive abilities. Using functional near-infrared spectroscopy (fNIRS), we measured hemodynamic responses around the left temporal lobe during oral reading of words and nonwords in 27 adult female Japanese university students. Furthermore, the relationships of these responses with word rapid reading, Rapid Automatized Naming (RAN), and digit span tasks were analyzed. Uncorrected analysis revealed significant differences between the nonword and word conditions in oxygenated hemoglobin at Channel 12 and deoxygenated hemoglobin at Channel 9; however, these differences did not maintain statistical significance after False Discovery Rate (FDR) correction across the 17 channels. In contrast, activity at Channel 9 was correlated with the time required for word rapid reading and RAN, as well as performance on forward and backward digit span tasks, and these correlations remained significant even after FDR correction. In conclusion, while the extent to which task-dependent phonological decoding load is reflected in left temporal lobe activity warrants further verification, our findings suggest that hemodynamic responses around the left temporal lobe are associated with individual differences in reading speed, naming speed, and phonological short-term/working memory. These findings provide insights by comprehensively capturing neural activity during Japanese reading from the dual perspectives of task-dependent and individual difference-related activities.