Cerebellar Neuromodulation Impacts Reading Fluency in Young Adults.

The cerebellum is traditionally associated with the control of coordinated movement, but ample evidence suggests that the cerebellum also supports cognitive processing. Consistent with this, right-lateralized posterolateral cerebellar regions are engaged during a range of reading and reading-related tasks, but the specific role of the cerebellum during reading tasks is not clear. Based on the cerebellar contribution to automatizing movement, it has been hypothesized that the cerebellum is specifically involved in rapid, fluent reading. We aimed to determine whether the right posterolateral cerebellum is a specific modulator of reading fluency or whether cerebellar modulation is broader, also impacting reading accuracy, rapid automatized naming, and general processing speed. To do this, we examined the effect of transcranial direct current stimulation (tDCS) targeting the right posterolateral cerebellum (lobules VI/VII) on single-word reading fluency, reading accuracy, rapid automatized naming, and processing speed. Young adults with typical reading development ( = 25; 15 female sex assigned at birth, 10 male sex assigned at birth, aged 18-28 years [ = 19.92 ± 2.04 years]) completed the reading and cognitive measures after 20 min of 2 mA anodal (excitatory), cathodal (inhibitory), or sham tDCS in a within-subjects design. Linear mixed effects models indicated that cathodal tDCS decreased single-word reading fluency scores ( = -0.36, < 0.05) but did not significantly affect single-word reading accuracy, rapid automatized naming, or general processing speed measures. Our results suggest that the right posterolateral cerebellum is involved in reading fluency, consistent with a broader role of the cerebellum in fast, fluent cognition.