Adaptation to a novel visuomotor transformation has revealed important principles regarding learning and memory. Computational and behavioral studies have suggested that acquisition and retention of a new visuomotor transformation are distinct processes. However, this dissociation has never been clearly shown. Here, participants made fast reaching movements while unexpectedly a 30-degree visuomotor transformation was introduced. During visuomotor adaptation, subjects received cerebellar, primary motor cortex (M1) or sham anodal transcranial direct current stimulation (tDCS), a noninvasive form of brain stimulation known to increase excitability. We found that cerebellar tDCS caused faster adaptation to the visuomotor transformation, as shown by a rapid reduction of movement errors. These findings were not present with similar modulation of visual cortex excitability. In contrast, tDCS over M1 did not affect adaptation, but resulted in a marked increase in retention of the newly learnt visuomotor transformation. These results show a clear dissociation in the processes of acquisition and retention during adaptive motor learning and demonstrate that the cerebellum and primary motor cortex have distinct functional roles. Furthermore, they show that is possible to enhance cerebellar function using tDCS.

Purpose To report the intraoperative use of microscope-integrated optical coherence tomography (MIOCT) to enable visualization for Descemet’s stripping automated endothelial keratoplasty (DSAEK) in 2 patients with advanced bullous keratopathy. Methods Patient 1 was an 83-year-old female and Patient 2 was a 28-year-old male both with limited vision and significant pain from bullous keratopathy that underwent palliative DSAEK. Due to the severity and chronicity of the corneal decompensation in both patients, the view past the anterior cornea was negligible using standard microscope illumination techniques. We used spectral-domain (Patient 1) and swept-source (Patient 2) MIOCT, both of which rely on infrared illumination, to visualize key parts of the DSAEK procedure. Results Graft insertion, unfolding, tamponade, and attachment could be dynamically visualized intraoperatively despite the nearly opaque nature of the host corneas. Postoperatively, the grafts remained attached with significant corneal clearing, improvement in visual acuity, and pain relief for both patients. Conclusions MIOCT is a valuable tool for the corneal surgeon, allowing for DSAEK to be successfully performed even when the surgical microscope view is limited from severe corneal edema, as is often the case in patients with advanced bullous keratopathy. By using MIOCT, these patients can benefit from the advantages of DSAEK despite a clinically opaque cornea, which would otherwise be treated with a penetrating keratoplasty.