The level of electrotonic coupling in the inferior olive is extremely high, but its functional role in cerebellar motor control remains elusive. Here, we subjected mice that lack olivary coupling to paradigms that require learning-dependent timing. Cx36-deficient mice showed impaired timing of both locomotion and eye-blink responses that were conditioned to a tone. The latencies of their olivary spike activities in response to the unconditioned stimulus were significantly more variable than those in wild-types. Whole-cell recordings of olivary neurons in vivo showed that these differences in spike timing result at least in part from altered interactions with their subthreshold oscillations. These results, combined with analyses of olivary activities in computer simulations at both the cellular and systems level, suggest that electrotonic coupling among olivary neurons by gap junctions is essential for proper timing of their action potentials and thereby for learning-dependent timing in cerebellar motor control.

Background: Post-stroke cognitive impairment (PSCI) occurs in approximately half of ischemic stroke survivors. Infarct location is a potential determinant of PSCI, but a comprehensive map of strategic infarct locations is lacking. In this large-scale multicenter lesion-symptom mapping study, we aimed to identify infarct locations most strongly predictive of PSCI, and use this information to develop a prediction model. Methods:We harmonized individual patient data from twelve cohorts through the Meta-VCI-Map consortium. Patients with acute symptomatic infarcts on CT/MRI and cognitive assessment <1 year poststroke were eligible. PSCI was defined as impairment in ≥1 cognitive domains on neuropsychological assessment or impairment on the Montreal Cognitive Assessment. Voxel-based lesion-symptom mapping (VLSM) was used to calculate voxel-wise odds ratios for PSCI. For the prediction model, a "location impact score" on a five-point scale was derived from the VLSM results. Combined internal-external validation was performed using leave-one-cohort-out cross-validation for all twelve cohorts. Findings:In our combined sample of 2950 patients (age 67±12 years, 39% female), 44% had PSCI. We achieved almost complete lesion coverage of the brain in our analyses (87%). Infarcts in the left frontotemporal lobes, left thalamus, and right parietal lobe were strongly associated with PSCI (False Discovery Rate corrected q<0•01; voxel-wise odds ratios >20). These strategic regions were mapped onto a three-dimensional brain template to visualize PSCI risk per brain region. The location impact score showed good correspondence between predicted and observed risk across cohorts after adjusting for cohortspecific PSCI occurrence. Interpretation:This study provides the first comprehensive map of strategic infarct locations associated with risk of PSCI. A location impact score was derived from this map that robustly predicted PSCI across cohorts and can be applied by clinicians to identify individual patients at risk of PSCI.

Compensatory mechanisms after genetic manipulations have been documented extensively for the nervous system. In many cases, these mechanisms involve genetic regulation at the transcription or expression level of existing isoforms. We report a novel mechanism by which single neurons compensate for changes in network connectivity by retuning their intrinsic electrical properties. We demonstrate this mechanism in the inferior olive, in which widespread electrical coupling is mediated by abundant gap junctions formed by connexin 36 (Cx36). It has been shown in various mammals that this electrical coupling supports the generation of subthreshold oscillations, but recent work revealed that rhythmic activity is sustained in knock-outs of Cx36. Thus, these results raise the question of whether the olivary oscillations in Cx36 knock-outs simply reflect the status of wild-type neurons without gap junctions or the outcome of compensatory mechanisms. Here, we demonstrate that the absence of Cx36 results in thicker dendrites with gap-junction-like structures with an abnormally wide interneuronal gap that prevents electrotonic coupling. The mutant olivary neurons show unusual voltage-dependent oscillations and an increased excitability that is attributable to a combined decrease in leak conductance and an increase in voltagedependent calcium conductance. Using dynamic-clamp techniques, we demonstrated that these changes are sufficient to transform a wild-type neuron into a knock-out-like neuron. We conclude that the absence of Cx36 in the inferior olive is not compensated by the formation of other gap-junction channels but instead by changes in the cytological and electroresponsive properties of its neurons, such that the capability to produce rhythmic activity is maintained.