Effects of cerebellar lesions on working memory interacting 2 with motor tasks of different complexities

38 We examined the influence of focal cerebellar lesions on working memory (n-back task), gait and on 39 the interaction between working memory and different gait tasks in a dual-task paradigm. 40 The analysis included 17 young patients with chronic focal lesions after cerebellar tumor resection 41 and 17 age-matched controls. Patients have shown mild to moderate ataxia. Lesion sites were 42 examined based on structural magnetic resonance imaging. N-back tasks were executed with different 43 levels of difficulty (n=1-4) during sitting (baseline), treadmill walking and treadmill tandem walking 44 (dual-task conditions). 45 Patients exhibited decreased n-back performance particularly at difficult n-back levels and in dual46 task conditions. 47 Voxel-based lesion-symptom mapping revealed that decreased baseline n-back performance was 48 associated with lesions of the posterolateral cerebellar hemisphere and the dentate nucleus. By 49 contrast, decreased n-back performance in dual-task conditions was more associated with motor50 related areas including dorsal portions of the dentate and the interposed nucleus suggesting a 51 prioritization of the motor task. 52 During baseline walking, increased gait variability was associated with lesions in medial and 53 intermediate regions, whereas for baseline tandem gait lesions in the posterolateral hemispheres and 54 the dentate nucleus became important. Posterolateral regions overlapped with regions related to 55 baseline n-back performance. Consistently, we observed increased tandem gait variability with 56 growing n-back difficulty in the dual task condition. These findings suggest that dual-task effects in 57 cerebellar patients are at least partially caused by a common involvement of posterolateral cerebellar 58 regions in working memory and complex motor tasks. 59 60