## 5 Role of Cerebellum in the Ontogenesis of APA Control  
Taking into account the rich connections between the cerebellum and several regions of the cerebral cortex involved in motor control, posture, locomotion, and cognitive/emotional processes, aberrant cerebellar growth might have significant consequences on the functional organization of the cerebral cortex [73; 74]. In fact, the cerebellum supports the optimization of behavior, especially in procedural learning and skill acquisition. Therefore, an early damage of the cerebellum may induce significant changes in the structure and function of cerebro-cerebellar systems, with long-term effects on motor behavior.  
Ontogenesis of posture starts from infants (0-6 months) [75; 76; 77] and toddlers (6-18 months) [78; 79; 80]. In particular, the postural activities in sitting and reaching movements have been observed as early as three months, but only from six months do infants develop the ability to adapt postural activity to the specific mechanical situation [81]. Interestingly, three months and six months are the ages in which an increasing functional activity is detected in specific cerebral areas such as the cerebellum, basal ganglia, and frontal cortices [82; 83]. The development of APAs starts later (13-14 months) [81], and is related to the development of independent walking [78; 80]. During growth, other functional tasks were studied to detect APAs, such as load lifting and release [84; 85], upright stance without support [86], rising arms during standing [87], and gait initiation [88; 89]. From these works, it emerges that the feedforward control of posture is present but still immature at the age of 4-5 and it approaches that of adults only at 8 years of age [90]. However, the neural network for APA control seems to complete its maturation only after the age of 11 [91].  
Despite the importance of the cerebellum during the developmental stages, there is poor literature regarding APAs in children with cerebellar deficit. Lesions of the cerebellum lead to posture and muscle tone disorders. Particularly in early development, cerebellar deficits produce long-term alterations which underlay the potential contribution of this structure also to atypical development [74]. In this context, we analyzed quiet stance and gait initiation parameters in children affected by Pediatric Cerebellar Atakia (PCA) and compared them to those measured in healthy children [92]. PCAs are a heterogeneous group of cerebellar developmental disorders characterized by dysfunctional motor coordination and very early cerebellar symptoms. Static posturography highlighted alterations in cerebellar children, while the spatial and temporal parameters of APAs during gait initiation were not notably disturbed by the pathology. First step length and velocity were instead different between the groups. From a descriptive analysis of electromyographic recordings, cerebellar patients showed more alterations in the timing distribution of the muscular actions with respect to healthy controls, while the muscular pattern preceding the first step was preserved. The alteration in time delay between SOL inhibition and TA activation, in both stance and swing legs, agreed with literature that assigns to the cerebellum the involvement in feedforward muscle synergies [23; 64] and in the timing relationship among motor events [93; 94; 12; 95]. Therefore, this work supports the hypothesis that the cerebellum plays a key role also during human development, in particular, in building up internal models of gait initiation timings. Moreover, considering that the APA pattern was not affected by cerebellar dysfunction, pattern selection is a functional skill which may be attributed to other brain structures, like the basal ganglia [58].