# Postural Control in Children with Cerebellar Ataxia
Considering the muscular actions that drive gait initiation, before the beginning of the imbalance phase, an inhibition occurs in the background EMG (electromyographic) activity of both SOL muscles, which are tonically active during quiet stance. SOL inhibitions are shortly followed by the recruitment of TA muscles, which are silent during quiet stance and activate close to the APA onset. In particular, in the stance leg, the SOL inhibition precedes TA excitation by about 100 ms [7]. A drop in the background activity is also observed in other dorsal muscles, like BF and ES, while bursts of activity occur in ventral muscles, like Rectus Femoris (RF) [14]. Less literature is available on APAs during gait initiation in children. A systematic survey by [PERSON] et al. (1998) [15] showed that APAs start developing at 2-3 years of age but complete their maturation well after the age of 8, a result in line with the observations carried out on toddlers up to 5 years old children [16] and in 4-6 years old children [17]. Another interesting study was published by [PERSON] et al. (2014) [18], who analyzed SOL and TA in \(10\pm 3\) years-old children and reported inhibition-excitation patterns like in adults, but with a lower time interval between SOL inhibition and TA excitation. Several studies showed altered gait initiation in those neurological diseases characterized by poor motor control, as Rett syndrome [18], Parkinson's disease [19], and cerebellar pathologies [20; 21]. In particular, [PERSON] and [PERSON] [21] reported that adults with cerebellar deficits showed a decreased force production and a significant reduction of the length and peak velocity of the first step, accompanied by impairments in the predictive adaptation of APAs to the mechanical needs of gait initiation. Despite these authors also found that the temporal parameters of APAs were overall preserved in patients with cerebellar disease, several other works [22; 23; 24; 25; 26] addressed the role of cerebellum in postural control and provided evidence that such structure is involved not only in modulating rate and force of muscle activities but also in determining their relative timing. Indeed, cerebellar deficits often lead to dysfunctional co-contractions [22; 24; 26]. In this regard, it is worth recalling the involvement of the cerebellum in building up the temporal pattern of APAs, in particular, its ability to create and store internal models of body mechanics. This is proved by the contribution of the cerebellum in modulating sensory-motor interactions and integrating feed-forward and feed-back modes [27]. The cerebellum is also known to play an important role in many developmental disorders [28]. Nevertheless, very little attention has been given to the linkage between the development of postural control and the maturation of such neural structure. Aiming to elucidate this topic, we explored quiet stance and gait initiation in children affected by Pediatric Cerebellar Atakia (PCA), used as a model of cerebellar dysfunction vs. a healthy control group of comparable age. PCAs are a heterogeneous group of cerebellar developmental disorders characterized by dysfunctional motor coordination and very early cerebellar symptoms. The first clinical signsare marked hypotonia, wobbling gait, dysmetria, dysarthria, and a significant developmental delay. Most children show also marked speech impairment and cognitive deficits. In some cases, the cerebellum degenerates with time, but so slowly that it becomes difficult to classify the disorder as progressive or not [29]. In this framework, we studied a group of children with generalized cerebellar atrophy and clinical evidence of slow progression during follow-up (SlowP). In other cases, the disease has a proven non-progressive course, as in Joubert syndrome, which is characterized by cerebellar hypoplasia limited to the vermis and peduncles [30]. Thus, we also considered the second group of children (non-progressive, NonP) affected by this kind of pathology.