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This abstract addresses the question of human imitation through convergent evidence from neuroscience. We look at deficits in imitation following brain lesion, such as apraxia. We believe that looking at how imitation is impaired can unveil its underlying principles. We also take inspiration from numerous brain imaging studies to ground the functional architecture and information flow of our model. In the end we will use findings from monkey brain neurophysiological studies to implement the details of our processing modules. We aim at developing a model of visuo-motor imitation using tools from neural networks and dynamical systems. The model should account for some of the behaviors observed in faulty imitation. At this stage we have implemented a somatotopically organized neural network with probabilistically impaired transfer of information that simulates lesions at the level of the parietal cortex (a brain center for sensorimotor integration). To validate the model against human motion experimental data, we conduct, in collaboration with the Geneva University Hospital (HUG), kinematic studies with brain damaged adults specifically disabled in gesture imitation. The model will motivate the realization of computer-based rehabilitation tools.

Poster presented at the ESF Research Conference on Brain Development and Cognition in Human Infants, Maratea (Italy)

Familial hemophagocytic lymphohistiocytosis (FHLH) is a rare, rapidly progressive disorder of early childhood characterized by uncontrolled activation of T cells and macrophages. Although perforin gene mutations have been described in a proportion of patients with FHLH, the genotype/phenotype correlation is still limited. Only a few patients with late onset clinical manifestations have been reported. The biochemical and immunologic alterations in the asymptomatic phase are not well known. We report on a family in which 2 fraternal twins both homozygous for a perforin mutation previously described as causative of the disease, markedly differed in phenotypic expression of FHLH. The twins also had a second novel heterozygous mutation. Natural killer (NK) activity was severely impaired in the patient and was normal in the asymptomatic fraternal twin. Our report highlights that FHLH may present after a long disease-free interval during which biochemical or immunologic alterations may be not evident, thus implying a role for interfering factors. (Blood. 2004;103:4610-4612)

Mutations of the IL2RG encoding the common γ-chain (γc) lead to the X-linked SCID disease. Gene correction through ex vivo retroviral transduction restored the immunological impairment in the most of treated patients, although lymphoproliferative events occurred in five of them. Even though in two cases it was clearly documented an insertional mutagenesis in LMO2, it is conceivable that γc could have a role per se in malignant lymphoproliferation. The γc is a shared cytokine receptor subunit, involved also in growth hormone (GH) receptor signaling. Through short interfering RNA or using X-linked SCID B lymphoblastoid cell lines lacking γc, we demonstrate that self-sufficient growth was strongly dependent on γc expression. Furthermore, a correlation between γc amount and the extent of constitutive activation of JAK3 was found. The reduction of γc protein expression also reduced GH-induced proliferation and STAT5 nuclear translocation in B lymphoblastoid cell lines. Hence, our data demonstrate that γc plays a remarkable role in either spontaneous or GH-induced cell cycle progression depending on the amount of protein expression, suggesting a potential role as enhancing cofactor in lymphoproliferation.