1. Orienting network dysfunction in progressive multiple sclerosis (ID 208) Chalah MA 1,2, Palm U 1,3, Nguyen R 1,4, Créange A 1,4, Lefaucheur JP 1,2, Ayache SS 1,2 1 EA 4391, Excitabilité Nerveuse et Thérapeutique, Université Paris-Est-Créteil, France 2 Service de Physiologie – Explorations Fonctionnelles, Hôpital Henri Mondor, Assistance Publique – Hôpitaux de Paris, Créteil, France 3 Department of Psychiatry, Psychotherapy and Psychosomatics, Ludwig-Maximilian University, Germany 4 Service de Neurologie, Hôpital Henri Mondor, Assistance Publique – Hôpitaux de Paris, Créteil, France Background / Objective  Cognitive impairment affects up to 70 % of multiple sclerosis (MS) patients; the most frequently impaired domains being memory, processing speed and attention. In progressive MS subtypes, the increase in lesion load and cerebral atrophy throughout disease progression might have more impact on the attentional capacities.  The Attention Network Test (ANT) is a validated tool to assess the three main attentional networks: alerting network that controls vigilance, orienting network in charge of orientation to external stimuli, and executive function network that deals with solving conflict.  Our objective was to assess the attentional networks in progressive MS using ANT (figures 1 and 2). Methods  25 patients with primary (n = 10) or secondary (n=15) progressive MS and 25 age and sex matched healthy subjects were enrolled. All participants were right-handed. For the patients group, the following inclusion criteria were used: (i) definite diagnosis of progressive MS according to the revised 2010 McDonald criteria, (ii) stable treatment since at least one month, (iii) absence of comorbid neurologic or psychiatric disorders, particularly depression defined as Beck Depression Inventory score >19, (iv) absence of severe upper limb impairment and (v) absence of visual acuity or field deficits.  The cognitive screening and attention evaluation were performed in all participants using the Symbol Digit Modality Test (SDMT) and ANT respectively.. Results  Regarding ANT parameters, MS patients were slower and less accurate than their healthy counterparts; and were found to have a significative deficit in the orienting network.  ANT parameters were positively correlated with the disability scores and the progressive phase duration.  Concerning SDMT, MS patients scored less than the healthy subjects Vázquez-Marrufo, M. et al., 2014. Neural correlates of alerting and orienting impairment in multiple sclerosis patients. PLoS One. 12;9:e97226. Fan, J.et al., 2002. Testing the efficiency and independence of attentional networks. J. Cogn. Neurosci.14, 340-347. References Figure 2 Conclusion  Our study was the first to report an exclusive dysfunction in the orienting network of attention in progressive MS; such a finding might be attributed to the higher number of cortical lesions reported in progressive MS compared to the relapsing remitting forms.  Our study further supports the value of ANT and SMDT in evaluating different aspects of cognitive impairment in MS patients, and emphasizes the alteration of the orienting attentional network in MS patients with progressive subtypes. Figure 1