S62 Abstracts P.061 Diffusion tensor imaging as a biomarker for the discrimination of bipolar and unipolar depression L. Parenti ∗ , C. Cara, I. Bollettini, B. Vai, S. Poletti, F. Benedetti IRCCS San Raffaele Hospital, Psychiatry and Clinical Psy- chobiology Unit, Milan, Italy Background: Bipolar disorder (BD) is one of the 10 world- wide most debilitating illnesses. Notably, 60% of BD indi- viduals are initially misdiagnosed as affected by Major De- pressive Disorder (MDD). This leads to inadequate treatment with severe clinical consequences (i.e. increased suicidal rate) [1]. Therefore, the identification of reliable biomark- ers for differential diagnosis is crucial to improve effective treatments, preventing detrimental clinical outcomes. In- deed, despite depressive symptoms are similarly expressed, structural brain endophenotypes could differentiate the two disorders, reflecting distinct pathophysiologic processes. Al- terations in white matter (WM) have been consistently re- ported in BD and MDD by comparing these groups to healthy controls (HC). However, the biomarkers for distinguishing the disorders are still blurred: few previous study directly compared BD, MDD and HC using tract-based spatial statis- tics (TBSS) [2]. The aim of this study is to characterized specific alterations of WM integrity differentiating BD from MDD depression, and HC, giving novel insight for possible illnesses endophenotypes. Methods: Seventy-nine currently depressed patients suffer- ing from BD, 79 from MDD and 79 HC underwent an MRI (3T) session. WM integrity was evaluated using TBSS with thresh- old free cluster enhancement (p<0.05) for diffusion tensor imaging (DTI) measures of fractional anisotropy (FA), axial (AD), radial (RD), and mean diffusivity (MD) [3]. We first performed an F-test to investigate differences between the three groups. Post-hoc T-test were then carried out. Age, gender, medication load and number of depressive episodes were entered as nuisance covariates. Results: Results pointed out bilateral widespread significant differences between the groups. Specifically, post-hoc T- test showed that compared to BD, MDD patients presented decreased FA and AD, and increased RD in several WM tracts. Patterns of increased MD were detected between BD and MDD in different WM tracts: specifically BD showed higher values of MD in posterior and right WM fibres, while MDD pre- sented increased MD in frontal fibre tracts. Both disorders compared to HC showed decreased FA and AD and increased RD in WM tracts previously associated to these disorders. Conclusions: This is one of the few studies directly show- ing differences in FA, AD, RD and MD between BD and MDD. Results provide strong evidence for the presence of WM al- terations in both MDD and BD, compared to HC, consistently with previous literature. Notably, BD and UD differ in in- creased MD pattern highlighting disruption in specific fibres. Indeed MD reflects the overall rate of water diffusion, al- lowing the investigation of brain structural and microstruc- tural integrity. Increases in MD are attributed to atrophy or changes in tissue density and could reflect different patho- physiological processes. This result may represent distinct neuropathological patterns and characteristics of the two disorders. Our hypothesis is to focus, not only on quantita- tive differences in DTI measures, but also on identifying spe- cific fibres involved in the distinctive neuropathological pro- cess underlying BD and MDD, and possible symptoms associ- ation. These results encourage the employment of DTI, also as a valuable modality in multimodal neuroimaging analy- ses, to enhance differential diagnosis and thus clinical prac- tice. References [1] Wittchen, H.U., 2012. The burden of mood disorders. Science 338 (6103), 15 5. [2] Wise, T., Radua, J., Nortje, G., Cleare, A.J., Young, A.H., Arnone, D., 2016. Voxel-based meta-analytical evidence of structural disconnectivity in major depression and bipolar dis- order. Biological psychiatry 79 (4), 293–302. [3] Smith, S.M., Jenkinson, M., Johansen-Berg, H., Rueckert, D., Nichols, T.E., Mackay, C.E., Behrens, T.E., 2006. Tract-based spatial statistics: voxelwise analysis of multi-subject diffusion data. Neuroimage 31 (4), 1487–1505. doi: 10.1016/j.euroneuro.2019.09.123 P.062 Interpersonal cognitive differentiation and in- terpersonal cognitive richness as mediators of self- reflectivity and neurocognition on negative symptoms in psychosis H. Garcia 1,∗ , A. Villaplana 2 , R. López-Carrilero 3 , E. Grasa 4 , A. Barajas 5 , E. Pousa 4 , G. Identity 6 , G. Feixas 7 , S. Ochoa 3 1 Sant Joan de Déu Research Institute, Parc Sanitari Sant Joan de Déu, Sant Boi de Llogrebat, Spain 2 Esplugues Mental Health Center, Parc Sanitari Sant Joan de Dèu, Sant Boi de Llobregat, Spain 3 Sant Joan de Déu Research Institute, Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain 4 Biomedical Research Institute Sant Pau IIB-SANT PAU, De- partment of Psychiatry, Barcelona, Spain 5 Centro de Higiene Mental Les Corts, Research Unit, Barcelona, Spain 6 Parc Sanitari Sant Joan de Déu, Sant Joan de Déu Research Institute, Sant Boi de Llobregat, Spain 7 University of Barcelona, Department of Clinical Psychol- ogy and Psychobiology, Barcelona, Spain Background: People with psychosis experience disruptions in personal identity that affect negative symptoms, but the complexity of this phenomenon should be addressed in an in-depth manner. Following the Personal Construct Theory, our aim was to examine the role of distinct dimensions of personal identity, as measured with the Repertory Grid Technique (RGT), within other well-known factors on psy- chological models of negative symptoms. Simple and dimin- ished narratives of self might result in poorer experiences of affect and volition, leading to negative symptoms [1]. Con- sidering that these narratives of self emerge from a cogni- tive structure, it is possible that this diminishment might be derived from a cognitive structure which is too simplistic and poorly elaborated. The richness of the cognitive struc- ture of personal identity, as measured with the RGT, is com-