461. IMPAIRMENT OF THE ENHANCEMENT EFFECT OF PERCEIVED SPATIAL SEPARATION ON PREPULSE INHIBITION OF STARTLE IN FIRST-EPISODE SCHIZOPHRENIA AND CLINICAL HIGH RISK FOR PSYCHOSIS

Abstract Background Clinical high risk for psychosis (CHR) had significant PPI deficits similar to first-episode Schizophrenia (FES), in comparison with healthy control (HC). PPI deficiencies have been proven to represent both state and heritable features. PPI with poor attention modulation may be an endophenotype of schizophrenia and CHR. In the modified perceived spatial separation PPI paradigm (PSSPPI) can specifically enhance PPI; thereby PSSPPI is a more sensitive and robust index of PPI impairment, applying the effect of perceptual spatial separation, than perceived spatial co-location PPI (PSCPPI). And the enhancement effect of selective attention on PPI is significant in healthy subjects; however, this enhancement effect is impaired in patients with schizophrenia and CHR. Aims & Objectives We propose the separation effect value: (PSSPPI-PSCPPI) /(PSSPPI+PSCPPI), which can reflect the enhancement effect of selective attention on prepulse, and the higher of the value, the greater of the enhancement effect. We assume that the separation effect value maybe a promising objective index for preliminary identification of CHR. Method 53 FESs, 55 CHR individuals, and 53 demographics matched healthy controls (HCs) participated in this study. PSSPPI and PSCPPI were measured in the conditions with interstimulus interval of 120ms and 60ms. Results PSSPPI and PSCPPI were compared among the three groups separately, and the results showed that there was no difference between PSSPPI 120 and PSCPPI 120 in the FES group (p=0.932), as the same as PSSPPI 60 and PSCPPI 60 (p=0.3). However, there were significant differences in HC group, both interstimulus interval 60ms and 120ms (p<0.001). In the CHR group, there were difference between PSSPPI 120 and PSCPPI 120 (p=0.014), but there was no difference at interval 60ms (p=0.512). This result showed the enhancement effect of selective attention on PPI is impaired in patients with FES and CHR. But the enhancement effect in patients with CHR was retained at interval 60ms which maybe due to the impairment of function in CHR is not as severe as that in FES. One-way ANOVA showed that the separation effect value had significant difference in the 120ms paradigm (p=0.013) and 60ms paradigm (p=0.016) among three groups. Using the post hoc multiple comparisons, we found that the separation effect value was more lower in the CHR groups than HC groups，both inter-stimulus interval 60ms (p=0.02) and 120ms (p=0.01). However, other paired comparisons of the separation effect value among the FES, CHR and HC groups showed no statistical difference. Discussion & Conclusions This study, for the first time, proposes the separation effect value which can reflect the enhancement effect of selective attention on prepulse，and provides evidence showing that the separation effect value is lowest in the CHR group. Early identification and intervention in the CHR populations have provided huge advantage in improved symptom and functional outcomes. The separation effect value appears a promising objective indicator for preliminary identification of CHR population. In the future, more relevant studies are needed to explore the application of the separation effect value, such as the identification of CHR individuals and even the evaluation of treatment effects.