Background and Aims:
Reduced MMN amplitude is a robust finding in schizophrenia.
Most of the studies contributing to the research on MMN in schizophrenia has applied oddball paradigms with sinusoidal tones. 
The aim of this study was to investigate whether more complex stimulation can be more informative, than typical oddball paradigm, to study impairment in auditory processing in schizophrenia.

Methods:
35 patients with schizophrenia diagnosis (males=19; 29.5years; SD 8.4years) and 20 controls (males=11, 29.6years, SD 9.5 years) participated in the study. 24 patients received antipsychotic monotherapy, 12 polytherapy, 11 clozapine. 
The typical oddball (with pure-sinusoidal tones and single deviant to duration increment) and multi-feature (each stimuli consists of eight harmonics) with eight different deviants developed by Pakarinen et al.(2010)) paradigms were applied.

Results:
MMNs elicited with oddball and deviants from multi-feature paradigm: frequency, location, density and added noise were significantly reduced in schizophrenia group. Effects of clozapine, polytherapy and interaction between clozapine and polytherapy were observed for multi-feature paradigm deviants (duration: clozapine vs non-clozapine: F(1,31)=9.3; p=0.005; brightness: mono- vs polytherapy: F(1,31)=5.8, p=0.022; density: clozapine vs monotherapy group: F(1,31)=6.1; p=0.019). No difference between pharmacotherapy groups were found for oddball duration MMN.

Conclusions:
To sum up, only amplitude of MMN elicited by multi-feature but not oddball paradigm were able to differentiate between different pharmacotherapy subgroups. Reduced amplitudes of duration, density and brightness MMN elicited by multi-feature paradigm provides insight into interaction between impaired auditory processing and responsiveness to first and second line antipsychotic treatments.

15 - EFFECTS OF OPTIMIZING AUDITORY STIMULATION PARADIGM ON MMN AMPLITUDE IN SCHIZOPHRENIA PATIENTS