Inga Griskova-Bulanova1,2, Kastytis Dapšys1,2, Valentinas Mačiulis2,3, Sigita Melynyte1, Aleksandras Voicikas1
1Vilnius University, Life Sciences Center, Vilnius, Lithuania
2Republican Vilnius Psychiatric Hospital, Vilnius, Lithuania
3Vilnius University Medical Faculty Psychiatric Clinic, Vilnius, Lithuania
Auditory steady-state responses (ASSR) provide a non-invasive technique to assess neural synchrony at a particular frequency. Attenuated phase-locking (PLI) of ASSRs in gamma frequency range is observed in schizophrenia and in animal models for psychosis. The effect of clozapine, which is prescribed in cases of treatment-resistant schizophrenia, on ASSR in humans is not clear. The aim of this study was to evaluate the effect of clozapine use on phase-locking of 40Hz ASSR and state-sensitivity in schizophrenia patients. 48 male patients with schizophrenia (according to ICD-10 criteria) were recruited from the in-patients of Republican Vilnius Psychiatric Hospital. Patients were divided into two groups: (1) resistant to standard antipsychotic medication and treated with clozapine (Cloz, n=23); and (2) responsive to standard antipsychotic treatment (NCloz, n=25). ASSRs to click stimuli at 40Hz were recorded using 9 channels in eyes open and eyes closed conditions, with 60 stimuli presented binaurally per condition. After conventional cleaning procedures, epochs of 700 ms were created starting at 100 ms prior to the stimulus onset and lasting for 600 ms post-stimulus. ASSRs were analyzed from Cz location, showing maximal activity. Mean phase-locking index (PLI) within 38-42Hz window was calculated for 100 ms bins and subjected to RM-ANOVA with time bin and task as within-subjects factors and group as a between-subjects factor. Significant interaction of condition (eyes open vs eyes closed) and group (Cloz vs NCloz) factors (p=0.038) was observed, suggesting that in Cloz group subjects tended to have lower PLIs in open eyes (p=0.08), which increased with eyes closure (p<0.001). In NCloz group, PLIs did not change with eyes closure (p>0.05). Our data propose that state-sensitivity of 40 Hz ASSRs vary depending on the treatment in patients with schizophrenia and subject receiving clozapine showing response increase with eyes closure in contrast to those on standard antipsychotic treatment.