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Auditory steady-state responses (ASSRs) are widely applied to test brain's ability to follow external stimulation in neuropsychiatric disorders. It is known that ASSRs are related to GABAergic transmission. Female sex steroid homones - both estrogens and progesterone - affect functioning of GABAergic system. However, it is not known how these hormones affect brain's ability to entrain. This study was designed to test the ability to synchronize to 40 Hz stimulation during different phases of the menstrual cycle. Twenty-eight healthy females participated in the research during one of the menstrual cycle phases: (1) early follicular; (2) late follicular; (3) and mid-luteal. Auditory 40 Hz trains of 500 ms were delivered binaurally and EEG was recorded. Time-frequency analysis of the data was performed and phase-locking index, evoked amplitude and total intensity measures were extracted and decomposed by non-negative multi-way factorization. Additionally, alpha power of the baseline period was calculated. Parameters of ASSR were increasing in a linear manner with increasing levels of 17β-estradiol and largest estimates of ASSR parameters were obtained in the late follicular phase, smallest - in the mid-luteal phase. Alpha power values were highest in the late follicular phase and lowest in the mid-luteal phase, pointing to lower arousal level in the late follicular phase. We speculate that increased 40 Hz ASSRs during mid-cycle might be related to the level of general arousal and specific GABA-mediated changes during the menstrual cycle. The results suggest that the ability to entrain to 40 Hz stimulation depends on the phase of menstrual cycle. This should be taken into account, particularly when ASSRs are used in clinical practice, comparing patients and healthy subjects.

Early effects of risperidone (2.5 +/- 1 mg/day) on auditory information processing were investigated in 9 neuroleptic naive patients with schizophrenia spectrum disorders and 9 healthy controls by using event-related potentials (ERPs). ERPs were elicited during active auditory "oddball" paradigm and were recorded before and after two weeks of treatment. Baseline P3 latencies were significantly delayed in patient group. Risperidone treatment did not change P3 amplitudes and latencies. However, P2 amplitudes were reduced in parallel with the clinical improvement measured by Positive and Negative Syndrome Scale (PANSS). Although risperidone did not change neural bases of active attention after two weeks of treatment, the reduction of P2 amplitude suggests that risperidone may affect auditory information processing in patients with schizophrenia spectrum disorders who never have been exposed to antipsychotic treatment.

ERPs could be helpful in the objectification of many psychological measures. In the last few decades one of the most commonly used ERPs has been the mismatch negativity (MMN) potential. It may be used to detect cognitive dysfunction in patients suffering from schizophrenia, dementia, depression, and can also be successfully applied in treatment monitoring. Nevertheless, changes of MMN parameters (prolongation of latency or reduction of amplitude) are not sufficiently specific to help to diagnose particular diseases. In this study we looked for more strict and specific MMN characteristics selective for schizophrenia. Fifteen healthy human subjects and twelve suffering from schizophrenia spectrum disorders were studied. Two new parameters were considered: the speed of ascending part of MMN slope (SAS) and the half area of the MMN wave. These two measures could differentiate the early stages of cognitive processing disturbances in schizophrenia spectrum disorders.