Disturbances of the Process of Synaptic Elimination and Its Reflection in the Wave N170 of Auditory Evoked Potential (AEP) in First Psychotic Episode of Paranoid Schizophrenia

In this work the response of cortical structures to auditorystimuli of different emotional significance (verbal stimuli associatedwith delusions and hallucinations and neutral ones) was investigatedin healthy controls (n = 15;7 males, 8 females) and in patients with paranoid schizophrenia(n = 24; 11 males, 13 females)in N170 component of the auditory evoked potential (AEP), participantsof both groups had higher or specialized secondary education andnearly equal level of social well-being. In norm, an amplitude increaseand latency shortening of N170 wave in the right central-parietalregion for emotionally significant stimuli was found, which meansthe greater level of cortical activation for this type of stimuli.Along with the general decrease in cortical activation peculiarto paranoid schizophrenia patients, which is well known in scientificliterature in this ERP component, our study revealed a simultaneousincrease in both ERP parameters- amplitude and latency in frontalareas and their decrease in central and temporal areas- a phenomenonthat we called the paradox effect (PE). PE in patients developsin response to emotionally significant verbal stimuli, which innorm cause increased activation. Thus, the study confirms our hypothesisthat PEs are found on auditory ERPs as well as on visual ERPs, whichwe found earlier in previous studies. The fact that PE is observedat the N170 wave of the auditory evoked potential (AEP), i.e., atthe same second perceptual stage as in the visual (VEP), may indicate thatthis response appears to be general principle for all modalities.However, because the auditory stimulus is shorter and more compactthan the image, the response is earlier. In this regard, the PEto the auditory stimulus develops on N170 wave, whereas in visualmodality it develops on later P200 component. Thus, in schizophrenia,a “conflict” between excitation and inhibition is detected alreadyby 170 ms after stimulus presentation in response to significantstimuli, resulting in the PEs development. The identity of PEs detectedin schizophrenia on VEP and AEP is also evidenced by the data onthe similar character of cortical excitation with simultaneous increaseor decrease of both N170 parameters. It is supposed that the revealedviolation reflects the pathological process of synapse eliminationpeculiar to schizophrenia, which results in an excess of synapsesin frontal areas combined with their deficit in central corticalareas.