Association Between The Loudness Dependence of The Auditory Evoked Potential and Age in Patients With Schizophrenia and Depression

Abstract Background The loudness dependence of the auditory evoked potential (LDAEP) reflects serotonin neurotransmission. Abnormality in serotonergic activity is dominant in patients with schizophrenia (SCZ) and major depressive disorder (MDD). Patients with SCZ show weak LDAEPs, reflecting high serotonergic activity. Some patients with MDD show high serotonergic activity. Although the changes in serotonin neurotransmission in the aging brain of SCZ and MDD have been observed, the relationship between central serotonergic activity and age remains unclear. The present study compared LDAEP between patients with SCZ and MDD, and healthy controls (HCs). We further examined whether age correlated with LDAEP and clinical symptoms, controlling usage of serotonin-related drugs. Methods A total of 105 patients with SCZ and MDD were enrolled (54 patients with SCZ and 51 patients with MDD). Thirty-five HCs were recruited. LDAEP was measured on midline channels (Fz, FCz, Cz, Pz, and Oz) among 62 electroencephalography channels. Positive and negative symptoms were assessed in patients with SCZ while depression and/or anxiety symptoms were evaluated in patients with MDD and HC. Results Patients with SCZ and MDD showed smaller mean LDAEP than that of HC group (p < 0.001). Age was positively correlated with LDAEPs in patients with SCZ and MDD. Conclusion Decreased serotonergic activity with aged brain could be indicated by LDAEP in patients with SCZ and MDD. Changes in LDAEP according to age would be a compensatory mechanism across progression of disease in SCZ and MDD.