Effects of antidepressive therapy on auditory processing in severely depressed patients: a combined MRS and MEG study

Alterations in brain metabolism as well as in brain function in different brain areas can be observed in severely depressed patients.

The present study combined proton magnetic resonance spectroscopy (1H MRS, n=16; healthy controls n=27) and magnetoencephalography (MEG, n=17, controls n=18) of the left auditory cortex in severely depressed inpatients pre- and post successful antidepressive therapy. For MEG recordings, patients were stimulated with trains of 4 successive vowels or 4 sine tones, respectively. For each of the 4 stimuli, the amplitude and latency of the N1m was calculated. As a measure of habituation the decrease of the individual amplitudes of the second, third and fourth N1m compared to the first N1m was calculated.

Prior to therapy, a subset of patients presented clearly disturbed auditory processing to stimuli (missing of distinct N1m1 and subsequent habituation; 5 of 17 patients (vowels) and 9/17 (tones, respectively)). After treatment, compared to controls, a normalized habituation pattern was observed in all patients for vowels, but not for tones. In contrast, MRS revealed no significant differences between the metabolite concentrations of patients and healthy controls in both measurements.

Depression may be accompanied by impaired auditory processing, which seems to improve with reduction in depressive symptoms. Auditory cortical dysfunction probably reflects only a part from more widespread aberrations of brain function occurring with severe mood disorder.