Changed Acoustic Evoked Neuromagnetic Responses can be Recorded in Schizophrenic Patients with Auditory Hallucinations

There is an indication that central processing in the auditory system is changed in schizophrenics with auditory hallucinations. Otoacoustic emissions generated from cochlear hair cells are a valuable indicator for the functioning of efferent and afferent pathways in the auditory system. They can be recorded easily without strain for the test persons or patients. To test whether auditory information processing is delayed or otherwise changed in schizophrenia, auditory evoked magnetic fields (AEF) were evoked with tone bursts (1 kHz, duration 50 ms, rise time 5 ms, intensity 70 dB SPL; series per 200 single bursts with random interstimulus intervals) in schizophrenic patients with auditory hallucinations (n=32) and in healthy controls (n=40). Two recording sessions were performed for each person. Tone bursts were applied via an acoustically tested tube and funnel system to the contralateral ear of the test person. AEF were recorded with the Philips 2×31 channel double Dewar device (spherical sensor plate with a diameter of 140mm). The cryostat was placed over the temporal cortex contralaterally to the stimulated ear. AEF were evaluated with the CURRY program. For better recognition of the relevant signals, raw data were filtered digitally with a Fourier filter. The patients had suffered for more than 2 years from schizophrenia and were receiving neuroleptic treatment. Most of the patients had no hallucinations during the measurements, only a subgroup of 6 reported on hallucinations during the test. In healthy controls, AEF typically consisted of 4 prominent components, P50m, N100m, P160m, and P200m with latencies resembling the numbering of the components. Significant changes of the AEF, however, were found in schizophrenics: the latency of the AEF component N100m was prolonged and typical components (especially the P160m and P200m) were often missing, although there were no hallucinations during the trials. The data imply that auditory information processing is influenced during auditory hallucinations in schizophrenics. Tests will be repeated in each patient in a hallucination-free period to prove if the changes in AEF persist after ending neuroleptic treatment.