HOW TO EXTRACT THE SPATIAL CORRELATION OF AUDITORY CORTICAL EVOKED POTENTIALS ON MULTIPLE SCALP ELECTRODES IN TINNITUS PATIENTS

Abstract

Tinnitus affects 10–15% of the population and tends to increase in frequency among older ages. The published reports have converged on that tinnitus is the sustained neuroplastic changes with aberrant activity residing in the auditory and nonauditory nervous systems that cause the sensation and problem of tinnitus. Clinically tinnitus remains as a subjective symptom and cannot be evaluated objectively. Our previous study has demonstrated the significantly different intensity dependence of auditory cortical evoked potential (ACEP) amplitudes to pure-tone stimuli recorded at some midline scalp electrodes between normal controls and tinnitus patients. Although ACEP test has been well known for its excellent temporal resolution of milliseconds and the latency and amplitude of ACEPs give ample information about the auditory processing of tinnitus, these measurements at each electrode deliver insufficient information about the spatial correlation among different cortical locations. According to the neurophysiological model of tinnitus, temporal and spatial information are both necessary and complementary to study the underlying mechanisms of problem tinnitus. Thus the purpose of this study was to demonstrate the spatial presentations of ACEP N1–P2 of normal controls and tinnitus patients. In this work, a program has been developed to translate the ACEPs recorded at 30 scalp electrodes to a two-dimensional presentation of isoelectric topography and current source density. The differences of intensity dependence about N1–P2 noted with previous study are reviewed on the two spatial presentations and compared between control subjects and tinnitus patients, while the patterns of correlation are demonstrated and compared with those recorded by functional brain imaging techniques like PET and fMRI.