Effect of Different Sites of Recording Electrodes on Auditory Evoked Potentials in Healthy Adults

OBJECTIVE: This study was designed to investigate the effect of different sites of recording electrodes on auditory evoked potentials (AEPs) in healthy adults and to analyse these potentials properly. METHOD: Eleven healthy adults, 7 males and 4 females, without any history of disease or conditions causing hearing difficulties were selected. AEPs were performed on these subjects with 4 different methods, i.e. different recording sites, Cz-Ai, Cz-Fpz, Ai-Ac, and Ai-Cs7. Auditory stimulation was given by rarefaction clicks of 75dB intensity and 11.1 Hz frequency, and responses were recorded with surface electrodes. RESULTS: The amplitudes of peak I and V were larger with vertical recordings, that is the vertex-auricle (Cz-Ai) or vertex-7th cervical spine (Cz-Cs7) recordings, compared to horizontal recordings of both auricle (Ai-Ac) or extracephalic electrodes. The largest amplitude ratio of peak V/I was with vertex-7th cervical spine (Cz-Cs7) recording. CONCLUSION: Changes in AEPs with respect to the sites of recording and reference electrodes are thought to be due to the vector of brain stem auditory nuclei and pathways. It might be helpful to consider these changes in the evaluation of brain stem lesions.

Vestibulocollic Reflex Evoked by Abrupt Free Fall of the Head

Vestibulocollic reflex(VCR) which stabilizes head position in space is essential for an adequate motor performance, and maintenance of balance and posture. The purpose of this study was to measure the VCR in brain stem lesion patients and to evaluate the usefulness of the VCR study in the evaluation of brain stem lesions. The VCR evoked by free fall of the head was measured by the electromyographic signal of the sternocleidomastoid muscles. Twenty normal and ten brain stem lesion subjects were studied by lying supine with the head cradled in a sling, and the VCR was evoked by an abrupt head drop while the sling was released. The electromyographic signal was recorded with surface electrodes from the sternocleidomastoid muscles. In normal subjects, the initial small burst with an onset latency at 20.61+/-3.25 msec was obtained followed by the later larger burst of sternoceidomastoid electromyographic response. But in the subjects with a brain stem lesion, the initial latency was delayed to 46.10+/-10.65 msec and the waveform was smaller and dispersed than that of the normal subjects. The VCR evoked by free fall of the head showed delayed latency and dispersed waveform in patients with a brain stem lesion. This method could be used for the evaluation of brain stem lesions.