Liste-39

MEDIAN EVOKED RESPONSES: STIMULATION MODALITIES FOR MIDLATENCY CORTICAL COMPONENTS

Rundshagen I, Schnabel K and Schulte am Esch J

Purpose: Evoked responses are used for examining the sensory system, but stimulation modalities are not standardised. This study evaluates midlatency components of median nerve evoked responses in relation to stimulation intensity in healthy females.

Methods: With IRB approval and informed consent 32 female patients (40±1Oy) were included in the study. SEP recordings at C4' (N20, P25, N35, P45, N50) vs. Fz followed electrical stimulation of the median nerve (3Hz, 200/average, bandpass 0.02-2kHz). The levels of stimulation intensity were: threefold sensory threshold (INT1), sensory and motor threshold (INT2), level of tolerance (INT3). Effects of stimulation intensity on latencies and peak-to-peak amplitudes were analysed by multivariate analysis of variance (Hotellings T-Square).

Results: Increasing stimulation intensity from INT1 to INT2 enhanced midlatency cortical amplitudes (except N35P45) significantly without changing latencies. Increasing stimulation at INT3 did not change the primary cortical complex, but components > 35 ms became identifiable in the whole sample except one subject. The intensity was comfortable for all subjects.

Conclusions: For monitoring midlatency components > 35 ms the authors suggest stimulation intensity close to individual tolerance level for optimal cortical responses. To increase knowledge about the sensory system further studies may electrophysiologically evaluate these components in combination with functional mapping techniques.