[Study of topographic mapping of the auditory middle latency response in the guinea pigs]

Topographic mapping techniques were applied to study the auditory middle latency response (MLR) in 10 awake guinea pigs. Fourteen holes (1mm in diameter) were drilled through the skull regions and epidural electrodes were fixed on the skull with the dental cement, then auditory MLR were recorded with 13 electrodes, and MLR brain maps were obtained with a concerto system. Our result supports the hypothesis of multiple MLR generators. The main components are wave A, wave B and wave C. The foci localise the temporal lobe contralateral to the stimulated ear. The other components are wave M- and wave M+. The foci localise parietal and occipital lobes. Each wave responds differently to procaine. The result suggests that wave A, wave M- and wave M+ are generated from the subcortex, while wave B, wave C generated from the cortex.