[Origin of the auditory middle latency response Pa in guinea pig]

The cortex of guinea pig was divided into five regions and respective ablation of the different regions combined with local infiltration of kainic acid on the cortex was made to investigate the relationship between the different part of the cortex and MLR. The results of ablation showed that the main component of the MLR, wave Pa, still appeared unless the primary auditory cortex contralateral to the stimulated ear was removed. With local application of kainic acid it was further suggested that the Pa mainly originates from the neurons in the primary auditory cortex and that subcortical auditory structures and their projected fibers do not contribute to the Pa.