Adaptation of evoked auditory potentials: A midbrain through frontal lobe map in the unanesthetized cat

Abstract

Adaptation patterns of auditory potentials were investigated with stereotaxically oriented concentric bipolar electrodes at 4628 points in the brains of 18 unanesthetized but restrained cats. Binaural click stimuli were presented at rates of 1, 2, 5, and 10 and 20/sec through hollow ear bars. The results are presented as a map from P2-A21. Evoked auditory potentials were recorded in both lemniscal and extralemniscal structures. Adaptation, the decrement in amplitude of evoked potentials observed upon repetitive stimulation, was mot pronounced during the first few clicks. This rapidly occuring decrement was not considered most closely correlated with the learning process of habituation. Two major patterns of adaptation were observed: partial and complete. No potentials in the lemniscal structures adapted completely although some in the inferior colliculus and medial geniculate adapted partially. Many potentials recorded in extralemniscal structures adapted completely. Most extralemniscal structures exhibited non-adapting as well adapting potentials. However, certain ‘non-auditory’ cortical areas only produced potentials which adapted completely, and certain thalamic nuclei as well ad the subthalamus only produced potentials which adapted completely or partially. Contrary to earlier studies, potentials in lemniscal and extralemniscal structures adapted after a similar number of stimulus repetitions.