Intracellular in vivo recording of inferior colliculus auditory neurons from awake guinea-pigs.

Intracellular recordings of identified inferior colliculus (ICc) auditory neurons, were analyzed in in vivo awake, chronically implanted guinea-pigs. The passive membrane characteristics as well as the spontaneous and click evoked synaptic potentials and spike activity, were studied. The injection of current pulses revealed little, if any, adaptation and membrane voltage shifts that outlasted the electrical stimuli. The spontaneous action potentials, observed in all the units studied, were of the short-duration type. During wakefulness, spontaneous synaptic potentials of higher amplitude were observed in comparison to the anesthetized preparation as well as an enhanced firing rate. The click evoked synaptic potentials far outlasted the sound (click, 0.1 ms) duration. The binaural, contralateral and ipsilateral sound stimulation evoked different sequences of synaptic potentials and firing. This was mostly in agreement with studies of extracellular recordings from the ICc, in anesthetized and behaving animals.