Influence of temperature on tuning of primary-like units in the guinea pig cochlear nucleus.

The effect of temperature changes on the response area of primary-like single units recorded extracellularly in the anteroventral cochlear nucleus of the guinea pig was studied for cochlear temperatures in the range 27.4-40.3 degrees C, while maintaining a normal rectal temperature of 38.5 degrees C. A new approach to the cochlear nucleus was developed which involved opening of the temporal bone overlying the flocculus cavity and aspirating a small portion of the paraflocculus. Irrespective of characteristic frequency CF (0.8-16 kHz), hypothermia caused a reversible elevation of CF thresholds (1.6 dB/degrees C), a small loss of the sharpness of threshold tuning and reductions of the saturation and mean spontaneous rates. The CFs were unaffected, in contrast to single units in birds and cold-blooded animals. From a comparison of the effects of temperature on different species it is proposed that the processes that define CF and sharpness of tuning are different within a cochlea, and that these processes can be differentially influenced.