Negative temporal summation of the responses to pairs of tone bursts in albino mice inferior colliculus

Abstract

The extracellular activities of single units in an inferior colliculus of narcotized albino mice have been studied. As a stimuli pairs of best frequency (BF) tone bursts with different duration have been used and forward masking has been studied. The test tone usually has a 40 ms duration at intensity 5 dB above threshold. The intensity and duration of the masker could be changed. It was shown that the forward masking essentially depends upon the duration of the first burst. In many cases, the negative temporal summation can be seen. The increase in the duration of first burst (or masker) leads to the decrease in the whole response. Moreover, the BF tone burst which did not evoke any spike response could inhibit the response to the second (test) tone in some cases. Therefore in many units the inhibitory threshold was lower than the excitatory threshold even at the best frequency. The local application of bicuculline through a multibarrel-electrode increased the pulse activity considerably. However, the effect of forward masking usually left even after an inhibitory antagonist (bicuculline) application. [Work supported by grants 39970251 from NSFC, T010360056 from the Foreign Expert Bureau of the State Council of China, and 02-04-3900 from RFBR-NSFC.]