抄録
Animals utilize a difference in sound arrival time between two ears (interaural time difference: ITD) for the sound source localization along the horizontal axis. In birds, ITDs are first calculated in neurons of nucleus laminaris (NL) by detecting the coincidence (CD) of binaural synaptic inputs. Previously, we showed in the brain slice preparation of the chicken that CD is improved by the EPSP acceleration due to the activation of low-threshold K+ currents and hyperpolarization-activated cation currents; being acute enough to encode physiologically relevant ITD of the chicken (<0.2ms). Because ITD sensitivity of behaving chicken is not yet reported, we examined the characteristic frequency and ITD sensitivity of NL neurons in anesthetized chicken (posthatch 1-6 days). We made extracellular recordings by utilizing a tungsten electrode inserted into a glass pipette, and the recording site was marked by a fluorescent dye (DiI) filled in the pipette. Pure-tone or white-noise stimuli of 70ms duration were presented with earphones, and their ITDs were changed systematically. We found that the response of NL neurons varied periodically with ITDs, and the cycle matched that of the stimulus tone. The acuity of ITD detection, evaluated with the maximum slope of ITD function, was almost equivalent to the acuity of CD observed in the in-vitro study. We will further examine the relationship between the ITD sensitivity and the characteristic frequency of NL neurons. [Jpn J Physiol 54 Suppl:S166 (2004)]
