, 2002 and Lichtenstein et al., 1990). However, in the auditory system, the eighth nerve fibers conveying auditory information from the cochlea to the cochlear nucleus show symmetrical discharge patterns in response to ascending and descending portions of a frequency-modulated

signal, which suggests their lack of selectivity to the direction of FM sweeps (Britt and Starr, 1976 and Sinex and Geisler, 1981). http://www.selleck.co.jp/products/Paclitaxel(Taxol).html This implies that DS neurons have to be constructed by neural circuitry mechanisms in the central pathway. The core central auditory pathway includes the cochlear nuclei, the central nucleus of the IC, the ventral portion of the medial geniculate body, and the primary auditory cortex (Winer and Schreiner, 2005).

It is generally believed that DS is constructed in the subcortical nuclei of auditory processing (Britt and Starr, 1976, Casseday et al., 1997, Clopton and Winfield, 1974, Fuzessery and Hall, 1996 and Poon et al., 1992). However, the exact location in which DS is constructed is somewhat controversial: Selleck Lenvatinib neurons with asymmetrical discharge patterns to ascending and descending portions of FM signals were found as early as in the cochlear nuclei in cats (Britt and Starr, 1976 and Erulkar et al., 1968), whereas they are not prominent in the cochlear nuclei of bats or rats (Moller, 1969, Moller, 1974, Suga, 1964 and Suga, 1965). To avoid such complications caused by species’ differences, we performed systematic studies at different stages of central auditory processing in rats. Our recordings in the cochlear nuclei of the rat only demonstrate a negligible DS compared to that of IC neurons: compared to 0.75 of IC neurons, the maximal absolute DSI of CN neurons is 0.21, which is less than 0.33, the criteria for strong

direction selectivity. The percentage of DS neurons in the rat’s IC has been addressed by several studies that used different FM stimuli and yielded different results, ranging from 10% to 80% (Felsheim and Ostwald, 1996, Poon et al., 1991, Poon et al., 1992 and Vartanian, 1974). Our Rutecarpine results show 39.3% of sampling sites from multiunit recordings, and 51.6% of the recorded neurons from cell-attached recordings demonstrated strong DS, with their DSIs greater than 0.33. The topography of DS neurons inferred from our data demonstrates an increased correlation of DSI and CF along the ascending auditory pathway (correlation coefficients: −0.12 in CN, −0.73 in CNIC, and −0.81 in MGBv), compared with −0.87 in A1 (Zhang et al., 2003). The ratio of upward direction-selective neurons to downward direction-selective neurons also differs among different species, as well as their correlation with CFs.