Basic determinants for FM responses in the inferior colliculus of rats

Abstract

The response of 835 click-sensitive neurons in the inferior colliculus (IC) to ramp frequency modulated (FM) tones was studied in the anaesthetized rat. More than 70% of the cells were sensitive to the FM sound, and over 25% were "FM specialized". Systematic variations of the stimulus parameters showed that sweep velocity, sweep range, and intensity of the FM signal were the 3 basic determinants for the unit response. For an "FM specialized" cell, the response pattern to each of the parameters was either monotonic or bell-shaped. The population statistics of response patterns to the FM parameters, including the tuning factors, were generated. A stimulus domain was proposed to represent the "receptive space" of the FM cells.

Spectrotemporal Receptive Fields in the Inferior Colliculus Revealing Selectivity for Spectral Motion in Conspecific Vocalizations

“…Neurons in the IC of the bat are tuned for conspecific natural sounds Directional selectivity for FM sweeps has been a recurrent theme in studies of the auditory system in a variety of mammals for more than 30 years (Grinnell and McCue, 1963;Suga, 1964Suga, , 1968Clopton and Winfield, 1974;Mendelson and Cynader, 1985;Phillips et al, 1985;Poon et al, 1991;Fuzessery, 1994;Gordon and O'Neill, 1998;Poon and Yu, 2000). FM directional selectivity has been of particular interest in studies of bats attributable to the universal presence of brief downward-sweeping FM components in their echolocation calls (Pollak and Casseday, 1986;Neuweiler and Schmidt, 1993).…”

DSCF Neurons Within the Primary Auditory Cortex of the Mustached Bat Process Frequency Modulations Present Within Social Calls

“…Bell-shaped response distributions that are elicited by changes along multiple FM parameters have proven elusive in several animal models and at different levels of the auditory system O'Neill 1998, 2000;Heil et al 1992a;Mendelson et al 1993;Nelken and Versnel 2000;Poon et al 1991;Shamma et al 1993). Likewise, variations in two of our parameters (slope and bandwidth) did not yield bell-shaped response curves from DSCF neurons.…”

“…Likewise, variations in two of our parameters (slope and bandwidth) did not yield bell-shaped response curves from DSCF neurons. Most notably, one study of linear FM response characteristics in the rat IC used a procedure very similar to that in this study to independently examine IC neuron responses to shifts in FM slope, bandwidth, and amplitude parameters (Poon et al 1991). Bell-shaped distributions along all three parameters were obtained for only 11% of neurons in the rat IC.…”

“…Neurophysiological studies of the CN of cats, however, have demonstrated that 72% of neurons in this region have a DFM preference that is dependent on FM slopes (Britt and Starr 1976). Sixty-one percent of rat IC neurons are selective for direction, slope, and bandwidth (Poon et al 1991). Neurons in the MGB of the cat also display a directional preference for DFMs that is slope dependent (Purser and Whitfield 1972).…”

“…Thus inhibition shapes both frequency tuning and slope selectivity in the IC, much as it does in the AI of the pallid bat (Razak and Fuzessery 2006) and, presumably, the mustached bat. IC (or avian auditory midbrain) neuron responses to calls and FMs in other species such as cats (McAnally and Calford 1989), rats (Lee et al 2002;Poon et al 1991), and songbirds (Woolley and Casseday 2005) similarly reflect cortical (or avian auditory forebrain) responses to calls and FMs.…”