The role of the FM component in shaping the number of impulses and response latency of inferior collicular neurons of Hipposideros armiger elicited by CF–FM sounds

•Stimulated with CF–FM sounds, the bat IC neurons discharge as SO or DO responders.•The FM component decreases the number of CF-elicited impulses of SO and DO neurons.•The FM component shortens the CF-elicited response latency of DO neurons.•Two possible mechanisms underlying the seemingly paradoxical results are proposed.•The biological relevance of these findings in relation to bats' hunting is discussed. Previous studies show that when stimulated with constant frequency–frequency modulated (CF–FM) sounds, the inferior collicular neurons of the leaf-nosed bat, Hipposideros armiger, either discharge impulses only to the CF component (single-on, SO neurons) or to both CF and FM components (double-on, DO neurons). In this study, we specifically determine the role of the FM component in shaping the number of impulses and response latency of these two types of neurons in response to CF–FM sounds. Adding the FM component to the CF sounds significantly decreases the number of impulses of both SO and DO neurons but shortens the response latency of DO neurons in response to the CF component of the CF–FM sounds. The possible neural mechanisms underlying these seemingly paradoxical observations are briefly discussed based on our preliminary intracellular recording studies. Biological relevance of these findings in relation to different phases of bats' hunting is also discussed.