Pinna orientation determines the maximal directional sensitivity of bat auditory neurons.

The auditory response areas of 192 inferior collicular neurons (IC) of Eptesicus fuscus were studied under free field acoustic stimulation. The boundary of the auditory response area of a neuron expands with stimulus intensity (Fig. 1). However, there is a response center within each neuron's response area at which the neuron has the maximal sensitivity. All response centers of the 192 neurons are located within a limited space of the bat's contralateral auditory space. The position of the response center of a neuron changes with different pinna orientations (Figs. 2 and 3) providing a bat with versatility in maximizing the sensitivity of its echolocation system.