THE ROLE OF DENDRITES IN AUDITORY COINCIDENCE DETECTION

Coincidence-detector neurons in the auditory brainstem of mammals and birds use interaural time differences to localize sounds(1,2). Each ne uron receives many narrow-band inputs from both ears and compares the time of arrival of the inputs with an accuracy of 10-100 mu s (refs 3- 6). Neurons that receive low-frequency auditory inputs (up to about 2 kHz) have bipolar dendrites, and each dendrite receives inputs from on ly one ear(7,8). Using a simple model that mimics the essence of the k nown electrophysiology and geometry of these cells, we show here that dendrites improve the coincidence-detection properties of the cells. T he biophysical mechanism for this improvement is based on the nonlinea r summation of excitatory inputs in each of the dendrites and the use of each dendrite as a current sink for inputs to the other dendrite. T his is a rare casein which the contribution of dendrites to the known computation of a neuron may be understood. Our results show that, in t hese neurons, the cell morphology and the spatial distribution of the inputs enrich the computational power of these neurons beyond that exp ected from 'point neurons' (model neurons lacking dendrites).