METHOD FOR DETERMINING INDIVIDUAL NEURON SIZE IN SIMULTANEOUS SINGLE-UNIT RECORDINGS

A technique for estimating the size of neurons is based on extracellul ar recordings with paired-electrode sets. Simultaneous single-unit rec ordings are obtained from the dragonfly mesothoracic ganglion. It is a ssumed that the ganglion is a passive electrical environment, where sp ike amplitudes decrease with the inverse of distance squared, and spik e angles (widths) increase linearly with distance from the cellular so urce to the recording electrodes. Starting with the recorded spike amp litudes and angles for each cell, a numerical algorithm is iterated to estimate the true value of the amplitude and angle minus these passiv e electrical distance effects. The resolved amplitude is a direct, con sistent estimate of the size of each recorded neuron. The results indi cate that a dichotomy of small and large cells is recorded in roughly a 2:1 ratio. The dichotomy of cell sizes is consistent with the availa ble histological data, although a larger ratio of small to large cells (similar to 10:1) would be expected. Thus, a sampling bias for large cells is apparent, which may be reflective of the larger soma/proximal geometries of such cells. As the technique determines the size of eac h individual neuron, such biases: are eliminated from population studi es of the neural tissue. Furthermore, knowledge about the size of each individual neuron permits more detailed analyses of the interactions and contributions of single cells within a network of cells based upon size.