Method for determining individual neuron size in simultaneous single-unit recordings

A technique for estimating the size of neurons is based on extracellular recordings with paired-electrode sets. Simultaneous single-unit recordings are obtained from the dragonfly mesothoracic ganglion. It is assumed that the ganglion is a passive electrical environment, where spike amplitudes decrease with the inverse of distance squared, and spike angles (widths) increase linearly with distance from the cellular source to the recording electrodes. Starting with the recorded spike amplitudes and angles for each cell, a numerical algorithm is iterated to estimate the true value of the amplitude and angle minus these passive electrical distance effects. The resolved amplitude is a direct, consistent estimate of the size of each recorded neuron. The results indicate 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 available histological data, although a larger ratio of small to large cells (approximately 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 each individual neuron, such biases are eliminated from population studies 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.