An estimator for the electrotonic size of neurons independent of charge equalization time constants

Electrotonic properties are important aspects of neuronal function but have been difficult to estimate without accurate morphological reconstruction. The complexity of the branching dendritic cables often gives charging curves composed of a very large number of exponential functions, making it difficult to distinguish the time constants that are needed for electrotonic estimates. We describe an estimator P for the electrotonic size of neurons based on simple measures from voltage and current clamp recordings that does not rely on the higher rank exponential components of the response. Our estimator gives a bounded scale for the electrotonic size of the cell and can be used for categorization and comparison when morphology is not available.