The conductivities of the extracellular space along the electrode tracks in the pedunculus and calyx and in part of the alpha-lobe of the mushroom bodies were found to be constant. In order to locate the synaptic areas generating these potentials, current source-densities (CSD) were calculated using the consecutively measured evoked potentials. These potentials were elicited by olfactory, mechanical and visual stimuli. Series of averaged evoked potentials (AEPs) were recorded along electrode tracks at consecutive depth intervals in different parts of the mushroom bodies of the bee. In order to analyse the functional properties of this neuropil field potentials were measured extracellularly. The intrinsic neurons (approximately 170,000/mushroom body) have very small axon diameters (0.1–1 μm) which makes it difficult to record their activity intracellularly. The mushroom bodies consist of layers of parallel intrinsic neurons which make synaptic contact with extrinsic input and output neurons.
Information processing in the mushroom bodies which are an important part of most invertebrate central nervous systems was analysed by extracellular electrophysiological techniques.
