Neurophysiological evidence of movement of chronically-implanted fine wire electrodes in recordings of field potentials in hippocampus

Abstract

Fine-wire electrodes, typically used to record single unit activity in freely-moving animals, were implanted chronically under electrophysiological guidance in the CA1 and dentate areas of the rat hippocampus. Monitoring of the CA1 and dentate field potentials from these electrodes in response to radiatum and perforant path stimulation respectively over days showed that the evoked response in CA1 frequently underwent a transition to a response typical of more ventral (densritic versus somatic) recording, while the response in dentate remained unchanged. Although, on the basis of histology, recording electrodes in both hippocampal regions appeared equally likely to have moved small distances relative to the brain, the effect of the movement in CA1 was more critical due to the fact that its depth profile is more sensitivie to small vertical displacements than is the corresponding dentate profile.