AN INVIVO TECHNIQUE FOR 3-DIMENSIONAL FIELD-MAPPING IN THE RODENT SPINAL-CORD

The purpose of this investigation was to develop a reliable method for in vivo mapping of small exogenously applied electrical fields in the mammalian spinal cord. Experiments were performed in vitro to validat e the technique in addition to recordings made in vivo on normal and s pinal cord injured rats. Sine waves of 1.5-50 muA and 0.5-50 Hz were u sed for stimulation. Field gradients were measured with a lock-in diff erential amplifier. Glass recording micro-electrodes were used for in vivo experiments. The accuracy of the technique was found to be highly dependent on the waveform of the current and impedance matching betwe en the recording electrodes. Recordings made in vivo demonstrated that measured fields were linearly related to the intensity of stimulation . Field gradients were not influenced by stimulation frequencies of 5- 50 Hz. Estimates were made of the influence of the surgical exposure o n the measured gradients. Our results demonstrate that small electrica l fields can be accurately mapped in vivo and interpolated throughout a broad range of intensities and frequencies.