Basic NeuroscienceMultielectrode recordings from auditory neurons in the brain of a small grasshopper

- Small grasshopper auditory brain neurons were recorded with multielectrodes.
- Signal to noise ratio was higher with 12 μm tungsten compared to 15 μm copper wires.
- Stable recordings were achieved for 30 minutes and more.
- Spike sorting and collision analysis discriminated up to 5 units per recording.
- Unit identification by comparing extracellular to intracellular data is difficult.

BackgroundGrasshoppers have been used as a model system to study the neuronal basis of insect acoustic behavior. Auditory neurons have been described from intracellular recordings. The growing interest to study population activity of neurons has been satisfied so far with artificially combining data from different individuals.New methodWe for the first time used multielectrode recordings from a small grasshopper brain. We used three 12 μm tungsten wires (combined in a multielectrode) to record from local brain neurons and from a population of auditory neurons entering the brain from the thorax. Spikes of the recorded units were separated by sorting algorithms and spike collision analysis.ResultsThe tungsten wires enabled stable recordings with high signal to noise ratio. Due to the tight temporal coupling of auditory activity to the stimulus spike collisions were frequent and collision analysis retrieved 10-15% of additional spikes. Marking the electrode position was possible using a fluorescent dye or electrocoagulation with high current. Physiological identification of units described from intracellular recordings was hard to achieve.Comparison with existing methods12 μm tungsten wires gave a better signal to noise ratio than 15 μm copper wires previously used in recordings from bees' brains. Recording the population activity of auditory neurons in one individual prevents interindividual and trial-to-trial variability which otherwise reduce the validity of the analysis. Double intracellular recordings have quite low success rate and therefore are rarely achieved and their stability is much lower than that of multielectrode recordings which allows sampling of data for 30 min or more.