Integration in the crayfish antennal neuropile: topographic representation and multiple-channel coding of mechanoreceptive submodalities.

(1) Response patterns of interneuron populations in the antennal neuropile of the crayfish have been investigated by extracellular recordings made with a single electrode. Mechanical stimuli of the antennae are divided into submodalities and topographically represented. The submodalities include large movements of the entire antenna, directional aspects of movements and vibrations, and vibratory stimulation up to click repetition rates of 100. (2) Interneuron output is always patterned, ranging from simple bimodal types to complex multimodal patterns that extend over 40 msec. The interneuron output is "noisy" due to short- and long-term fluctuations in sensitivity producing temporal fluctuations in both output probability and output patterns. The response latencies both within and between populations cluster around several fixed latencies. (3) The axons of a group of neurons, sensitive to the same submodality, are located together and consequently can be recorded with a single electrode. Responses from the interneurons composing a population are similar in response to nonoptimal stimulation, but are synchronized and of high probability to optimal stimulation.