Modeling the variability of the electromotor command system of pulse mormyrids

The electromotor neural system in weakly electric fish is a network responsible for active electroreception and electrolocation. This system controls the timing of pulse generation in the electrical signals used by these fish for extracting information from the environment and communicating with other specimens. Ethological studies related to fish mating, exploratory, submissive or aggressive behaviors have described distinct sequences of pulse intervals (SPIs). Accelerations, scallops, rasps, and cessations are four patterns of SPIs reported in pulse mormyrids, each showing characteristic temporal structures and large variability both in timing and duration. This paper presents a biologically plausible computational model of the electromotor command circuit that reproduces these four SPI patterns as a function of the input to the model while keeping the same internal parameter configuration. The topology of the model is based on a simplified representation of the network as described by morphological and electrophysiological studies. An initial ad hoc tuned configuration (S-T) was build to reproduce all four SPI patterns. Then, starting from S-T, a genetic algorithm (GA) was developed to automatically find the parameters of the model connectivity. Two different configurations obtained from the GA are presented here: one optimized to a set of synthetic examples of SPI patterns based on experimental observations in mormyrids (S-GA), and another configuration adjusted to patterns recorded from freely-behaving Gnathonemus Petersii specimens (R-GA). A robustness analysis to input variability of these model configurations was performed to discard overfitting and assess validity. Results showed that the four SPI patterns are consistently reproduced, both with synthetic (S-GA) data and with signals recorded from behaving animals (R-GA). This new model can be used as a tool to analyze the electromotor command chain during electrogeneration and assess the role of temporal structure in electroreception.Author summaryWeakly electric fish are a convenient system to study information processing in the nervous system. These fish have a remarkable sense of active electroreception, which allows them to generate and detect electrical fields for locating objects and communicating with other specimens in their surroundings. The electrical signal generated by these fish can be easily monitored noninvasively in freely-behaving animals. Activity patterns in this signal have been associated to different fish behaviors, like aggression or mating, for some species of the mormyridae family. In this work we use discharge patterns recorded from specimens of the Gnathonemus Petersii species along with synthetic data to develop a model of the electromotor command network. The model network is based on morphological and physiological studies in this type of weakly electric fish. The parameters of this model were tuned using a genetic algorithm to fit both synthetic and recorded activity patterns. This computational model allows to simulate the electromotor network behavior under controlled conditions and to test new hypotheses on the generation and function of temporal structure in the signals produced by weakly electric fish.

Electric sensing for underwater navigation

Underwater navigation in turbid water for exploration in catastrophic conditions or navigation in confined unstructured environments is still a challenge for robotics. In these conditions, neither vision nor sonar can be used. Pursuing a bio-inspired approach in robotics, one can seek solutions in nature to solve this difficult problem. Several hundred fish species in families Gymnotidae and Mormyridae have developed an original sense well adapted to this situation: the electric sense. Gnathonemus petersii first polarizes its body with respect to an electric organ discharge located at the base of its tail and generates a dipolar electric field in its near surroundings. Then, using many transcutaneous electro-receptors distributed along its body, the fish “measures” the distortion of the electric field and infers an image of its surroundings. Understanding and implementing this bio-inspired sense offers the opportunity to enhance the navigation abilities of our underwater robots in confined spaces bathed by turbid waters.