Decision letter: Peripheral sensory coding through oscillatory synchrony in weakly electric fish

Abstract

The mormyrids are a family of fish that can generate and detect weak electric fields that they use to navigate and communicate. Each species in this family produces its own distinct shape of electrical signals. Other fish detect these signals using structures called receptors, which then send information to the brain in the form of an electrical nerve impulse. Previous research showed that different species of fish respond to different aspects of the electric fields they detect, depending on the receptor types that they have evolved. For example, some species have ‘spiking receptors’ that send a spike of activity to the brain at the start or end of a detected electrical pulse. This allows the fish to detect subtle changes to the shape of the detected electric field. Other species have sensors known as oscillatory receptors; these send a continuous wave of nerve activity to the brain even when no electric field is detected. It is not clear exactly how oscillatory receptors work or what the roles of these different receptor types are. Baker et al. have now recorded the activity of the receptors of mormyrid fish as they were exposed to electrical fields that mimic the signals they are normally exposed to in their daily environment. The recordings confirmed previous results that suggest that species with spiking receptors are able to detect variations in the shapes of electrical signals produced by other fish because the receptors produce spikes of activity at the start or end of a detected signal. This response pattern allows their brains to analyze the signal shape. In contrast, Baker et al. found that when oscillatory receptors detect a new electric field, they reset their pattern of nerve activity, causing multiple receptors to briefly synchronize their activity. This enables the fish to detect where a signal has been sent from. However, the oscillatory receptors are unable to detect any variations in the shape of the detected electric signal. The oscillatory receptors are most sensitive to certain electric field patterns that are produced by large groups of a single species of fish. Further experiments showed that the fish also change their behavior when these particular electric field patterns are detected. Why some species of mormyrids have spiking receptors while others have oscillatory receptors is unknown. It is also unknown how the brain processes oscillatory receptor activity. Future studies will investigate whether these two receptor types may be linked to differences in fish's social behavior, and how the neural networks for processing sensory information differ between the two types of fishes.