Sensory flow in active electrolocation

Research Areas: 

African mormyrid fish (Gnathonemus petersii in Fig 1A) are endowed with an electric sense which is used for navigation, prey detection and communication. Pulsed discharges of their electric organ (EOD) build up an electric field in the vicinity of the fish (Fig 1B). Objects within this field modulate the current distribution across the body surface, the so called electric image. This 2 dimensional, conductivity-dependent modulation is sensed with a distributed array of electroreceptors embedded in the skin of the animal.

In this project we intend to describe and analyse the influence and contribution of sensory flow to this sensory system. Moreover we are interestred how electric images and the related sensory flow are coded in the central nervous system of Gnathonemus petersii.


Methods and Research Questions: 

I. Analysing sensory related behavior in active electrolocation: Linking motor patterns to electric flow information

Previous research on electric images was limited to immobilized fish and thus did not describe the influence of spatio-temporal information potentially available to the animals. Here we advance to more naturalistic conditions by filming unrestrained Gnathonemus petersii (N=6) during object exploration (metal cubes of 1, 8 and 27 cm3) at IR-illumination. The high-speed video acquisition was triggered by the animals own EOD. Thereby we gather detailed spatial and temporal information linked to the pace of the animals sensing interval.

Body kinematics and the geometric relationship between the fish and the object during exploration were extracted (custom made Matlab routines) and examined in terms of potential sensory related behavior such as object approaching trajectories, the EOD frequency or the occurrence of novelty responses.

We further use the kinematic data to model the electric images associated with each EOD. This enables us to study electric image dynamics related to posture and sensing behavior of the animal. Quantifying the change between successive electric images, the motor strategies used by the fish during object exploration can be related to their impact on the electrosensory information flow. Thus this is the first study considering the impact of electrolocation behavior on sensory information in a temporal and context-dependent manner.


II. Electrophysiological recordings of both single cells and simultaneous recordings of multiple neighbouring cells in the topographically arranged ELL

In the second phase of this project we will concentrate on the neuronal representation and information extraction of electrical images at the level of the electrosensory lateral-line lobe.

The responsiveness of ELL neurons will be investigated in response to defined objects presented at fixed variable distances in the neurons receptive field. Moreover a dynamic manipulation of the object position in relation to the receptive field will be performed to simulate object exploration behavior. The neuronal responses will be analyzed using standard rate-coding and time-coding approaches, with the aim to investigate the range to which objects may be detected by single neurons and describe the dynamic discharge behavior during artificial object exploration. Following a novel approach in this field of research the data are analyzed using ROC analysis.

This then will be related to the corresponding D-parameters calculated for behavioral and modeling data. With this we will be able to compare the neuronal results to the behavioral and modeled data to investigate if and how the sensory flow which is available to fish during object exploration is used to advance active electrolocation.