© Universität Bielefeld
Electroreception
Weakly electric fish actively control the sensory imaging process by "electrically illuminating" their surroundings. This allows them to detect, locate and percive their environment. In addition, they use the same energy cariere (EODs) for communication.
For electrolocation they rely on the subtle modulations of the carrier signal. However, these modulations are subjected to a strong decay with distance to an object and non-linear interaction. Additionally, since the carrier is self-generated, all movements of the animal lead to changes of the carrier. Thus szene-analysis requires to distinguish sensory information embedded in a noisy re-afferent input. We are investigating how electric fish gain detailed sensory information by activly manipulating the carrier properies (e.g.: orienting behaviours and exploratory patterns that focus electric input on specific sensory structures or neuronal processes that extract singularities related to the sensory-motor continuity). Active electrolocation is paradigmatic of Jules Vernes "Mobilis in mobile", making electric fish an ideal model to investigate how perceptual consistence can be achived by correlating motor and sensory actions.
- Active System
We presently have started to investigate the transformation of peripheral sensory images to the first central area (ELL).
Here, information is segregated in at least two channels (amplitude and phase). We want to compare spatial receptive fields of both channels and characterize the information transfer from the periphery to each module. This will allow a quantitative analysis of information transfer in active electrolocation and, by simultaneous recordings of multiple cells, a first understanding of network-effects in real-time.
Additionally we will start to focus on spatio-temporal relations by advancing from the previously static presentation of peripheral stimuli to more naturalistic moving stimuli.
- Passive System
The passive sensory system of Mormyrids is tuned to the electrical signals of other animals as well as to potentials arising from geochemical sources. Applying computational methods we have begun to characterize information transfer by this sensory system. In accordance with data obtained by M. Hofmann on the paddlefish it becomes apparent, that ampullary receptors are tuned to maximize sensitivity for temporally changing DC fields and low frequencies. Thus they are highly sensitive to changes of the field. The exact transfer properties are currently being investigated.In term sof electrolocation our present results indicate that the system might calculate source-distance in the temporal domain.
- Anatomy
In cooperation with Dr. Kirsty Grant we investigate the electrosensory systems anatomy both at the peripheral and the central level. In recent studies we characterised the distribution of the 3 electroreceptors in conjunction with their central representation. We established a strong "cortical" magnification of the Schnauzenorgan and head regions in the ELL (see beside).
In joint anatomical and electrophysiological experiments we investigate the senory integration of A- and B- mormyromasts. These are differently sensitive to phase and amplitude modulations of the electric organ discharge and their information must be integrated to determine the electrical impedance of objects under inspection by the animal. Our data shows that initial steps to enable this are already achived at the level of the ELL.
Presently we started investigating how peripheral excitation patterns are reflected in the first sensory processing stages. We aim to compare the neuronal networks underlying amplitude and phase encoding to better understand how parallel networks enable swift szene-analysis using partially redunant sensory inputs. This project is directly linked to ongoing neurophysiological works.© Universität Bielefeld Extending on the above anatomical studies we have begun to characterize the somatotopic mapping from the ELL to the midbrain torus semicircularis. For an animation of the connectivity, please see the following video:
Our studies have established a topographic map in the torus semicircularis and future research will need to investigate if this map is the basis for the merging of phase and amplitude information.
