Sense and Sensitivity: Spatial Structure of conspecific signals during social interaction

Organisms rely on sensory systems to gather information about their environment. Localizing the source of a signal is key in guiding the behavior of the animal successfully. Localization mechanisms must cope with the challenges of representing the spatial information of weak, noisy signals. In this dissertation, I investigate the spatial dynamics of natural stimuli and explore how the electrosensory system of weakly electric fish encodes these realistic spatial signals. To do so In Chapter 2, I develop a model that examines the strength of the signal as it reaches the sensory array and simulates the responses of the receptors. The results demonstrate that beyond distances of 20 cm, the signal strength is only a fraction of the self-generated signal, often measuring less than a few percent. Chapter 2 also focuses on modeling a heterogeneous population of receptors to gain insights into the encoding of the spatial signal perceived by the fish. The findings reveal a significant decrease in signal detection beyond 40 cm, with a corresponding decrease in localization accuracy at 30 cm. Additionally, I investigate the impact of receptor density differences between the front and back on both signal detection and resolution accuracy. In Chapter 3, I analyze distinct movement patterns observed during agonistic encounters and their correlation with the estimated range of receptor sensitivity. Furthermore, I uncover that these agonistic interactions follow a classical pattern of cumulative assessment of competitors\u27 abilities. The outcome of this research is a comprehensive understanding of the spatial dynamics of social interactions and how this information is captured by the sensory system. Moreover, the research contributed to the development of a range of tools and models that will play crucial roles in future investigations of sensory processing within this system

Spatial processing of conspecific signals in weakly electric fish: from sensory image to neural population coding

In this dissertation, I examine how an animal’s nervous system encodes spatially realistic conspecific signals in their environment and how the encoding mechanisms support behavioral sensitivity. I begin by modeling changes in the electrosensory signals exchanged by weakly electric fish in a social context. During this behavior, I estimate how the spatial structure of conspecific stimuli influences sensory responses at the electroreceptive periphery. I then quantify how space is represented in the hindbrain, specifically in the primary sensory area called the electrosensory lateral line lobe. I show that behavioral sensitivity is influenced by the heterogeneous properties of the pyramidal cell population. I further demonstrate that this heterogeneity serves to start segregating spatial and temporal information early in the sensory pathway. Lastly, I characterize the accuracy of spatial coding in this network and predict the role of network elements, such as correlated noise and feedback, in shaping the spatial information. My research provides a comprehensive understanding of spatial coding in the first stages of sensory processing in this system and allows us to better understand how network dynamics shape coding accuracy

From Perception to Cognition: Multisensory object recognition and navigation in the weakly electric fish <em>Gnathonemus petersii</em>

Within a multisensory system, individual senses can interact in several beneficial ways increasing the reliability and flexibility of the multisensory percept. Such a multisensory system is found in the African weakly electric fish Gnathonemus petersii , which uses active electrolocation and a specialised visual system for the perception of its environment. Additionally, these fish possess a mechanosensory lateral line system, which, however, has been scarcely investigated. In this thesis I used two behavioural paradigms, object recognition and navigation, as well as anatomical methods to investigate how the sensory systems of G. petersii operate together and how multisensory information is processed. The results during object recognition show that G. petersii is capable of spontaneous cross-modal object recognition, a highly cognitive ability previously known only in a few mammalian species, during which object related information can be transferred between senses and used for object recognition in a flexible manner. Furthermore, I found that these fish process multisensory information similarly to mammals, by using dynamic weighting of sensory inputs. The anatomical studies of the mechanosensory lateral line system additionally show a reduction of the peripheral lateral line system, explaining why the lateral line system was not involved in object recognition during my experiments. In the second part of my thesis the results of the navigational experiments show that G. petersii uses an egocentric strategy aided by visual landmarks for navigation in a familiar environment and is able to use cross-modal landmark recognition to fulfil the task. In conclusion, the results of my thesis show that the multisensory system of G. petersii optimally exploits the advantages of possessing multiple senses, which provide similar information on different spatial scales and provide new insights into the mechanisms underlying multisensory processing in non-mammalian vertebrates

Electric Imaging through Evolution, a Modeling Study of Commonalities and Differences

<div><p>Modeling the electric field and images in electric fish contributes to a better understanding of the pre-receptor conditioning of electric images. Although the boundary element method has been very successful for calculating images and fields, complex electric organ discharges pose a challenge for active electroreception modeling. We have previously developed a direct method for calculating electric images which takes into account the structure and physiology of the electric organ as well as the geometry and resistivity of fish tissues. The present article reports a general application of our simulator for studying electric images in electric fish with heterogeneous, extended electric organs. We studied three species of Gymnotiformes, including both wave-type (<i>Apteronotus albifrons</i>) and pulse-type <i>(Gymnotus obscurus</i> and <i>Gymnotus coropinae</i>) fish, with electric organs of different complexity. The results are compared with the African (<i>Gnathonemus petersii</i>) and American (<i>Gymnotus omarorum</i>) electric fish studied previously. We address the following issues: 1) how to calculate equivalent source distributions based on experimental measurements, 2) how the complexity of the electric organ discharge determines the features of the electric field and 3) how the basal field determines the characteristics of electric images. Our findings allow us to generalize the hypothesis (previously posed for <i>G. omarorum</i>) in which the perioral region and the rest of the body play different sensory roles. While the “electrosensory fovea” appears suitable for exploring objects in detail, the rest of the body is likened to a “peripheral retina” for detecting the presence and movement of surrounding objects. We discuss the commonalities and differences between species. Compared to African species, American electric fish show a weaker field. This feature, derived from the complexity of distributed electric organs, may endow Gymnotiformes with the ability to emit site-specific signals to be detected in the short range by a conspecific and the possibility to evolve predator avoidance strategies.</p></div