Electrosensory processing inApteronotus albifrons: implications for general and specific neural coding strategies across wave-type weakly electric fish species

Abstract

Understanding how the brain processes sensory input to generate behavior remains an important problem in neuroscience. Towards this end, it is useful to compare results obtained across multiple species to gain understanding as to the general principles of neural coding. Here we investigated hindbrain pyramidal cell activity in the weakly electric fish Apteronotus albifrons. We found strong heterogeneities when looking at baseline activity. Additionally, ON-and OFF-type cells responded to increases and decreases of sinusoidal and noise stimuli, respectively. While both cell types displayed band-pass tuning, OFF-type cells were more broadly tuned than their ON-type counterparts. The observed heterogeneities in baseline activity as well as the greater broadband tuning of OFF-type cells were both similar to those previously reported in other weakly electric fish species, suggesting that they constitute general features of sensory processing. However, we found that peak tuning occurred at frequencies ~15 Hz in A. albifrons, which is much lower than values reported in the closely related species Apteronotus leptorhynchus and the more distantly related species Eigenmannia virescens. In response to stimuli with time-varying amplitude (i.e., envelope), ON-and OFF-type cells displayed similar high-pass tuning curves characteristic of fractional differentiation and possibly indicate optimized coding. These tuning curves were qualitatively similar to those of pyramidal cells in the closely related species A. leptorhynchus. In conclusion, comparison between our and previous results reveals general and species-specific neural coding strategies. We hypothesize that differences in coding strategies, when observed, result from different stimulus distributions in the natural/social environment. CIHR Author Manuscript CIHR Author Manuscript CIHR Author ManuscriptOne of the main goals of neuroscience is to understand how sensory input is processed to give rise to behavior (i.e., the neural code). Towards this end, it has proven useful to compare the neural coding strategies across species to distinguish those that can be generalized from those that are species specific (Brenowitz and Zakon 2015;Carlson 2012;Hale 2014).Weakly electric fishes generate an electric field around their body through the electric organ discharge (EOD) and rely on perturbations of this field generated by objects in the surrounding water to gain information about their environment (Bullock et al. 2005). They consist of diverse families with hundreds of species (Caputi et al. 2005). Interestingly, electric field generation evolved independently in two clades found in South America (Gymnotoidei) and Africa (Mormyroidea) (Bennett 1971). While recent studies have identified general and species-specific neural coding strategies by quantitatively comparing neural responses across several stages of sensory processing in several mormyriform species whose EODs consist of sequences of species-specific stereotyped pulses separated by quiescence (Baker et al. 2...

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“…Maximum phase locking also peaks at low frequencies ( Fig 4B). These values closely match previously reported values (Martinez et al, 2016). Temporal coding accuracy is conveniently quantified using random noise stimuli and information theory (Borst and Theunissen, 1999).…”

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