Key Points
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First- and second-order contrast stimuli can be described for the visual, auditory and tactile senses. Similarly, electrosensory contrast patterns vary over large spatial and temporal scales.
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Fast exponential adaptation and power law adaptation in electrosensory afferent neurons partition the range of natural electrosensory stimulus frequencies and enable different signal processing goals.
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Comparison of the electrosensory and retinal adaptation algorithms reveals many similarities.
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The electrosensory of ON and OFF ganglion cells can also be compared to retinal ON and OFF ganglion cells. Despite different biophysics and network architectures, these cells share the same algorithmic role for the electrosense and vision. Envelope encoding and decoding mechanisms in the electrosense are related to both locomotion and social behaviours. Both the electrosense and vision combine ON and OFF cell responses to improve the coding efficiency of second-order contrast stimuli.
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Motion reversal triggers switches in electrosensory ON and OFF cell preferences for spatial contrast (polarity), which has also been noted to occur in salamander and mouse retina. Individual ON and OFF cell firing rates encode scalar quantities of motion such as object distance and speed, whereas sequences of population activity encode vector information (motion direction).
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There are many benefits of these flexible coding paradigms for spatiotemporal contrast using ON and OFF cells. It will be important to understand how downstream decoding neurons interpret patterns and sequences of activity of ON and OFF cell populations.
Abstract
To identify and interact with moving objects, including other members of the same species, an animal's nervous system must correctly interpret patterns of contrast in the physical signals (such as light or sound) that it receives from the environment. In weakly electric fish, the motion of objects in the environment and social interactions with other fish create complex patterns of contrast in the electric fields that they produce and detect. These contrast patterns can extend widely over space and time and represent a multitude of relevant features, as is also true for other sensory systems. Mounting evidence suggests that the computational principles underlying contrast coding in electrosensory neural networks are conserved elements of spatiotemporal processing that show strong parallels with the vertebrate visual system.
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Acknowledgements
S.E.C. is supported by a Frederick Banting and Charles Best Canada Graduate Scholarship from the Canadian Institutes of Health Research. A.L. and L.M. are supported by the Natural Sciences and Engineering Research Council of Canada and the Canadian Institutes of Health Research.
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Glossary
- Marr's tri-level hypothesis
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Marr proposed that neural function can be analysed at three levels. The computational level addresses what cognitive problems are solved by a neural process (for example, why should visual scenes be segregated on the basis of local contrast). The algorithmic level describes how computational level elements (such as contours) are represented and manipulated to achieve a computational goal. The physical level describes the biophysical and network implementation of these algorithms.
- Carrier wave
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A high-frequency waveform (often sinusoidal) the amplitude or frequency of which are modulated by an input signa l for the purpose of conveying information to the receiver.
- Envelopes
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Smooth curves outlining the extremes (such as the peaks) of an oscillating carrier signal.
- Sinusoidal AM
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An amplitude modulation in the form of a sine wave.
- High-pass filters
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Filters that pass the components of a signal that are of a higher frequency than a certain cutoff and attenuate signals with frequencies lower than the cutoff frequency.
- Looming
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The situation in which an object moves towards an animal's body, perpendicular to the sensory surface (skin or retina). In visual neuroscience, it specifically refers to the expansion of the retinal image as an object approaches the body.
- Power law relationship
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A functional relationship between two quantities, where one quantity varies as a power (or powers) of another. It can be written as y = tc.
- Receptive field
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A property of sensory neurons that encode spatial information, referring to a particular point on the sensory surface where stimulation alters the rate at which the neuron fires action potentials.
- White noise
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A signal the samples of which can be described as a sequence of serially uncorrelated random values, often drawn from a normal (bell shaped) distribution; the resulting signal contains equal power at all frequencies.
- Half-wave rectification
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A process by which either the positive or negative components of a signal are transmitted. In neurons, the positive (depolarizing) component of an input signal triggers spiking, whereas the hyperpolarizing current does not drive spiking and is thus poorly encoded.
- Low-pass filtering
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A low-pass filter will transmit the low frequencies present in a complex signal, while attenuating its high-frequency components.
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Clarke, S., Longtin, A. & Maler, L. Contrast coding in the electrosensory system: parallels with visual computation. Nat Rev Neurosci 16, 733–744 (2015). https://doi.org/10.1038/nrn4037
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