Sixth sense: How the black ghost knifefish detects weak electrical signals
Researchers from the Universities of Ottawa, Canada, and Bielefeld, Germany have started to understand how sensory systems achieve exceptionally high sensitivities to information about the environment.
The sensory systems of vertebrates are designed to allow animals to experience their surroundings and changes occurring within it. By integrating all the relevant information, they are able to alter the animal’s behavioural performance and aid their survival. How these systems exhibit the high sensitivities required is a question that neuroscientists are yet to answer.
In a study published in the Journal of Neurophysiology, a team of biologists led by Professor Leonard Maler has begun to explain the phenomenon of how the nervous system achieves high levels of sensitivity using the weakly electric fish Apteronotus albifrons (the black ghost knifefish).
Apteronotus use their electrosense to identify prey by generating an electrical field with their electrical organ discharge (EOD). Disruptions to this field, with electrical signals as small as 1 µV and a sensory integration time of less than 200 ms, are detected by the electrosensory lobe (ELL) located in the hindbrain. How these signals are detected and amplified by the fish’s nervous system was, until recently, not well understood.
To investigate, lead author Dr Sarah Jung studied the first electrosensory processing steps: the primary electrosensory afferents (EAs) and the pyramidal cells (PCs) of the ELL.
Previous data shows that the firing rates of afferent spike trains are not noticeably modulated by minimal prey-like signals. However, in the ELL even very weak stimuli increase the spike count of PCs. This suggests that a spike timing/pattern code may be transformed into a rate code where an EA and PC meet.
The PCs project to a brain region called the torus semicircularis (TS) whose neurons can respond to prey stimulation. By modelling the TS and the input it receives from the previously recorded PCs, the researchers found that the TS can extract information close to the limits of previously monitored behavioural performance.
Electrodes were placed through the hindbrain of the sample using Scientifica’s IVM Triple, a three-axis motorised micromanipulator specifically designed for in vivo experiments.
Jung S.N., Longtin A., Maler L. Weak signal amplification and detection by higher-order sensory neurons Journal of Neurophysiology (2016) doi: 10.1152/jn.00811.2015
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