Two modes of information processing in the electrosensory system of the paddlefish (Polyodon spathula)
Paddlefish are uniquely adapted for the detection of their prey, small water fleas, by primarily using their passive electrosensory system. In a recent anatomical study, we found two populations of secondary neurons in the electrosensory hind brain area (dorsal octavolateral nucleus, DON). Cells in the anterior DON project to the contralateral tectum, whereas cells in the posterior DON project bilaterally to the torus semicircularis and lateral mesencephalic nucleus. In this study, we investigated the properties of both populations and found that they form two physiologically different populations. Cells in the posterior DON are about one order of magnitude more sensitive and respond better to stimuli with lower frequency content than anterior cells. The posterior cells are, therefore, better suited to detect distant prey represented by low-amplitude signals at the receptors, along with a lower frequency spectrum, whereas cells in the anterior DON may only be able to sense nearby prey. This suggests the existence of two distinct channels for electrosensory information processing: one for proximal signals via the anterior DON and one for distant stimuli via the posterior DON with the sensory input fed into the appropriate ascending channels based on the relative sensitivity of both cell populations.