Figure 1.

Electrosensory circuitry and natural stimuli. (A) Peripheral electrosensory afferents (EAs) enter the hindbrain at the deep fiber layer (DFL) of the electrosensory lateral line lobe (ELL) and project onto two types of pyramidal neurons (ON: green; OFF: magenta) within the pyramidal cell layer (PCL). ON type cells have a basilar dendrite that connects directly to the EAs, while OFF type cells lack such a basilar dendrite and instead receive disynaptic input via local interneurons (G) within the granule cell layer (GCL). The apical dendrites of both types extend through the stratum tractus fibrosum (StF) to the molecular layers of the ELL (VML, ventral molecular layer; DML, dorsal molecular layer). Both types of neurons send projections to higher brain areas, such as the midbrain torus semicircularis (TS). (B) Left: the electric organ discharges (EODs) of two fish (green and blue) interfere and thus create a sinusoidal beat (cyan) whose frequency is equal to the EOD frequency difference between the two fish. Right: during an electro-communication call (i.e., a chirp), the emitter fish’s EOD frequency (top green trace) transiently increases for a brief period of time (top orange trace), while the receiver fish’s EOD frequency (top blue trace) remains constant. The chirp results in a phase reset of the beat (bottom brown trace). (C) Left: EOD waveform from Apteronotus leptorhynchus (black) with amplitude modulation (AM, cyan) and envelope (purple) waveforms. We note that the envelope corresponds to the depth of modulation of the EOD AM that is due to relative movement (dashed gray line) between individuals. Right: shown are the frequency contents of the full signal (black), the AM (cyan), and the envelope (purple). (D) EOD AM (cyan) originating from an object (orange) that is moving along the fish’s body (dashed orange arrows) and the corresponding electric image projected onto the skin (cyan).