Passive Electroreception

• Electrosensing is common in aquatic organisms due to water's low electrical resistance.
• Passive electroreception is more prevalent than active.
• All living beings generate a bioelectric field detectable by animals for purposes like finding prey, avoiding predators, and sensing the environment.

Passive Electroreception

• Ampullary electroreceptors facilitate passive electroreception, where impulses travel through a canal, stimulating nerve signals to the brain.
• Ampullae of Lorenzini detect voltage variations, creating electrical potential across membranes.
• Sharks have many pores on their heads with canals, enhancing sensory reception with shorter brain pathways.
• Passive electroreception functions primarily in prey detection, identifying conspecifics, and detecting predators.
• It might also be involved in navigation via magnetism, though evidence remains inconclusive.
• Passive electroreception relies on external electric fields, whereas active involves generating them.
• Bioelectric fields from muscle contractions and external sources (lightning, cables) are detected.
• Ampullary electroreceptors like Ampullae of Lorenzini are crucial, embryologically originating from lateral line mechanoreceptors.
• Sensory transduction occurs as external electric fields create small voltages across membranes, triggering calcium channels, neurotransmitter release, and nerve firing.

Case Studies of Passive Electroreception

• Platypuses use three electroreceptor types in their bill skin, mainly mucous gland receptors, functioning like antennas.
• Guiana dolphins utilize vibrissal crypts, ampullary receptors innervated by the trigeminal nerve.
• Passive electroreception evolved uniquely in fish, monotremes, and some cetaceans, showing convergent evolution with varied anatomical origins.
• Hammerhead sharks have heads shaped to maximize receptor distribution.
• Elephant nose fish use two fovea, one nasal and one on a moveable chin appendage, possibly to identify food.
• Dolphins sense electricity through pores in vibrissal crypts; transduction mechanisms are similar to platypuses.

Active Electroreception

• Active electroreception involves generating electric fields via modified muscle or nerve cells and perceiving distortions to detect objects for navigation and communication.
• It evolved independently in Mormyriformes (mormyrids) and Gymnotiformes (gymnotids).
• Electric organs emit electric organ discharges (EODs) produced by electrocytes controlled by a pacemaker nucleus.
• Wave signals are continuous and used for spatial resolution, while pulse signals are intermittent and used for recognition and communication.
• Specialized electroreceptors include mormyromasts/gymnomasts, which measure stimulus intensity and spatial data.
• Also the knollenorgans, which are time coders crucial for electrocommunication.
• The ampullary receptors carry out low-frequency passive electrolocation.
• Electric imaging involves creating electric "images" of nearby objects via distortions in the electric field, affected by size, distance, resistance, capacitance, and shape.
• EOD waveform and interval patterns transmit details about species, sex, and social interactions.
• Animals use electric imaging, electrocommunication, noise reduction, and adaptive filtering.

Electric Organ Discharge and Noise Reduction

• Weakly electric fish adjust their EOD frequency to avoid signal interference from conspecifics, a mechanism known as Jamming Avoidance Response (JAR).
• The JAR involves distributed comparisons of amplitude and phase beat patterns.
• Corollary discharge mechanisms suppress a fish's perception of its own EOD to better detect signals from others.
• Electric Organ Corollary Discharge (EOCD) predicts sensory consequences of self-generated EODs, differentiating external stimuli from self-induced noise.
• Electric sensory information is often integrated with mechanosensory information for a comprehensive understanding of the environment.
• Sensory neurons are overrepresented in specific areas like the nose appendage, allowing complex information processing in 3D environments.
• Conductor and non-conductor materials affect the electric field differently aiding in object discrimination.
• Animals can perceive cubes at larger distances than spheres due to the properties of objects and the use of movement to interrogate 3D shapes and differentiate from a distance.
• Knollenorgan receptors are time coders used to identify mates.
• The active electric sense is prioritized over vision, but animals can transfer information between systems.
• Gymnotids are shoaling fish that need to increase or decrease discharges to communicate.