Electrosensory Brain Stem Neurons Compute the Time Derivative of Electric Fields in the Paddlefish

Abstract

For many aquatic animals, the electrosense is an important sensory system used to detect prey or conspecifics at short to medium range and for long-range orientation. Passive electroreceptive animals sense the minute electric fields of animate and inanimate sources and it has been thought that they are most sensitive to sources that modulate the field around a few Hertz. Our data on the properties of the electrosensory system in the paddlefish reveal that the firing rate of electrosensory brain stem neurons represents the first derivative of the stimulus, i.e. the rate of change in intensity of an electric field. Furthermore, the responses to several non-periodic stimuli suggest that the electrosensory system monitors changes in field intensity caused by the relative movement between source and receiver and converts spatial field structure into its time derivative form. This new interpretation solves a number of contradictions between behavioural observations and electrophysiological studies on the electrosensory system of vertebrates.

Edge-Detection Filter Improves Spatial Resolution in the Electrosensory System of the Paddlefish

“…The modulation voltage Vmod is determined by the level of transmitter released from primary afferent fibers innervating the DON unit. The filter properties of primary afferent fibers and DON units are well known and can be estimated as a derivative filter with an additional low-pass filter Hofmann et al 2004). Therefore we differentiated the calculated field strength at the receptor and applied a low-pass filter (Igor Filter Design Lab, MPR low-pass filter: endpass band, 7 Hz; start stop-band, 18 Hz; 10 dB, 31 Terms, error 0.501).…”

“…Therefore we differentiated the calculated field strength at the receptor and applied a low-pass filter (Igor Filter Design Lab, MPR low-pass filter: endpass band, 7 Hz; start stop-band, 18 Hz; 10 dB, 31 Terms, error 0.501). The low-pass filter parameters were chosen to match the frequency response of DON units (Hofmann et al 2004). This signal was then used as Vmod to modulate the integrate-and-fire model.…”

Response properties of electrosensory units in the midbrain tectum of the paddlefish (Polyodon spathula Walbaum)

“…But, why do peripheral neurons attenuate frequencies that are obviously relevant for the animal? It is known that the filter curve for peripheral units can be described as a first derivative with an additional low-pass filter (Hofmann et al, 2004). In the special case of a sine wave, a derivative filter would attenuate lower frequencies and shift the phase of the signal, but would not change the waveform.…”

“…The physiology of the electrosensory system has been extensively studied in primary afferent fibers (Wojtenek et al, 2001), and at the level of the hindbrain DON (Hofmann et al, 2004;. In this study, we analyzed the response properties of tectal units for comparison with primary afferents and DON units.…”

Response properties of the electrosensory neurons in hindbrain of the white sturgeon, Acipenser transmontanus

“…The dermal electroreceptor has also been described in sturgeon and paddlefish [6,7] , and the processing of electrosensory information in paddlefish has been elucidated [8,9] . However, due to the differences in body type and feeding habits, the mechanism of electrosensory processing in sturgeon remains unknown.…”