The first article discusses the gymnotiform fish Eigenmannia, a weakly electric fish, which generates a weakly electric signals for electrolocation and communication. Metzner provides explanation as to how the signals are produced and mentions the electric organ discharges (EODs) that are driven by a medullary pacemaker nucleus. The electrolocation can suffer from dramatic degradation when the conspecifics with a similar frequency are present in the environment. To avoid jamming, Eigenmannia modulates its EOD frequency depending upon the neighbor’s frequency. If the neighbor’s frequency is lower, the fish increases its frequency and if it is higher, there is a subsequent lowering of the frequency observered. Metzner cites Bullock et al referring to the phenomenon as Jamming Avoidance Response and presents the possible control center for JAR. The feature-extracting neurons present in the diencephalic prepacemaker nucleus (PPn-G), lying medially, are the units that …show more content…
These neurons are excited in response to lower jamming frequencies, increasing the frequency of the fish higher whereas they get inhibited by higher jamming frequencies, producing a discharge deceleration. However, Metzner found different a mechanism for the motor control of the JAR from the one described previously. The involvement of two prepacemaker nuclei, one PPn-G and one sublemniscal prepacemaker nucleus (SPPn) and their effect on JAR was observed by lesion study. Article provides multiple pharmacological experiments to elucidate the transmitter types involved. The results suggest a different hypothesis that the JAR is controlled by two separate motor pathways. One controlling rise in frequency originates in the dorsal substructure of the nucleus