Fig. 1. The early electrosensory pathways. The schematic diagram of the ELL sub-network shows two types of principle neurons, deep (DP) and superficial (P) pyramidal neurons, as well as the primary feedback nuclei, nucleus praeminentialis (nP) and eminentia granularis posterior (EGp). The nP and EGp give rise to the direct feedback pathway (not shown) and the indirect feedback pathway (via parallel fibers), respectively. Feedforward input to these nuclei arises primarily from DP neurons; EGp also receives input from other sensory modalities, such as proprioception. The indirect feedback is indicated by a population of parallel fiber synaptic inputs (numbered 1 to N_f) to the P neuron, and combines direct excitation (solid triangles) with disynaptic inhibition via interneurons I (denoted by open circles). Sensory input is faithfully transmitted to parallel fibers via DP neurons and nP. The dynamics of the parallel fiber synapses then determine the sign of the reafferent image onto P neurons (see Results).