Figure 1.

Synaptic organization of cerebellum-like structures in mormyrid fish. (A) Simplified circuit of electrosensory lateral line lobe (ELL) used for modeling of the passive electrosensory system. Parallel fibers originate in the eminentia granularis posterior (EGp) and synapse onto the apical dendrites of medium ganglion (MG) cell with excitatory synapses (bar terminals) and inhibitory stellate cells (St) synapse in the same layer with inhibitory synapses (disk terminals). The parallel fibers carry a sequence of delayed inputs that convey the timing of the EOD command. The Purkinje-like MG cell cancels expected electrosensory signals with an STDP mechanism at the synapse from parallel fibers and stellate cells. Arrows represent the flow of information and mixed inputs. (B) ELL circuitry for the active electrosensory system. Mormyromast electroreceptors transform the field intensity at the skin into a spike latency code that is transformed into a spike burst duration code by deep granular cells (g) controlled by centrally generated corollary discharge input from the juxtalobar nucleus. The electrosensory signal is then transferred to the adaptive stage of electrosensory processing (type-1 medium ganglion (MG₁) and large fusiform (LF) cells), and the expected sensory responses are subtracted. Recurrent connections, modulated by higher centers (preeminential nucleus, PE), are hypothesized to control the threshold of back-propagating broad (dendritic) spikes in MG₁ cells.