| The mammalian dorsal cochlear nucleus (DCN), with a cerebellum-like organization, receives auditory and non-auditory inputs. Experiments on decerebrate gerbils, allow neuron (unit) recordings without anesthesia. Feedback projections from rostral centers, however, are severed in decerebrate preparations, bringing into question the validity of neural data recorded in decerebrate preparations. In awake preparations, the DCN's neural circuitry is intact, and the animal is more natural. Recordings from awake preparations, especially from the DCN, are rare because of technical difficulties. By combining techniques of survival surgery, and conditioning, with electrophysiological techniques, it was possible to record DCN-unit responses in conscious, awake gerbils ( Merionus unguiculatus). Response maps (RMs), post-stimulus time histograms (PSTHs), responses to notch noise stimuli, and spectro-temporal receptive fields (STRFs) were recorded while gerbils were awake. Some aspects of the units' responses were compared to those from previous experiments in anesthetized and decerebrate gerbil preparations. Of 102 units recorded, all RM types observed in decerebrate gerbils were also observed in the awake gerbil, with the notable exception of type IV units. Type III units were still the most commonly recorded gerbil DCN unit. The percentage of type I/III units recorded in the awake prep was significantly higher than in decerebrate gerbils. No significant changes were observed in either RM shape or notch noise responses. Although most awake DCN units had spontaneous activity (typically less than 20 spikes/s), these rates were lower than those in decerebrate gerbils. DCN neurons may be more inhibited in awake, than in decerebrate gerbils. Different unit types seem to respond slightly differently to notch noise stimuli. For example, type III units were most sensitive to spectral notches. Finally, DCN unit STRFs were estimated using responses to ripple noise (RN) and dynamic moving ripple (DMR). STRFs of type I/III, II, III, and III-i units showed a tuned excitatory area to the unit's best frequency. An inhibitory area, located near the excitatory area, was observed in both type III and III-i units. STRFs of type IV-i units cannot be estimated because the units are inhibited by these stimuli. The STRF data are new; no such data from decerebrate gerbils exist. |
