Rhythmic Activity in a Forebrain Vocal Control NucleusIn Vitro

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Abstract
The learned vocalizations of songbirds constitute a rhythmic behavior that is thought to be governed by a central pattern generator and that is accompanied by highly patterned neural activity. Phasic premotor activity is observed during singing in HVC [used as a proper name following the nomenclature of Reiner et al. (2004)], a telencephalic song system nucleus that is essential for song production. Moreover, HVC neurons display phasic patterns of auditory activity in response to song stimulation. To address the cellular basis of pattern generation in HVC, we investigated its rhythm-generating abilities.We report here the induction of sustained, rhythmic activity patterns in HVC when isolatedin vitro. Brief, high-frequency stimulation evoked repetitive postsynaptic potentials (PSPs) and local field potentials (LFPs) from HVC neurons recorded in a brain slice preparation made from adult male zebra finches. These rhythmic events were sustained for seconds in the absence of ongoing, phasic stimulation, and they had temporal properties similar to those of syllable occurrence within zebra finch song. Paired recordings revealed synchrony between repetitive PSP and LFP occurrence, indicating that a population of cells participates in this patterned activity. The PSPs resulted from multiple, coordinated, fast-glutamatergic, synaptic inputs. Moreover, their occurrence and timing relied on inhibitory synaptic transmission. Thus, HVC itself has rhythmic abilities that could influence the timing of neural activity over relatively long time windows. These rhythmic properties may contribute to song production or perceptionin vivo.