Oscillatory and burst discharge in the apteronotid electrosensory lateral line lobe

Abstract

Oscillatory and burst discharge is recognized as a key element of signal processing from the level of receptor to cortical output cells in most sensory systems. The relevance of this activity for electrosensory processing has become increasingly apparent for cells in the electrosensory lateral line lobe (ELL) of gymnotiform weakly electric fish. Burst discharge by ELL pyramidal cells can be recorded in vivo and has been directly associated with feature extraction of electrosensory input. In vivo recordings have also shown that pyramidal cells are differentially tuned to the frequency of amplitude modulations across three ELL topographic maps of electroreceptor distribution. Pyramidal cell recordings in vitro reveal two forms of oscillatory discharge with properties consistent with pyramidal cell frequency tuning in vivo. One is a slow oscillation of spike discharge arising from local circuit interactions that exhibits marked changes in several properties across the sensory maps. The second is a fast, intrinsic form of burst discharge that incorporates a newly recognized interaction between somatic and dendritic membranes. These findings suggest that a differential regulation of oscillatory discharge properties across sensory maps may underlie frequency tuning in the ELL and influence feature extraction in vivo.