Midbrain electrosensory processing in a mormyrid fish: multimodal integration, recurrent feedback, and cerebellar influence

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Our ability to perceive, move, think, and remember arises from interactions between networks of neurons in the brain. Neuroscience research seeks to understand such interactions. However, in many cases, progress has been slow because the parts list is too long and the parts themselves are too complex. This project takes advantage of an unusual animal--a fish that emits its own electrical field, in which the individual brain structures are sufficiently simple and well-studied that their interactions can be understood in great detail. Specific goals of this project are to define the function of feedback or "backward" connections from higher to lower stages of sensory processing as well as the function of connections between the cerebellum and sensory processing regions. Feedback and cerebellar connections are believed to be critical for sensory processing in humans and have been implicated in neurological disorders such as autism, but our knowledge is sketchy and insufficient or designing treatments. By providing detailed information about such interactions in a simpler system, this project will serve as a foundation for understanding interactions in more complex systems such as the human brain. The investigator will use the resources developed from this project's research activities to improve science literacy and education regionally, nationally, and internationally. By virtue of their tractable electrosensory and electromotor systems mormyrid fish have proven to be a valuable model system for linking structure and function in neural circuits. Studies of the first processing stage for the electrosense in the electrosensory lobe (ELL) have produced a fairly complete and well-tested model in which an experimentally measured form of spike timing-dependent synaptic plasticity acts on well-described motor corollary discharge responses to predict and cancel out self-generated sensory inputs. Anatomical studies have mapped central electrosensory pathways and behavioral studies have documented sophisticated electrolocation abilities that likely depend on higher-level neural processing. However physiological studies of higher stages of electrosensory processing are needed to link structure and function. The goal of this project is to provide the first in depth characterization of the midbrain lateral toral nucleus (NL)--the next major processing stage after ELL. The investigators' approach will include intracellular and extracellular electrophysiology in awake preparations, simultaneous behavioral measurements, and circuit manipulations. Proposed experiments will test specific hypotheses regarding NL function while at the same time addressing a number of general issues in neuroscience including multimodal integration, functions of recurrent feedback, and roles of the cerebellum in sensory processing.