Cellular basis for the processing of acoustic information in the mammalian cochlear nuclei
Hearing tells us what is going on and where it happens. The ears only give us a running measure of the spectral content of sounds; where sounds arise and what they mean has to be computed by the brain. The effortlessness with which mammals perform this task disguises the feats that are performed. It is our goal to understand how neurons in the cochlear nuclear complex, the part of the brain that receives input from the ear from the auditory nerve, begin these computations and how these neuronal networks are altered by the loss of hearing.
We explore these questions by making electrophysiological recordings in vitro. The illustration (below) shows that the cochlear nuclear complex comprises an unlayered ventral cochlear nucleus and a layered dorsal cochlear nucleus whose circuits resemble the adjacent cerebellum. The properties of synapses and the biophysical properties of differ dramatically between neurons in the two regions. Synapses in the ventral cochlear nucleus show little plasticity and act on neurons that preserve the information contained in the timing of firing. Synapses in the outermost layer of the dorsal cochlear nucleus in contrast, are weakened or strengthened by coordinated activity. In mutant mice, the function of these neuronal circuits is altered. We are using mutant mice to learn how these neuronal networks change in animals.
In the cochlear nuclei we address questions at several different levels. At the cellular and molecular levels we seek to understand how synaptic function and biophysical properties of neurons are regulated. At the systems level we want to understand how the brain begins to extract information about the location and meaning of sounds. We also seek to gain a better understanding of how hearing loss affects the function of the neuronal networks in the cochlear nuclei.