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I thought I would make this a reply since I examined another article on corollary discharge in crickets.

As we have learned in class, proprioceptors continually update our nervous system with sensory information on changes in the body, constituting part of the “reafferent loop” of our nervous system.  However, there is a risk that these internally generated signals may become confused with sensory information from external stimuli, or they may desensitize an animal’s sensory pathways.  In order to prevent this, corollary discharges are sent to sensory regions and tell the nervous system to ignore the self-generated sensory feedback.  This is similar to the activity in which we watched our fingers move but noticed no movement in the background.  Corollary discharge influences and fine-tunes how we interpret sensory information.

The question, then, is what cells mediate this activity?  Through studying crickets, James Poulet and Berthold Hedwig have found a single type of interneuron is responsible for the pre- and postsynaptic inhibition of the auditory sensory neurons in crickets when they sing (1).  Why crickets?  Crickets hear with their forelegs and generate song with their wings, and the whole time while singing, they are fully sensitive to auditory input (1).  There must then be some neurons along the prioprioceptive and auditory pathways that mediate the inputs received by the CNS during song production that allow the cricket to maintain full sensitivity to auditory input, and this is accomplished with corollary discharge.

The cell responsible is known as a corollary discharge interneuron, CDI.  Poulet and Hedwig outline three major structural properties of CDIs that allow them to operate as they do.  First, the cell body/dendrites are located in the mesothoracic ganglion, which allows the cell to receive input from the singing CPG.  Second, the axonal branching overlaps with the auditory neuropil (gray matter) in the prothoracic ganglion in such a way so as to allow for direct synaptic output to auditory neurons.  Third, the axon also extends to various are of the CNS and could therefore affect the other sensory pathways involved with singing.

It was observed that the CDIs would fire synchronously with wing-closing motor activity (song production) and auditory inhibition.  I won’t discuss the experiments, but the results suggest that CDIs are both necessary and sufficient for mediation of corollary discharge during singing.  If you’d like more detail, a link to the article is provided below.

I just thought this article was interesting as it gives some beginning insight to the molecular basis of corollary discharge.  The article was from January of 2006, and I imagine there is still much to learn about the cells acting behind corollary discharge.

1. http://www.sciencemag.org/cgi/content/full/311/5760/518