Classic observations suggest that the cerebellum is involved in affect and its expression. The neural substrate that mediates this behavior has been unclear. Recently, Sacchetti and his colleagues demonstrated that lesions involving portions of lobules V and VI in the rat cerebellar vermis abolish the consolidation of fear conditioning (Sacchetti et al., 2002). To gain some insight into the circuitry that mediates this effect, we used retrograde transneuronal transport of rabies virus (RV) to examine inputs to and outputs from vermal lobule VI. We found that the cingulate cortex (Cg) is the origin of a substantial disynaptic projection to lobule VI. In addition, we found that the fastigial nucleus and portions of vermal lobule VI are the origin of substantial disynaptic and trisynaptic projections to Cg. These observations suggest that a closed-loop circuit exists between vermal lobule VI and Cg. Furthermore, our results raise the possibility that aspects of fear conditioning, in particular, and emotion, in general may be influenced by this cerebro-cerebellar circuit
