I am having a bit of an issue with my intuitive understanding of Ketamine's newfound role in treating depression. It is my understanding that Ketamine works by allowing synaptogenesis. The evidence for this mechanism seems to be quite robust. However, it leaves me with a nagging question. Why would excessive pruning of synapses lead primarily to symptoms of sadness? It would seem to me that issues with synaptogenesis would lead primarily to dysfunction of learning, memory, sensory, and decision making, and not be limited primarily to mood.
What am I missing here? Why would a lack of synaptogenesis lead to depression?