Background on neuronal tracing
A key aspect to understanding the brain’s function is knowing its architecture, in particular the connections between different brain regions. For example, communication between the hippocampus and the prefrontal cortex brain regions is involved in the formation of episodic memory, a special type of memory which includes autobiographical events (see Jin & Maren, 2015). Directional flow of information between different parts of the brain is mediated via individual neurons. Neurons are composed of a cell body, with dendrites receiving incoming information, and a projecting axon sending information onwards to other neuronal cells. Synapses at the terminals of axons form connections to dendrites of proximal neuronal cells. In the specific example of episodic memory, a subset of hippocampal neurons projects axons directly to the prefrontal cortex, but also indirectly via synapses to neurons in other brain regions. Further, the connections between regions are often reciprocal, forming a neuronal loop which is activated and strengthened during memory formation and memory retrieval.