The identification and manipulation of genes (genetics) has influenced the study of most biological phenomena, including hippocampal learning and memory. The first studies to use genetics to manipulate plasticity and learning in mammals targeted the α -calcium calmodulin-dependent kinase II (α CaMKII) (Silva, Paylor, Wehner, and Tonegawa, 1992a; Silva, Stevens, Tonegawa, and Tang, 1992b) and the tyrosine kinase Fyn (Grant et al., 1992). The results showed that genetic manipulations that disrupt hippocampal synaptic plasticity result in hippocampal-dependent learning deficits. These studies were also influential in starting the new field of molecular and cellular cognition, which combines genetics, neurophysiology, and behavioral neuroscience. What have we learned so far about the hippocampus from this new field, and how successful has this general approach been?

The hippocampus plays a key role in learning and memory. Patients with hippocampal lesions are unable to store new conscious memories, with more severe impairments in recent memories than...