Research on how the brain learns and remembers is crucial to basic science and to our society?s efforts to understand and treat learning disabilities and memory loss. One productive line of research has been the study of eyeblink conditioning, which shows a strong correspondence between humans and other animals in the brain structures and mechanisms involved. The hippocampus is a critical brain structure shared by all mammals that, if damaged, devastates long term declarative memory. Two patterns of hippocampal cellular activity are especially relevant local field potentials (3-7 Hz slow wave or EEG oscillations known as theta) and the action potentials of output neurons that convey the results of hippocampal calculations to other target structures in the brain. Theta rhythm is known to predict how fast conditioning will occur in rabbits and there are recent findings that it is related to human memory as well. This project uses a unique brain-computer interface that controls whether theta is present or absent during training without the need for drugs or other invasive treatments. Such training during theta is 2 to 4 times faster than nontheta. Recording from single hippocampal neurons, investigators expect to characterize the hippocampal output message to target structures and to determine how and why the message is optimal during theta. Projected results include significantly different response profiles of output neurons between theta and nontheta states, with a diverse population of interneurons related to different aspects of theta. These will be examined with respect to the improvement or impairment of behavioral learning and will clarify how the hippocampus contributes to memory. Such findings, as well as the participation of graduate and undergraduate students, suggest a broad impact of this project on scientific inquiry, student education, and the important social problem of memory impairment.