RT Journal Article SR Electronic T1 Effects of Hippocampal State-Contingent Trial Presentation on Hippocampus-Dependent Nonspatial Classical Conditioning and Extinction JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 6003 OP 6010 DO 10.1523/JNEUROSCI.4859-13.2014 VO 34 IS 17 A1 Miriam S. Nokia A1 Jan Wikgren YR 2014 UL http://www.jneurosci.org/content/34/17/6003.abstract AB Hippocampal local field potentials are characterized by two mutually exclusive states: one characterized by regular θ oscillations (∼4–8 Hz) and the other by irregular sharp-wave ripples. Presenting stimuli during dominant θ oscillations leads to expedited learning, suggesting that θ indexes a state in which encoding is most effective. However, ripple-contingent training also expedites learning, suggesting that any discrete brain state, much like the external context, can affect learning. We trained adult rabbits in trace eyeblink conditioning, a hippocampus-dependent nonspatial task, followed by extinction. Trials were delivered either in the presence or absence of θ or regardless of hippocampal state. Conditioning in the absence of θ led to more animals learning, although learning was slower compared with a yoked control group. Contrary to expectations, conditioning in the presence of θ did not affect learning. However, extinction was expedited both when it was conducted contingent on θ and when it was conducted in a state contrary to that used to trigger trials during conditioning. Strong phase-locking of hippocampal θ-band responses to the conditioned stimulus early on during conditioning predicted good learning. No such connection was observed during extinction. Our results suggest that any consistent hippocampal oscillatory state can potentially be used to regulate learning. However, the effects depend on the specific state and task at hand. Finally, much like the external environment, the ongoing neural state appears to act as a context for learning and memory retrieval.