title: Phase-locked hippocampal theta-band responses are related to discriminative eyeblink conditioned responding.
abstract: Hippocampal electrophysiological oscillatory activity is undoubtedly related to learning and memory. The relative power of spontaneously occurring hippocampal theta (∼4-8 Hz) oscillations predicts how fast and how well an animal will learn: more theta predicts faster acquisition of the conditioned response in eyeblink conditioning in both rats and rabbits. Here, our aim was to study how hippocampal theta-band responses to conditioned stimuli elicited during very-long delay discrimination eyeblink conditioning relate to the accompanying conditioned behavior. We trained adult male New Zealand White rabbits using 1500-ms auditory stimuli as conditioned stimuli and a 100-ms airpuff as an unconditioned stimulus. The reinforced conditioned stimulus overlapped and co-terminated with the unconditioned stimulus whereas the non-reinforced conditioned stimulus was always presented alone. Consistent with previous results, hippocampal theta-band responses to the conditioned stimuli diminished in amplitude across training. Interestingly, hippocampal theta-band responses were most consistently time-locked when a well-trained animal failed to suppress behavioral learned responses to the non-reinforced conditioned stimulus. We suggest that phase-locking of hippocampal theta-band oscillations in response to external stimuli reflects retrieval of the dominant memory trace (adaptive or not) along with initiating the most prominent action scheme related to that memory trace.
authors.affiliation: Department of Psychology, P.O. Box 35, FI-40014 University of Jyväskylä, Finland.
authors.forename: Miriam S
authors.initials: MS
authors.lastname: Nokia
authors.forename: Jan
authors.initials: J
authors.lastname: Wikgren
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D003215:Conditioning, Eyelid / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D011817:Rabbits; D013826:Theta Rhythm / Q000502:physiology*
keywords: Conditioned response; Discrimination learning; Hippocampus; Phase locking; Theta