Hippocampal theta-band activity and trace eyeblink conditioning in rabbits.

Abstract

We aimed to examine the relationship between hippocampal theta activity and trace eyeblink conditioning. Hippocampal electrophysiological local field potentials were recorded before, during, and after conditioning or explicitly unpaired training sessions in adult male New Zealand White rabbits. As expected, a high relative power of theta activity (theta ratio) in the hippocampus predicted faster acquisition of the conditioned response during trace conditioning, but, contrary to previous results obtained using the delay paradigm, only in the initial stage of learning. The presentation of the conditioned stimulus overall elicited an increase in the hippocampal theta ratio. The theta ratio decreased in the unpaired group as a function of training, remained high throughout conditioning in the fast learners and rapidly increased in the slow learners initially showing a low theta ratio. Our results indicate a reciprocal connection between the hippocampal oscillatory activity and associative learning.The hippocampal theta ratio seems to reflect changes and differences in the subjects' alertness and responsiveness to external stimuli, which affect the rate of learning, and are in turn affected by both conditioning and unpaired training.

Phase matters: responding to and learning about peripheral stimuli depends on hippocampal θ phase at stimulus onset

“…High-amplitude, well phase-locked hippocampal fissure u-band responses to the conditioned stimulus early in training predicted better learning of trace eyeblink conditioning Previous studies indicate a correlation between hippocampal function and learning only, or at least especially, early in training (Nokia et al 2009). To study the link between hippocampal uband responses and learning, we calculated correlations between the relative amplitude/phase-locking of hippocampal u-band responses to the CS during the first conditioning session and the percentage of CRs elicited during conditioning (blocks 1 -8).…”

“…Previous studies indicate that the spontaneous level of hippocampal u activity predicts subsequent learning (Berry and Thompson 1978;Nokia et al 2009). Thus, to ensure there was no underlying difference in baseline u between the Peak and the Trough groups, data from a 5-min stimulus-free recording conducted immediately before the first conditioning session were analyzed.…”

“…Relative magnitude of hippocampal u-band (4-8 Hz) oscillations: u ratio u ratio (Nokia et al 2009) was obtained from a 5-min baseline recording conducted immediately prior to the first conditioning session. To this end, the hippocampal fissure signal was analyzed in 1500-msec sweeps using the FFT.…”

“…u is thought to reflect a state in which information about the surroundings is actively acquired (Buzsáki 1989). Animals exhibiting dominant hippocampal u during spontaneous recordings prior to training tend to learn better (Berry and Thompson 1978;Nokia et al 2009Nokia et al , 2012b, and high-amplitude, well phase-locked u-band hippocampal responses to the conditioned stimulus early in eyeblink conditioning predict good learning (Nokia et al 2009(Nokia et al , 2010(Nokia et al , 2012aNokia and Wikgren 2014). Training contingent on transient episodes of hippocampal u or its explicit absence has produced significant but somewhat inconsistent effects on learning (Griffin et al 2004;Nokia and Wikgren 2014).…”

Hippocampal Ripple-Contingent Training Accelerates Trace Eyeblink Conditioning and Retards Extinction in Rabbits

“…Previously, CS-evoked theta-band phase locking (Siegel et al, 2009) and theta oscillation in general (Nokia et al, 2009) have been shown to strengthen immediately preceding the onset of CR acquisition in the course of trace eyeblink conditioning. At the neuronal level, phase locking of neural oscillations within a structure, as well as synchronized oscillations between functionally related brain structures, allows predictability in terms of neuronal communication.…”