Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Abstract

Conditioned suppression of photokinesis by the marine mollusc Hermissenda was examined in 3 experiments. In each experiment, groups of animals received light (the conditioned stimulus, CS) that was paired with high-speed orbital rotation (the unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. Twenty-four hours after training, all animals were tested for suppression of photokinesis in the presence of the light. To establish the effectiveness of our conditioning procedure, in Experiment 1 individual groups of animals received either 50, 100, or 150 CS-UCS pairings. Fifty pairings resulted in a marginal suppression of photokinesis, whereas 100 and 150 pairings produced strong suppression. In Experiment 2, the delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. As predicted by the current understanding of Hermissenda's neural network, in Experiment 3 it was found that CS-UCS pairings in which the CS preceded the onset of the UCS and terminated with the offset of the UCS evoked stronger conditioned suppression than either a CS that preceded the UCS and terminated with its onset or a CS that was paired in simultaneous compound with the UCS. This result indicates that CS-UCS contiguity as well as the forward ISI act additively to establish the CS-UCS association. In none of the 3 experiments were any differences observed between groups that were untreated and that received the CS and UCS unpaired. In total, these experiments suggest strong similarities in the temporal characteristics of associative learning in Hermissenda and vertebrate species.

Chemosensory-based contextual conditioning inHermissenda crassicornis

“…used longduration (30 sec) turntable-induced rotation to achieve vestibular stimulation. In contrast, we have successfully used brief (2-3 sec) orbital rotation as a US in numerous studies (Matzel & Rogers, 1993;Matzel, Schreurs, Lederhendler, & Alkon, 1990;Rogers, Fass, & Matzel, 1992;Rogers et a\., 1994). Although both techniques result in the stimulation ofhair cells within the vestibular organ, differences arise as to the pattern of stimulation.…”

Imaging learning and memory: Classical conditioning

“…Simultaneous measurement of both locomotion and foot contraction revealed that there is a rapid decrease in locomotion and a gradual increase in foot contraction as a function of training (Matzel et al, 1990a). Finally, foot contraction was also shown to be a function of the number of CS-US pairings and of the interval between the CS and US (Matzel et al, 1990b).…”

A Model Of Associative Learning In Hermissenda Crassicornis: Sensitin'ities To Temporal Relationships Of Stimuli

“…This expectation has been verified in animal experiments using 30 second [SI and shorter [6] stimuli. The model also exhibits effective learning only when the CS and the US coterminate.…”

“…For effective learning to occur, the time interval between the onsets of the light and rotation must occur within a narrow range. A behavioral experiment that examined the role of the IS1 in associative learning was performed by Matzel et al [6]. In this experiment, the animals were presented with 150 repetitions of light (CS) paired with rotation (US).…”