1. US location switch alone
Cross-Modal Savings in the Contralateral Eyelid During Eyeblink Conditioning in Rats
Eric W. Buss, Matthew M. Campolattaro & John H. Freeman
Department of Psychology, University of Iowa
Introduction
Unconditioned Responses
US location switch alone
Cross-modal savings occurs when a CS-US association is first acquired using one modality CS (e.g., a tone) and subsequent learning with a different modality CS (e.g., a light) is greatly enhanced (Campolattaro & Freeman, 2009; Kehoe, 1988). Evidence of cross-modal savings of eyeblink conditioning primarily comes from studies that have recorded from the same eye during initial acquisition and subsequent testing with the new modality CS. However, a previous study found that rabbits only show modest savings of eyeblink conditioning when both location of the unconditioned stimulus (US) and CS modality (i.e., from a clicker to light CS) are changed before the cross-modal transfer test (Pearce, Montgomery, & Dickinson, 1981). An open question is whether rats show the same rate of cross-modal transfer under similar training conditions. The present study was designed to continuously monitor bilateral eyelid activity during eyeblink conditioning in rats using unilateral US presentations. This type of training is effective for producing bilateral conditioned eyeblink responses in rats (Campolattaro & Freeman, in press) and sometimes in rabbits (Lee, Kim, & Wagner, 2008; 2009). Three groups of rats were initially given paired or unpaired conditioning with a CS and US. All rats then received additional training but the US location (group 1), CS modality (group 2) or both US location and CS modality (group 3) were changed.
Group 1
Amplitude
Unpaired →Paired
Paired →Paired
CR% by block
Summary & Conclusions
All rats given paired CS-US trials acquired high levels of CRs in both eyelids during initial training, but acquisition was faster, CR percentage was higher, and CR amplitude was larger in the eyelid that was ipsilateral to the US.
All rats given unpaired CS/US trials did not acquire CRs in either eyelid during initial training.
Changing the location of the US alone after initial conditioning resulted in almost immediate transfer of conditioning in both eyelids for paired-paired rats in Group 1.
Facilitated learning to the new modality CS was observed in Groups 2 & 3 paired-paired rats, indicating that cross-modal savings occurs robustly whether or not the location of the US is switched.
Conditioning consistently becomes dominated by the reinforced eyelid in measures of CR percentage and CR amplitude.
Methods
Subjects: 48 adult male Long Evans rats.
Surgery: The rats were fitted with differential electromyograph (EMG) electrodes that were implanted in the upper left and right eyelid muscles (orbicularis oculi). Bipolar stimulating electrodes (for delivering the shock US) were implanted subdermally, immediately caudal to each eye.
Conditioning Procedures: Each group first received ten daily 100-trial sessions of paired or unpaired eyeblink conditioning with a 400 msec CS (2 kHz, 85d tone or 6 W light; counterbalanced tone vs light) and a unilateral 25 msec periorbital shock US (1-2 mA; counterbalanced left vs right). The groups were then given five daily sessions of paired training but the US location (group 1), CS modality (group 2) or both US location and CS modality (group 3) were changed.
Responses: CRs were defined as EMG activity that exceeded a threshold of 0.4 units (amplified and integrated units in volts) above the baseline mean during the CS period after 80 ms. CRs during CS-US trials were defined as responses obtained after the baseline period, but before the onset of the US.
CS modality switch alone
Group 2
Paired →Paired
Unpaired →Paired
Amplitude
CR% by block
Eyeblink Conditioning
US location and CS modality switch together
Group 3
References
Paired →Paired
Unpaired →Paired
Amplitude
CR% by block
Campolattaro, M. M. & Freeman, J. F. An examination of bilateral eyeblink conditioning in rats. Behavioral Neuroscience, in press.
Campolattaro, M. M. & Freeman, J. F. (2009). Cerebellar inactivation impairs cross modal savings of eyeblink conditioning. Behavioral Neuroscience, 123(2),
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Lee, T., Kim, J. J., & Wagner, A. R. (2008). Bilateral nature of the conditioned eyeblink response in the rabbit: Behavioral characteristics and potential mechanisms. Behavioral Neuroscience, 122(6),
Lee, T., Kim, J. J., & Wagner, A. R. (2009). Discriminative Conditioning with different CS-US intervals produces temporally differentiated conditioned responses in the two eyes of the rabbit (Oryctolagus cuniculus). Behavioral Neuroscience, 123(5),
Pearce, J. M., Montgomery, A., & Dickinson, A. (1981). Contralateral transfer of inhibitory and excitatory eyelid conditioning in the rabbit. Quarterly Journal of Experimental Psychology Section B-Comparative and Physiological Psychology, 33,
Bilateral Eyelid EMG Responses
Campolattaro & Freeman, in press