Examination of bilateral eyeblink conditioning in rats

Abstract

This experiment monitored eyelid responses bilaterally during delay eyeblink conditioning in rats. Rats were given paired or unpaired training with a tone or light conditioned stimulus (CS) and a unilateral periorbital shock unconditioned stimulus (US). Rats given paired training acquired high levels of conditioned responses (CRs), which occurred in both eyelids. However, acquisition was faster, and the overall percentage of CRs was greater in the eyelid that was ipsilateral to the US. CRs in the eyelid ipsilateral to the US also had shorter onset latencies and larger amplitudes than CRs in the contralateral eyelid. Both eyelids consistently showed high percentages of unconditioned responses (UR) to the US, and the UR amplitude decreased across training sessions in the paired group. The present study demonstrated that CRs occur robustly in both eyelids of rats given eyeblink conditioning, which is similar to previous findings in humans and monkeys. The results also showed that conditioning occurs more prominently in the eyelid that is ipsilateral to the US, which is similar to previous findings in humans, monkeys, dogs, and rabbits.

Figure 1

Mean (± SEM) conditioned response (CR) percentage (A), amplitude (B), onset latency (C) and peak latency (D) recorded in the eyelids that were ipsilateral (black plots) and contralateral (white plots) to the location of the unconditioned stimulus (US). Rats were given either paired (P; circles) or unpaired (UP; triangles) training with a tone or light CS and the US. The timescale for the CR onset and peak latency data is relative to the onset of the conditioned stimulus. The horizontal dashed line shows the onset of the US.

Figure 2

Composite EMG activity for the eyelids that were ipsilateral (solid line) and contralateral (dashed line) to the location of the unconditioned stimulus (US) during sessions 1, 5 and 10. Eyelid responses were elicited by the conditioned stimulus (CS) on CS-alone probe trials (A) and to the US on paired trials (B) for rats given paired training. Eyelid responses were elicited to US-alone presentations (C) for rats given unpaired training.