Retention and acquisition of classical trace conditioned responses by rabbits with hippocampal lesions.

Abstract

The effects of dorsal hippocampal lesions on retention of classical trace conditioned responses were examined using the rabbit nictitating membrane preparation. Animals were trained to criteria and then lesioned either in the cortex or in the hippocampus and the cortex. Hippocampal damage had no effect on the retention of responses but produced significantly longer onset latencies. A control group of hippocampal animals acquired conditioned responses (CRs) at least as quickly as the prelesion subjects, and they also exhibited longer response onset latency. A second experiment evaluated the performance of hippocampal lesioned animals in classical trace conditioning with either a low-intensity periorbital shock or corneal air puff as the unconditioned stimulus (UCS). Hippocampal animals successfully acquired CRs under both conditions but exhibited an alteration of response onset which was dependent on the form of the UCS. Hippocampal animals displayed shorter response onset in the air-puff condition and longer response onset in the shock condition. Cortical animals timed responses consistently regardless of the UCS. These findings strongly suggest that the hippocampus modulates temporal characteristics of learned behavior.

Neural systems implicated in delayed and probabilistic reinforcement

“…the lesioned subject experiences the delay to the large reinforcer as longer than it actually is, causing it to value the reinforcer less than shams). The evidence for the role of the H in temporal perception is inconclusive: some studies have found that aspirative hippocampal lesions did not affect timing behaviour (Dietrich & Allen, 1998;Dietrich, Allen, & Bunnell, 1997;Port, Romano, Steinmetz, Mikhail, & Patterson, 1986;Rawlins, Winocur, & Gray, 1983), whereas others have suggested that lesions of the hippocampus or fimbria/fornix speed up an internal clock, or reduce the estimation of time periods when a stimulus being timed is interrupted (Hata & Okaichi, 1998;Meck, 1988;Meck, Church, & Olton, 1984;Olton, Meck, & Church, 1987;Wallenstein, Eichenbaum, & Hasselmo, 1998). In any case, H-lesioned rats were better at learning with delayed reinforcement but worse at choosing it, suggesting that self-controlled choice and learning with delayed reinforcement tax different psychological processes.…”

A neural model of timed response learning in the cerebellum

“…However, neurons in hippocampus display activation profiles that match the topography of the CR in the NMR conditioning task (Berger eta!., 1976;Berger & Thompson, 1978;Clark et al, 1984;Solomon eta!., 1986). In addition, hippocampal lesions can sometimes disrupt timing of the CR in trace conditioning (Port et al, 1986a;Solomon et al, 1986) and more complicated paradigms (Orr & Berger, 1985;Port eta!., 1986b). This experimental data has implicated the hippocampus in the timing of the NMR.…”

Effect of varying the intensity and train frequency of forelimb and cerebellar mossy fiber conditioned stimuli on the latency of conditioned eye-blink responses in decerebrate ferrets.

“…For instance, several investigators have suggested that the hippocampus performs a temporal processing that is utilized by the cerebellum (see e.g., Port et al 1986;Christiansen and Schmajuk 1992). It is therefore of interest to determine to what extent conditioning, which uses direct stimulation of the mossy fiber input to the cerebellum as the CS, resembles conditioning to a peripheral CS.…”