Biomedical subjects

Antonio Cándido

Publications and source records attributed to Antonio Cándido.

4 recordsLinked to original sources

PubMed2004

Safety signals from avoidance learning but not from yoked classical conditioning training pass both summation and retardation tests for inhibition.

In one experiment half of the animals were trained to avoid a signaled footshock by jumping (30 or 160 trials), whereas the rest of the animals received the same events as yoked. For all of them the termination of the warning signal and of the shock was followed by a safety signal. Several tests were conducted to assess the ability of the stimuli to suppress licking by measuring the latency in completing 25 consecutive licks in the presence of the stimuli. Fear of the warning signal and inhibitory properties of the safety signal (summation and retardation tests) were measured. The results showed that there were no differences in fear to the warning signal, and that the safety signal behaves as a conditioned inhibitor only for animals trained with a long avoidance procedure, but not in the yoked (classical conditioning) procedure. These results highlight the role played by the avoidance response and its consequences in avoidance learning.

Animals↗

PubMed2003

Repeated administration of LiCl produces an unconditioned stimulus preexposure effect in backward excitatory CTA but not habituation of the unconditioned increment in neophobia.

In one experiment using conditioned taste aversion and the unconditioned stimulus (US) preexposure procedure, one group of rats was given LiCl exposure for 3 days, whereas two other groups received saline. Following this phase, all groups were given a novel flavour (saccharine) to drink following either LiCl (group preexposed and one of the control groups) or saline injections (the remaining control group) and the consumption of the flavour was assessed. After this neophobia test, the acquired saccharine aversion was evaluated. The results show that three LiCl injections are enough to produce a US preexposure effect on backward excitatory taste aversion conditioning, whereas this number of injections procedure does not produce habituation of the increment in neophobia, an unconditioned response to the LiCl. The results are discussed taking into account different mechanisms involved in US preexposure effect.

Journal Article↗

PubMed2003

The role of injection cues in the associative control of the US pre-exposure effect in flavour aversion learning.

Two experiments, using rats as subjects, examined the role of contextual cues in producing the unconditioned stimulus (US) pre-exposure effect in conditioned taste aversion. Experiment 1 showed a significant US pre-exposure effect, when the pre-exposure was conducted in a familiar context, and that a change of context between the pre-exposure and conditioning phases did not attenuate this effect. Experiment 2 demonstrated that extinction of injection-related cues after the pre-exposure stage attenuated the US pre-exposure effect, when the pre-exposure was conducted in either a familiar or a novel context. Taken together, these results support the associative explanation of the US pre-exposure effect in terms of blocking, incorporating a role for injection-related cues in the context blocking analysis of the US pre-exposure effect.

Animals↗

PubMed2002

Successive positive contrast in one-way avoidance learning.

The main finding of these experiments was a positive contrast effect in one-way avoidance learning. Experiment 1 showed that increasing safety time during one-way avoidance training led to improved performance, surpassing that of a control group that had received the high reward (safe time) from the beginning of training. Experiment 2 showed that a similar positive contrast effect occurred when the time spent in the danger compartment before the onset of the warning signal was shortened. These results suggest that time spent in a safe context acts as a reinforcer of the avoidance response; however, its incentive value depends not only on its duration, but also on the length of the time spent in the danger compartment before the onset of the signal. Overall, results also suggest that the avoidance response is a mixture of flight (motivated by fear) and approach (to a safe place) behaviour. The specific weight of the flight or approach component may be a function of the time and the amount of activation of each emotional state (fear or relief) due to opponent homeostatic compensatory processes that occur in the danger and safe compartments during one-way avoidance learning.

Animals↗