Contradictory evidence for aversion to auditory stimuli resulting from different test methods

Avoidance Learning as a Function of CS Quality and CS Termination on Escape Trials

Rats were trained in a shuttle box with 1 of 5 CSs and with either immediate or delayed CS termination on escape trials. An avoidance response always produced immediate CS termination. Differences among CSs were found, but with all CSs there was a decrement under the delay condition. This decrement is explained on the basis that CS termination serves as a reinforcing safety signal, and the safety signal is more effective when it is response contingent.

Free-operant escape-avoidance of noise by rats

A series of experiments was conducted to establish free-operant escape-avoidance responding in rats using noise as the stimulus. Naive rats did not acquire a bar-press response on an escape-avoidance of noise schedule. Similarly, free-operant responding established using escape-avoidance of shock was not maintained when noise was substituted for shock. Noise stimuli of 110 dB did maintain responding, but at a lower level than during training, when the noise stimuli had first been paired with shock. Noise stimuli of 97 dB and 87 dB were not effective under those same conditions. Additional rats were trained on a free-operant escape-avoidance schedule of shock and then exposed to a delayed conditioning procedure in which noise was the conditioned stimulus and shock was the unconditioned stimulus. When these subjects were then tested with noise alone, two of the three subjects conditioned and tested with 105-dB noise displayed escape-avoidance of noise, but none of the rats conditioned and tested at 97 dB displayed escape-avoidance of noise. The results suggest that free-operant escape-avoidance of noise can be demonstrated; however, only higher intensity noise stimuli that have been paired with shock are effective.

Latent inhibition is attenuated by noise and partially restored by a 5-HT2A receptor antagonist

Latent inhibition (LI) is a model of attention, which is a cognitive process that can be modulated by stressors such as chronic intermittent broadband noise, e.g. caused by building work, which is particularly stressful to rats. The aim of this study was to analyse the effect of chronic noise stress, caused by a building project, on LI, and its interaction with SR 46,349B, a 5-HT2A receptor antagonist. Control groups from LI experiments conducted during periods of chronic intermittent noise were compared with control groups from LI experiments conducted in normal quiet conditions. The interaction of SR 46,349B with the effects of chronic noise stress was then tested. Chronic intermittent noise attenuated LI, an effect which was partially reversed by SR 46,349B, 2.4 mg/kg i.p. Attenuation of LI by chronic intermittent noise and reversal of this effect by SR 46,349B support suggestions that stress can modulate attention and that 5-HT2A receptors are involved in mediating the effects of chronic stress.

Associative learning and latent inhibition in a conditioned suppression paradigm in humans

A paradigm based on conditioned suppression of ongoing motor activity, sensitive to latent inhibition (LI), was developed and tested in healthy volunteers. Subjects were trained to move disks from one peg to another with a high degree of regularity in the Tower of Toronto puzzle, a well-known cognitive skill learning task. Once this was achieved, they were submitted to a Pavlovian conditioning procedure. The conditioned stimulus (CS) was a pure tone and the unconditioned stimulus (US) a loud white noise. The resulting response suppression was assessed by a transient increase in latency of the hand movements. In control subjects, there was non-contingent CS and US presentation. The results evidenced conditioning after a single CS-US pairing. Following five preexposures to the to-be-conditioned CS, however, conditioning was abolished, seemingly expressing LI. Because a weak unconditioned response to the tone was observed after its first two presentations, an additional experiment was performed with two preexposures to the to-be-conditioned CS. With such procedure, conditioning was obtained, supporting the existence of LI in the preceding experiment. These results indicate that the present paradigm may be useful for the study of LI in human subjects, having the advantage of being similar to the experimental conditions used in the majority of LI studies in experimental animals.