Physiological Psychology

Two studies were conducted to study the effects of unpaired sucrose (CS) experiences on the acquisition, retention, and reacquisition of a sucrose aversion. In Experiment 1, rats received 0, 1, or 3 preconditioning CS exposures and/or 0, 1, or 3 postconditioning CS exposures. Sucrose exposures prior to conditioning interfered with the acquisition of a sucrose aversion, while sucrose-only experience following a single taste-illness pairing retroactively interfered with retention of the sucrose aversion and proactively interfered with the reacquisition of the sucrose aversion. In Experiment 2, two unpaired sucrose experiences following each sucrose-illness pairing (33% PRF group) resulted in little apparent sucrose aversion after six sucrose-illness pairings, while a single unpaired sucrose experience after each conditioning trial (50% PRF group) produced a moderate level of interference compared to the rapid acquisition in rats receiving only sucrose-illness pairings (CRF group). It is suggested that CS familiarization and extinction may represent a single process where the rat learns that a taste cue predicts no illness, and that this expectancy can interfere with the development of an aversion or impair the ability of the animal to reacquire a previously acquired taste aversion.

Male Sprague-Dawley rats received either successive discrimination training or continuous reward in a straight alley with a 24-h intertriai interval. Plasma corticosterone levels were determined after moderate (18 trials) and extended (46 trials) acquisition in Experiment I and after 20 trials in Experiment II. Increases in plasma corticosterone levels following nonreward in the discrimination groups or in subjects previously given 45 continuous reward trials were not significant relative to two control groups. These results fail to support the proposal that the pituitary-adrenal system is sensitive to downward reinforcement shifts (frustration effects) under widely spaced trials.

Measures of reaction time and cardiac activity were recorded from 10 males and 10 female subjects during a variable foreperiod reaction time task. Males showed faster reaction times, greater cardiac decelerations, and higher levels of heart-rate variability during the foreperiod. Trend analyses revealed sex differences in the heart-rate response to the onset of the warning signal, but not in the response to the imperative signal. These results indicate that those measures of cardiac activity which have been shown previously to predict performance tend to differentiate between the sexes when there are sex differences in performance.

Taste aversion to a.1% saccharin (sacc) solution was induced in rats by pairing sacc consumption with an oral dose of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). In Experiment 1, a critical dose range for producing taste aversion with 2,4,5-T was found from between 15 and 40 mg/kg and upwards. In Experiment 2, preconditioning exposure of the animals to sacc and/or the 2,4,5-T injection reduced the strength of the aversion. The possible risk of producing alterations of food preferences in wildlife through a widespread use of 2,4,5-T as a herbicide is discussed.

Twenty-four hours after the administration of a footshock (FS) followed 4 or 256 sec later by an electroconvulsive shock (ECS), rats exhibited amnesia for the aversive experience. They were then given a “reminder” cue (tone), which was earlier paired as a conditioned stimulus with footshocks. Presentation of the tone resulted in attenuation of the amnestic effect in FS-ECS 256-sec delay group but failed to alter the amnestic effect in FS-ECS 4-sec delay group. Results were interpreted in support of an “incomplete” memory consolidation hypothesis.

Blindfolded cats in which SII and adjacent areas had been ablated were tested for their ability to locate cutaneous stimuli as demonstrated by their bringing the mouth into contact with the stimulated point. During recovery, seven cats went through a phase in which they displayed dissociations of the vertical and horizontal components of the orientation-localization movement: either they moved the head downward before initiating any lateral movement or they turned towards the side of stimulation well before achieving accurate proximodistal localization. Hypotheses are offered about which aspects of anatomy and physiology are involved in proximodistal and lateral localization, and a simple mathematical model is given to suggest that one reason why such central associative functions in movement may have evolved is because they require fewer neurons than an alternative conceivable design.