Factors modulating the effects of teleost telencephalon ablation on retention, relearning, and extinction of instrumental avoidance behavior

Two experiments on the nature of avoidance behavior in the goldfish are reported. In the first experiment, a master/yoked design was used to determine the degree to which Pavlovian conditioning would generate acquisition of a shuttle response by goldfish. Results indicated that the mere sequence of signal-shock pairings experienced by the avoidance animals is not in this situation sufficient to explain the development of the instrumental avoidance responding. The second experiment was conducted to study the effects of three variables on the retention and extinction of the avoidance response. First, unilateral lesions of the telencephalon produced a transient deficit from which the subjects recovered to normal levels. Retention of the avoidance response after bilateral telencephalon ablation was impaired and never fully recovered with additional training. Second, this deficit was reduced under higher intensities of electric shock. Third, overtraining on the task before the ablation had only a nonsignificant enhancing effect on retention levels. Extinction was always poorer following ablation, independent of the type of ablation, intensity of shock, degree of overtraining, and terminal retention level of performance. The results are discussed in terms of various theories of telencephalic function in fish.     

Hypothalamo-pituitary-adrenal manipulations and stress ulcerations in rats

Both gastric ulceration and activation of the hypothalamo-pituitary adrenal axis are considered integral to the stress response, and a causal relationship between the two has been suggested. In the present study, corticosterone secretion in rats was either stimulated with CRF or lowered with metyrapone during a known ulcerogenic stress. Reduction of circulating corticosterone during the stress had no effect on ulceration severity compared to saline-treated stressed control rats. Treatment with CRF in stressed animals reduced ulceration severity. The mechanism of this protective effect remains unclear. The findings do not support a simple causal relationship between adrenocortical activity and gastric ulceration.     

Teleost telencephalon and learning: An interpretive review of data and hypotheses

Normal and telencephalon ablated teleost fish were compared with respect to learning under classical conditioning, instrumental training, and avoidance paradigms. Telencephalic ablation appears not to affect classical conditioning and learning of simple instrumental behaviors (escape and food-getting). However, performances on some complex instrumental tasks and all avoidance tasks are impaired by such ablation. Analysis of the various tasks attempted to isolate those factors which lead to the selective poorer learning by ablated fish. Increased opportunity for response variability and delay of primary reinforcement were implicated. Several hypotheses about teleost telencephalic function were considered: (a) non-specific arousal, (b) dominant response inhibition, (c) short-term memory, and (d) integration of separate learning processes. Support for and shortcomings of each hypothesis were reviewed. A new hypothesis was proposed; it is that the teleost telencephalon mediates utilization of changes in conditioned motivational states that permit reinforcement of behavior. Appropriate tests were suggested. Teleost telencephalic ablation was related to current physiological issues and learning theory questions.     

Trauma and resulting sensitization effects are modulated by psychological factors

Traumas have both immediate consequences and proactive consequences. Examples include learned helplessness, HPA-axis responsivity, gastrointestinal vulnerability to ulcer, and other correlates of anxiety disorders. Both immediate and proactive consequences may be modulated by behavioral and cognitive evolutionary evolved adaption processes, among which are forms of learning that enable ‘coping’. Examples of associative and non-associative forms of coping and effects on learned helplessness, HPA-axis responsivity, and gastrointestinal vulnerability are presented. The importance of attention to behavioral contingencies in situations in which potentially traumatic events occur is emphasized as critical to understanding that it is not the physical event(s) per se that determine the immediate and long term consequences.     

Hemispheric Asymmetry and Human Classical Conditioning to Verbal and Non-Verbal Visual CSs

A new paradigm called “the dichoplic acquisition paradigm” was developed to study Ihc effects of hemispheric asymmetry on classical etcctrodcrmal conditioning. The paradigm involves three phases: 1) A habituation phase where two different color-words written in two incongruent colors are tachistoscopically displayed bilaterally to the visual half-fields left and right of center fixation; 2) An acquisition phase, wherein the display is followed by a 105dB white noise on each trial; and 3) An extinction phase, where each of the four CS cues (two color-words and two colors) are separately presented bilaterally for simultaneous input to both hemispheres. Here the color-words are now presented in grey against a black background, and the colors as color-bars against the same background. A control group had no UCS presentations. Bilateral skin conductance responses (SCRs) of right-handed males were used to evaluate conditioning. Conditioning to the CS color-word previously presented in the right half-field (i.e. initial left-hemisphere input) during acquisition led to larger SCRs during extinction, than the color-word previously presented in the left half-held (i.e. initial right-hemisphere input). In contrast, the CS color cue previously presented in the left half-field during acquisition resulted in larger SCRs during the first extinction trial, than the CS color cue previously presented in the right half-field. Thus, the present experiment revealed effects of hemispheric asymmetry on human electrodermal conditioning.     

Differential outcomes effect in children and adults with down syndrome

In previous studies, researchers have demonstrated that learning of symbolic relations is facilitated when a particular outcome is associated with each relation to be learned. In the present study, we extend this differential outcomes procedure to children and adults with Down syndrome who had to learn a symbolic conditional discrimination task. Participants showed a better terminal accuracy and a faster learning of the task when the alternative correct responses were each followed by unique different outcomes than when nondifferential outcomes were arranged. These findings confirm that the differential outcomes procedure can be a useful tool to ameliorate discriminative learning deficits and demonstrate the benefits of this procedure for people with Down syndrome.     

Effects of telencephalic ablation on trace classical conditioning of heart rate in goldfish

As a test of the hypothesis that telencephalic (forebrain) ablation impairs short-term-memory functions in fish, normal and forebrain-ablated goldfish were compared on trace classical conditioning of heart rate using aversive conditioning procedures. Because the signal and shock do not overlap in this procedure, short-term-memory is required if conditioning is to proceed. The normal and forebrainless groups did not differ in rate of acquisition or asymptotic level of conditioning, using percentage decrease in heart rate as the index. These results indicate that the simple short-term-memory hypothesis of teleost forebrain function is probably incorrect and that fore-brain-ablation-produced deficits are specific to tasks involving behavior instrumental in gaining goals.     

Poststress effects of danger and safety signals on gastric ulceration in rats

Gastric ulceration of rats stressed by restraint in 19 degrees C water for 75 min was markedly increased by allowing a 75-min postrestraint room-temperature rest period during which the rat was exposed to cues that had previously been associated with the delivery of 80 5-s uncontrollable electric shocks distributed over four sessions. This effect obtained equally without regard to whether the "danger cues" were punctate signals or constant contextual cues or whether contextual ones were interrupted by punctate safety signals. The experimental treatments used were unusual in that they equated the groups on their total conditioning history and thus allowed a more pure look at the poststress effect than heretofore. Other groups provided controls for prior shocks, rest, and their interaction as well as handling. Analyses of corticosterone after the stress or stress-rest cycle revealed only a general decline in corticosterone levels with rest undifferentiated across groups.     

Quality of poststressor rest influences the ulcerative process

Gastric ulceration in rats is exacerbated by allowing a so-called recovery period after exposure to an ulcerogenic stressor. One hypothesis, which has support from pharmacological studies, argues that this effect is brought about by a rebound of parasympathetic activation. We tested this parasympathetic rebound hypothesis by presenting animals with a fear-inducing (sympathetic-activating) conditioned stimulus (CS) after 2 hr of water-restraint stress. Contrary to the hypothesis, presentation of such a CS increased severity of ulceration compared with those animals that did not receive the CS after restraint stress and control animals. These ulceration data favor instead a sustained activation hypothesis for ulceration, whereby presentation of the CS effectively prolonged the length of time during which animals were under stress, thus enhancing the degree of ulceration. Measurement of plasma corticosterone however indicated a negative correlation between adrenocortical activity and degree of gastric ulceration, contrary to that expected by a sustained activation hypothesis. It is suggested that this inconsistency may be because of the activating of a pituitary-endorphinogenic mediated stress analgesia.