Robert M. Stutz

Memory loss following posttrial electrical stimulation of the hippocampus

Retention of a one-trial passive-avoidance response in rats was found to be disrupted by subconvulsive electrical stimulation of the hippocampus, which was administered immediately I following footshock. Lesions of the hippocampus or stimulation of anatomically related areas did not impair performance of the avoidance response significantly.

Stimulus Properties of Reinforcing Brain Shock

Rats easily discriminate between two types of subcortical brain shock which differ in reinforcing properties. When both stimuli are either neutral or positively reinforcing subjects have difficulty in responding differentially to the two types of electrical stimulation of the brain. Possible implications for a theory concerning a generalized or diffuse reinforcement system are discussed.

Intermodal transfer in temporal discrimination

This study determined if training for accuracy in temporal discrimination would transfer across sensory modalities. A fractionation method was used in which subjects bisected the durations of acoustic and visual signals at three standard intervals (6, 12, and 18 see). Absolute error was the performance index. Half of the subjects were trained with acoustic stimuli and then tested in vision; the remainder were trained in vision and tested in audition. Similar negatively accelerated acquisition functions were noted for both modalities. Positive intermodal transfer, characterized by symmetry across modalities, was obtained at all standard durations. The results were considered to provide support for the notion that a common mechanism underlies temporal discriminations in different sensory systems.

Discriminability of intracranial stimuli: The role of anatomical connectedness.

Abstract We have previously demonstrated a high degree of perceptual similarity between rewarding hypothalamic and septal brain shock. The present experiment attempted to evaluate the contribution of anatomical factors in determining the degree of stimulus equivalence. Eight rats were each implanted with positively reinforcing electrodes in the septum and the hypothalamus. They were then tested for their ability to solve a thirst-motivated water-reinforced successive discrimination task with stimulation of the two structures serving as the discriminative stimuli. Four animals had both electrodes placed on the same side of the brain (Ipsilateral Group), while in another four rats the electrodes were aimed at structures on opposite sides of the brain (Contralateral Group). The contralateral group reached the discrimination criterion significantly faster than the ipsilateral group. (i.e., the distributions were nonoverlapping.) The difficulty of making a discrimination between the stimulus properties of two types of rewarding brain shock seems to be directly related to the intimacy of the connections between the anatomical structures being stimulated.

Competition between food and rewarding brain shock

Abstract Some rats implanted with electrodes in the medial forebrain bundle or ventral tegmental nucleus prefer brain shock to food, even to the point of self-starvation. Non-contingent shock, however, does not seriously interfere with food intake or weight regulation. This suggests that positively reinforcing brain shock does not short-circuit a hunger regulatory mechanism.

Morphine and self-stimulation: Evidence for action on a common neural substrate

Recent studies have demonstrated that the self-stimulation phenomenon may provide a useful technique for investigating the rewarding properties of potentially addictive drugs such as morphine. The present study attempted to examine the nature of morphines effects on self-stimulation by observing changes in rate-intensity functions following morphine administration. The results indicate that morphine markedly enhanced bar pressing for low intensity stimulation when the intensities were presented in an ascending sequence but morphine produced only slight changes in self-stimulation rates when a descending series was used. The failure of morphine to facilitate responding in the descending series suggests that adaptation of the self-stimulation system can block morphines effects on this system. These findings appear to support the hypothesis that morphine affects the excitability of the neural system which mediates self-stimulation.

Flooding treatment of phobias: Does chronic diazepam increase effectiveness?

Abstract Flooding was combined with either chronic diazepam (15 mg/day) or placebo in the treatment of small animal phobias. Diazepam had no effect on the length of time required for successful treatment. This result is consistent with animal studies showing that tranquilizers do not enhance the effects of response prevention as a method of eliminating conditioned fears, but this result contrasts with human studies showing that flooding effects are enhanced if treatment sessions follow single doses of tranquilizers. It is suggested that differences in experimental outcome are attributable to whether flooding sessions overlap the waxing and waning of the drugged state.

The effect of alpha- and beta-adrenergic antagonists of the self-stimulation phenomenon

Abstract In an attempt to evaluate the possible existence of alpha- and/or beta- adrenergic components of the self-stimulation reward system, rats were injected (i.p.) with chlorpromazine hydrochloride (2.5 mg/kg), phentolamine hydrochloride (5 mg/kg), and propranolol hydrochloride (10 mg/kg). The alpha- adrenergic antagonists (chlorpromazine and pehntolamine) inhibited self-stimulation but the beta-adrenergic blocker (propranolol) was without significant effect. Self-stimulation is apparently mediated by the alpha-adrenergic system.

Cerebral Blood Flow Velocity and Task Engagement as Predictors of Vigilance Performance

Responses to a brief six-min screening battery involving high-workload tracking, verbal working memory, and line discrimination tasks were used to predict subsequent performance on a 36-min vigilance task. Two predictors of interest were subjective state, as indexed by the Dundee Stress State Questionnaire (DSSQ), and cerebral blood flow velocity (CBFV), measured via transcranial Doppler sonography. The results testify to the importance of assessing task-induced responses for predicting vigilance performance. They also indicate that forecasting vigilance performance is a complex endeavor requiring a set of multidimensional predictors. Specifically, higher post-battery task engagement scores on the DSSQ in this study and higher levels of CBFV in the left hemisphere during performance of the screening battery predicted more correct detections on the subsequent vigilance task. These findings are interpreted in the light of the resource-workload model of vigilance, and their practical significance is discussed.

Lateral hypothalamic stimulation: Stimulus-bound eating and self-deprivation ☆

Research was undertaken in an attempt to clarify the relationship between stimulus-bound eating and self-deprivation produced by electrical stimulation of the lateral hypothalamus. It was hypothesized that if these two phenomena are mediated through a common population of feeding-related neurons, a significant correlation should be observed between these two behaviors. No significant relationship was discovered among the rats tested for both stimulus-bound eating and self-deprivation. Although this finding by itself does not rule out some role for feeding-related neural elements in stimulus-bound eating and self-deprivation, the present results provide no support for this view and suggest alternative explanations should be sought.