Assessment of the neural substrate for intracranial self-stimulation by the postreinforcement pause technique.

The poststimulation excitability of neurons mediating intracranial self-stimulation (ICSS) was evaluated by the paired-pulse method. Stimulus effectiveness was assessed by the postreinforcement pause (PRP) and by frequency threshold (FT) determinations in 7 rats performing ICSS in the medial forebrain bundle (MFB) and in the ventral tegmental area (VTA). Stimulus effectiveness values were minimal at conditioning-test (C-T) pulse intervals of 0.6 and 0.8 ms for MFB and VTA animals, respectively, because of neuronal refractoriness. Local potential summation could account for the increase in effectiveness at very short C-T intervals, and an additional peak of enhanced effectiveness at a C-T interval of 2.0 ms, perhaps reflecting synaptic events, was observed only in VTA animals with the PRP method. Important advantages of the PRP method were that the C-T interval was the only stimulus parameter that was varied, and the behavioral output of the animal remained relatively constant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A simple stimulator for electrical self-stimulation of the brain

A computer follow-up system has been developed which automatically prepares follow-up summaries for consultant physicians. This makes it possible to provide reliable feedback of diagnostic information in place of the traditional but haphazard word-of-mouth process. This system has been tested initially for surgical and autopsy-pathology follow-up of neuroradiology and nuclear medicine consultations using report conclusions available from the UCLA Natural Language Information Storage and Retrieval System.     

Temporal integration in self-stimulation: A paradox.

Investigated temporal summation of the rewarding effects of medial forebrain stimulation in 4 male Sprague-Dawley rats by varying the interval separating the 2 short bursts of stimulation given as a reward in a runway. One finding of Exp I—that the reinforcing effect of the 2 bursts was independent of interburst interval—supports a model in which there is perfect summation of the portion of the reward signal that exceeds some threshold. However, Exp II (with the Ss from Exp I) showed that charge–duration functions obtained with different levels of performance differed by a multiplicative (scalar) factor—that is, the ratio between the values of the 2 functions was everywhere the same. The models of postsynaptic integration are not capable of explaining simultaneously the fact (a) that the strength–duration function is a perfect hyperbola that has nearly reached its rheobase at a train duration no greater than 2 sec; (b) that there is no detectable effect of interburst interval on summation between bursts separated by intervals up to 2 sec and longer; and (c) that the strength–duration functions (or, equivalently, the charge–duration functions) derived by using different performance criteria differ by a multiplicative factor. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A systematic evaluation of the properties of self-stimulation train-duration response functions.

A series of experiments examined the characteristics of train-duration response functions and two statistics derived from these functions: train-duration thresholds and maximum rates. Train-duration response functions exhibited a steplike appearance. The slope of the train-duration curves was not influenced by either reward or performance manipulations, which suggests that the animals were not matching their response rates to changes in these factors along the steep part of the function. Substantial shifts in train-duration thresholds were observed following changes in the reward value of the brain stimulation, whereas maximum rates were affected by changes in factors such as response effort. The results of Experiments 1 through 6 demonstrate several similarities and differences between train-duration response functions and the reward summation functions generated with manipulations of stimulation frequency. The experiments described in this report provide convergent evidence for the validity of both of these approaches. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dorsal diencephalic self-stimulation: A movable electrode mapping study.

The function relating electrical self-stimulation (ESS) barpressing rate to the frequency of cathodal pulses (0.2 mA and 0.1 msec) was obtained for several positions of a movable electrode in the dorsal diencephalon of the rat. The rate–frequency functions were fitted to a sigmoid model to obtain the asymptotic rate and threshold frequency. ESS was found along the epithalamic route (stria medullaris, habenula, and fasciculus retroflexus) and in the following thalamic nuclei: mediodorsal, paratenial, interanteromedial, centromedial, reuniens, and rhomboid. The lowest threshold (～5 pulses/train), which was found in the stria medullaris and the junction of the paratenial and centromedial nuclei, was comparable to that usually obtained for the brain areas where the ESS is most effectively rewarding (medial forebrain bundle, dorsal raphe, and amygdala). However, most threshold estimates were 4 to 8 times higher. In most brain sites, ESS was accompanied by epileptiform, motor, or aversive reactions (or a combination of these). These reactions may explain the fact that the maximum rates were generally very low. Nevertheless, no correlation was found between maximum rates and threshold frequencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intracranial self-stimulation of the dorsal raphe sensitizes psychostimulant locomotion.

The authors hypothesized that repeated rewarding electrical stimulation of the dorsal raphe can produce behavioral sensitization to psychostimulants. Groups of male rats were implanted with a stimulation electrode and preexposed to brain stimulation at parameters set to equate rewarding effectiveness across rats. Control groups were implanted with an electrode but never stimulated, or not implanted at all. Twenty-four hours after the 12th self-stimulation session, all groups were challenged with amphetamine (0.5 mg/kg, ip), nicotine (0.2 mg/kg, sc), or saline, and locomotor activity was measured for 1 hr. Locomotor responses to amphetamine and to nicotine were significantly greater in rats preexposed to brain stimulation. These findings suggest at least partial overlap of underlying substrates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical self-stimulation and its theoretical implications.

Evidence from electrical self-stimulation experiments is reviewed in the light of Deutsch's structural theory of behavior. The theory accounts for all salient observations; viz., high drive, little or no satiation, rapid extinction, the need for "priming" at the start of a day's trials, the difficulty in creating secondary reinforcers by using electrical stimulation of the brain as a primary reinforcer, the fact that different electrode placements interact with different natural drives, and the separability of the motivation and reinforcement processes. Other theories are briefly reviewed. (46 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Poststimulation excitability of ventral pallidum self-stimulation neurons.

The degree of neural recovery from refractoriness was inferred in rats self-stimulating with pairs of pulses in the ventral pallidum. The prerecovery intrapair interval varied from 0.5 to 1.0 ms, depending on brain site. At some sites, recovery reached its maximum within less than 1.6 ms whereas, at the majority of sites, a substantial amount of recovery occurred at delays longer than 1.2 ms. The shortest recovery estimates were not fundamentally different from those obtained from sites lying along the medial forebrain bundle. The longest recovery estimates were similar to those obtained from cortical and basal forebrain sites. The differences in recovery noted between sites and the presence of step-like patterns in the recovery curves suggest the presence of neural heterogeneity within the ventral pallidal substrates of reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for a role of dopamine in self-stimulation of the nucleus accumbens of the rat.

Investigated the effects of centrally administered spiroperidol, a dopamine receptor blocking agent, on self-stimulation of the nucleus accumbens and medial prefrontal cortex in the rat. Spiroperidol in a volume of 1 μl was microinjected into the region of the stimulating electrodes. Self-stimulation of the nucleus accumbens was significantly attenuated by .75, 1.0, and 2.0 μg spiroperidol. Control microinjections of the drug vehicle had no effect. Spiroperidol microinjected into the nucleus accumbens contralateral to the stimulating electrode, as a control for possible motor or nonspecific effects, did not attenuate self-stimulation. Microinjections of spiroperidol into the region of the stimulating electrodes in the prefrontal cortex had no consistent effect on self-stimulation with the two lower doses, but did result in attenuation at the 2.0 μg dose. Self-stimulation of the nucleus accumbens was not changed by microinjections of spiroperidol into the ipsilateral or contralateral prefrontal cortex. Similarly, self-stimulation of the prefrontal cortex was not altered by microinjections of spiroperidol into the nucleus accumbens. By controlling for nonspecific effects of spiroperidol, the results provide further evidence that dopaminergic neurons contribute to self-stimulation of the nucleus accumbens. (French summary) (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Empathy: A physiological substrate.

Studied the relation between empathy (defined as the ability to perceive accurately how another person is feeling) and physiology in 31 Ss. Ss viewed 15-min marital interactions and used a rating dial to indicate continuously how they thought a designated spouse was feeling. Rating accuracy was determined by comparing Ss' ratings with identical self-ratings obtained previously from the target spouse. Physiological linkage between S and target was determined using bivariate time-series analyses applied to 5 autonomic and somatic measures obtained from the S during the rating task and from the target spouse during the original conversation. Accuracy of rating negative emotion was greatest when S and target evidenced high levels of physiological linkage across time. Accuracy of detecting positive emotion was related to a state of low cardiovascular arousal in the S, but not to physiological linkage between S and target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral measurement of the neural refractory periods for stimulus-bound eating and self-stimulation in the rat.

Subjected 4 albino Sprague-Dawley rats to electrical brain stimulation in pulse pairs. The duration of stimulus-bound eating and rate of self-stimulation were each measured as functions of intrapair interval (IPI). Eating increased sharply when the IPI exceeded .6-.8 msec, and self-stimulation increased when the IPI exceeded .8-1.2 msec. These values are interpreted as the refractory periods of the directly stimulated neurons involved in those behaviors. As the same Ss were used for both experiments and other stimulus parameters were comparable, it is concluded that different sets of neurons are involved in the 2 behaviors. In a 3rd experiment, food deprivation increased the rate of self-stimulation for 1 S, but not for the other 3. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis and chromatographic properties of cysthationamine. A substrate for diamineoidase

Details are reported for the preparation of the 2-aminoethyl, 3-aminopropyl sulfide from 3-bromopropylamine and 2-mercaptoethylamine. For this compound, the shorter name cystathionamine is proposed. The corresponding sulfoxide and sulfone have been also prepared. Some analytical data and chromatographic properties are reported. Preliminary results show that cystathionamine is a good substrate for the pig kidney diamineoxidase.     

Fitting intracranial self-stimulation data with growth models.

Until now, the problem of fitting self-stimulation rate-frequency functions has been dealt with by using linear models applied to the linear portion of the empirical curve. In this article, an alternative procedure is presented, together with three sigmoid growth models that seem to accurately fit rate-frequency data. From any of these models, it is possible to compute the two indices of stimulation efficacy in use in the parametric study of brain stimulation reward (M?? and θ?), in addition to the inflection point of the curve, which can be used as an alternative to M??. Important relations allowing initial estimation of each parameter are provided, allowing use of computer programs derived from the Gauss-Newton algorithm for nonlinear regression. The considerations relevant to the choice of a nonlinear model are discussed in terms of each efficacy index. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Integration of free pulses in electrical self-stimulation of the rat brain.

Frequency thresholds for electrical self-stimulation of the medial forebrain bundle were estimated in rats while low frequencies of pulses were applied continuously. When continuous pulses were delivered to the same electrode that received the 0.5-sec trains of response-initiated stimulation, thresholds decreased by the free-pulse frequency (Experiment 1), consistently across current (Experiment 2). Estimates of the reward added by concurrent, response-contingent stimulation of the opposite electrode of a bilateral pair predicted the drop in threshold caused by the noncontingent pulses applied to the opposite hemisphere (Experiment 3), again, robustly across test current (Experiment 4). Continuous pulses restricted to times between self-initiated trains lost their effect (Experiment 5). The perception of reward was invariant despite changes in the overall activity of the self-stimulation substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of retention by self-stimulation and by experimenter-administered stimulation.

73 male hooded rats were trained on a 1-trial appetitive learning task, given various posttraining brain stimulation treatments of the lateral hypothalamus, and tested for retention 24 hrs later. Posttraining trial treatments of 1,000 trains of self-stimulation or 30 trains of experimenter (E)-administered stimulation facilitated retention. Treatments of 1,000 trains of E-administered stimulation or 30 trains of self-stimulation did not facilitate retention. Two possible hypotheses are discussed as explanations of this pattern of results. The concept of reinforcement from an optimum level of arousal can explain the data, if it is assumed that a self-stimulating rat regulates its rate of responding so as to control its own level of arousal. Alternatively, the facilitation of retention by 1,000 trains of self-stimulation and by 30 trains of E-administered stimulation may each represent the function of an independent neural substrate of reinforcement, each with its own set of requirements for activation. (French summary) (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anatomical dissociation of the substrates of medial forebrain bundle self-stimulation and exploration.

The purpose of this research was to determine whether brain stimulation reward and exploration are induced by activation of the same set of neurons along the medial forebrain bundle. The behavioral version of the collision test was utilized with electrodes in the lateral hypothalamus (LH) and the ventral tegmental area (VTA). A collision effect obtained between LH and VTA in one behavior at the exclusion of the other was treated as evidence of the involvement of two different sets of fibers. In 4 rats, a collision effect was observed only in self-stimulation, whereas in 1 rat, a collision was obtained in exploration at the exclusion of self-stimulation. Three animals showed no collision in either behavior. These data suggest that coexistence of self-stimulation and exploration following medial forebrain bundle stimulation can be explained by current spread on two different sets of fibers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration in self-stimulation: A paradox lost?

Seven self-stimulating rats with electrodes located along the medial forebrain bundle were used to study how excitation dissipates at the end of a train of rewarding electrical pulses. On a 5-s, fixed interval (FI) schedule, the rats pressed a lever to obtain 2 trains of pulses separated by gaps of up to 2 s; the first train was fixed at a just-subthreshold number of pulses, whereas the second train was used to scale the number of pulses needed to just support consistent responding. The number of pulses needed grew with increasing gaps between the 2 trains, rapidly at first and then decelerating to an asymptote, with time constants of a few tenths of a second. These results support C. R. Gallistel's (1974, 1978) model of leaky integration of rewarding brain stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhancement and suppression of self-stimulation after ventromedial hypothalamic lesions.

Investigated the effects of lesions in the ventromedial hypothalamus (VMH) upon self-stimulation in 25 male hooded Long-Evans rats. Ss trained to press a bar for lateral hypothalamic (LH) stimulation showed an enhancement of responding during the 1st 24 hrs after VMH lesioning, followed by a suppression of responding for several days. The degree of response suppression, but not enhancement, was correlated with an increase in food intake. In Ss trained to shuttle for LH stimulation, only the suppression effect was observed after VMH lesions. Barpressing for dorsal tegmental stimulation was not affected by the lesions. Results suggest that LH stimulation activates at least 2 groups of neurons: one group is specifically involved in barpressing and the other is involved equally in barpressing and shuttling. (French summary) (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of cholinergic agonists and antagonists on self-stimulation behavior in the rat.

Trained 23 male Wistar albino rats to press a bar for electrical stimulation of the brain on a 30-sec variable-interval schedule. Ss were tested weekly with 1 or more of the following drugs: physostigmine (50-400 MUg/kg), neostigmine (25-200 MUg/kg), atropine (2-16 mg/kg), methylatropine (2-16 mg/kg), scopolamine (400-1,600 MUg/kg), pilocarpine (500-4,000 MUg/kg), nicotine (100-800 MUg/kg), mecamylamine (1 mg/kg), and methamphetamine (500 MUg/kg). Results support the suggestion that the cholinergic system is composed of 2 reciprocally related components: (a) a muscarinic "no-go" portion, whose activation has an inhibitory effect on self-stimulation; and (b) a nicotinic "go" portion, whose excitatory effect on self-stimulation is (most probably) mediated by norepinephrine. (33 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)