Unsignalled Shock Research Articles

Contextual Fear after Signalled versus Unsignalled Shocks: Effect of Extent of Prior Experience with Context and Signal

In the first two experiments, rats were differentially familiarized with a discrete stimulus and/ or a context prior to receiving either shocks signalled by that stimulus or unsignalled shocks in that context. As indexed by freezing, in none of the pre-exposure conditions did the signalled-shock rats consistently acquire less contextual fear than the unsignalled-shock animals. Both pre-exposure to the stimulus and relatively short pre-exposure to the future conditioning context resulted in more contextual fear in the signalled-shock than in the unsignalled-shock subjects. In a third experiment, freezing in the target conditioning context was especially enhanced in rats that had been familiarized with a stimulus, conditioned with the stimulus as a signal for shock, and subsequently further conditioned to the stimulus in a different, non-target context. The level of freezing to the stimulus in a neutral test context was positively related to the level of freezing in the target conditioning context in all ex...

Effects of signalling parameters on human electroshock perception: Informational control versus stimulus error

Informational Control theories predict that (a) a signal preceding a noxious, unavoidable stimulus will reduce the perceived intensity of that stimulus, and (b) it is the information provided by the signal that is responsible for this effect. In the present experiment, the first prediction was evaluated by presenting all subjects with a series of shocks under a signalled condition (light signal preceding shock onset), and two types of unsignalled conditions (light and shock simultaneous, and no light The second prediction was tested during the signalled trials by varying the information provided by the light signal: subjects were divided into four groups, and each group received high or low amounts of temporal and contingency signal information. Neither prediction was supported & the results: (a) a signal preceding the shock did not affect the perceived intensity; (b) subjects magnitude estimations of perceived shock intensity also yielded no significant effects of signal information. However, unsignalled shocks which occurred simultaneously with the light were rated significantly higher in intensity than either the signalled shocks or the unsignalled shocks which were not accompanied by a light. This suggests that simultaneous light signal + shock is an inappropriate control for testing hypothesis (a). We speculate on the reasons for this problem.

Stressor predictability and rat brain noradrenaline metabolism

This study examined the effects of stressor predictability on regional rat brain noradrenaline (NA) turnover, by measuring levels of a principal metabolite of NA (3-methoxy-4-hydroxyphenylenhyleneglycol sulfate, MHPG-SO 4). Male Wistar rats were exposed to one of three shock conditions for 19 hr: nonshock, signalled, and unsignalled shocks. Rats in the shock conditions received shock (1.2 mA intensity, 2 sec duration) on a 2.5 min variable time (VT) either preceded by a 12-sec, 10-W light signal (signal-shock interval of 10 sec) or not preceded by this signal. The tail electrodes for these rats were in series, so that the shock received by all rats was of exactly the same number and duration. After 19 hr in a VT-2.5 min shock session, the rats exposed to unsignalled shock (unpredictable group) showed significantly greater increases in MHPG-SO 4 levels in the hypothalamus, amygdala, midbrain, cerebral cortex, thalamus and locus coeruleus, as well as in plasma corticosterone levels. Rats exposed to signalled shock (predictable group) showed significant increases in MHPG-SO 4 levels in the first four of these regions, as compared to the nonshocked rats. Moreover, the unpredictably shocked rats exhibited greater elevations in MHPG-SO 4 levels in the hypothalamus, amygdala, and thalamus, as well as in plasma corticosterone levels, when compared to the predictably shocked rats. These results are consistent with previous reports showing that unsignalled shock induced extensive somatic effects in comparison to signalled shock. The present study suggests that the presence of a signal attenuates the extent of NA release in some brain regions resulting from irregular inescapable shock stress.

Effects of piracetam on learned helplessness in rats

In rats, the effects of Piracetam (P), the prototype of nootropic drugs, were studied on a very widely used model of behavioral disturbance: the learned helplessness (LH) phenomenon. In this model, exposure to uncontrollable and unsignalled shocks impairs subsequent escape-avoidance learning. In a first experiment, this deficit was abolished by 200 mg/kg of P, and to a lesser extent, by a 100 mg/kg dose, administered before the training session. In non-stressed animals, no dose of P was able to have a facilitatory effect on escape-avoidance. In a second experiment, the administration of P, not before the training session as in Experiment I, but before the stress, had no effect on the LH phenomenon regardless of the dose.

Somatomotor thresholds in the New Zealand albino rabbit in response to paraorbital electric shock.

A procedure for assessing objectively unconditioned responses to paraorbital electrical shock is described. Using the method of constant stimuli human observers can reliably detect “eye twitch”, “eyeblink”, and “jump” responses when a brief unsignalled paraorbital shock is presented.

Interactions amongst factors which influence severity of gastric ulceration in rats

A number of factors have previously been demonstrated to influence the severity of stress-induced gastric ulceration in rats, including prior exposure to pre-shock and allowing animals a post-stress rest or recovery period. The primary purpose of this experiment was to investigate how one of these factors might modulate the expression of the other. Animals were pre-exposed to either signalled or unsignalled shock (using “learned helplessness” parameters), or no shock. They were later subjected to 2 hours restraint-in-water (immersion) stress, or appropriate handling control procedures. Half of the animals were sacrificed immediately on removal from the water-restraint, and half were sacrificed after a 2 hour recovery period in their home cages. Analysis of the severity and number of glandular stomach lesions indicated that animals subjected to the pre-shock exhibited greater ulceration than unshocked animals, as long as no post-stress rest period was allowed. Additionally, the effect of post-stress rest was masked by experience with pre-shock. This reciprocal modulation of treatment influences may offer suggestions for understanding discrepancies in the literature on the effects of these two modulating variables.

A New Shock Delivery Method for Testing Preference for Signalled Shock

We present a method for delivering tail shock in which the electrodes cannot be dislodged and which allows the rat a full range of ambulatory behaviors. Using this method in a shuttle box environment, we have shown that a significant number of rats consistently prefer signalled over unsignalled shock.

Effects of Signalled and Unsignalled Electric-Shock Delivery on Schedule-Controlled and Schedule-Induced Behavior

In Experiments 1 and 2, food pellets were delivered under a fixed-interval (Fi) 40-sec. schedule, with water freely available in an operant chamber. After acquisition of stable levels of lever pressing and schedule-induced water intake, electric shock was introduced under a variable-time (Vt) 70-sec. schedule. Each of four rats was studied under signalled and unsignalled electric shock. During signalled shock delivery, a 10-sec. stimulus preceded each shock. During unsignalled shock delivery, the preshock stimulus was not presented. More suppression of lever pressing was found for all of the animals during unsignalled than signalled shock. Three of four animals also suppressed schedule-induced licking more during unsignalled than signalled shock. For both lever pressing and licking, response suppression was a function of the intensity of shock. Depending upon the intensity of shock, responding was (a) relatively unaffected during signalled and unsignalled shock, (b) suppressed primarily during unsignalled shock, or (c) markedly suppressed under signalled as well as unsignalled shock. In Experiment 3, food pellets were delivered under a fixed-time (Ft) 40-sec. schedule. Schedule-induced licking was studied under signalled and unsignalled Vt 70-sec. shock delivery. More suppression of schedule-induced licking occurred during unsignalled than signalled shock for all of the animals. These data show that schedule-induced licking, like food-maintained lever pressing, is suppressed more by unsignalled than by signalled shock delivery.

The preference-for-signalled-shock phenomenon: Reliability and sensitivity of asymmertical and symmetrical changeover procedures in the skinner box

Abstract The reliability and sensitivity of changeover for signalled inescapable shcok was assessed in seven experiments. Evidence from Experiments la-ld showed that the asymmetrical changeover preparation (ACP) intended to measure preference for signalled to unsignalled shock was not reliable in that a marked and stable changeover for signalled shock could be obtained in only 1 of 24 rats tested. Evidence from Experiment le that rats would not even readily changeover from shock to no shock further indicated that the ACP is an inadequate method for evaluation preference. Experiment IIa employed a significantly more sensitive symmetrical changeover preparation (SCP) wherein preferenc for low over high intensity shock was found, but Experiment IIb, using SCP found that rats are indifferent to a choice between signalled and unsignalled inescapable shock.

Effects of the Intensity of Electric Shock on Response Suppression During Multiple and Mixed Schedules of Signalled and Unsignallei Electric-Shock Delivery

In three experiments, food-rein forced responding was studied during multiple schedules of signalled and unsignalled electric-shock delivery. Depending upon the shock intensity employed, responding was (a) similarly suppressed in each component, (b) reduced primarily in the component associated with unsignalled shock, or (c) reduced considerably in both components of the multiple schedule. Mild shock intensities, which initially failed to produce differential response suppression, did so when they were reintroduced following exposure to more intense signalled and unsignalled shock. Food-maintained responding was studied during mixed as well as multiple schedules of signalled and unsignalled electric-shock delivery in Experiment 3. During the mixed schedules of food-and-shock delivery, the components were not distinguished by correlated stimuli, remaining either light or dark. While the multiple schedule readily led to differential response suppression, similar levels of response suppression were found in both components during the mixed schedule of signalled and unsignalled shock delivery. These experiments show that differential response suppression during signalled and unsignalled shock is a function of shock intensity and the discriminability of shock and shock-free occasions.

A TEMPORAL PARAMETER INFLUENCING CHOICE BETWEEN SIGNALLED AND UNSIGNALLED SHOCK SCHEDULES1

The present study investigated whether choice of a signalled variable-time shock schedule over an unsignalled one was influenced by the average intershock interval. Eight rats were given a choice between signalled and unsignalled shock schedules in a series of conditions with average intershock intervals of 510, 270, 150, 90, 60, and 45 sec. Each test condition was preceded by a training-baseline condition, and schedule values were arranged in an ascending (four subjects) or descending (four subjects) order. Choice of the signalled conditions was directly related to the average intershock interval of the variable-time schedule for six of the eight subjects. The per cent of time in the signalled condition was highest when the average intershock interval was 150 sec or longer and lowest when the average intershock interval was 45 sec. The findings were interpreted as being due to changes in the safety features of the signalled schedule, rather than to changes in the average intershock interval per se.

CHOICE FOR SIGNALLED OVER UNSIGNALLED SHOCK AS A FUNCTION OF SHOCK INTENSITY1

Choice between a signalled shock schedule and an unsignalled one was examined at various shock intensities. Three rats were given the opportunity to change from the unsignalled schedule to the signalled one at intensity values between 0.15 mA and 1.0 mA. Steps were usually 0.15 mA and both ascending and descending series were given. For two other rats, shock intensity increased from 0.20 mA to 1.0 mA in 0.20-mA increments; for two additional rats, shock intensity was first 3.0 mA and was then reduced to 1.0 mA. Subjects tended to remain in the unsignalled schedule at the lower shock intensities, but spent most of each session under the signalled schedule at the higher intensities (1.0 mA and 3.0 mA). In addition, the time spent in the signalled schedule tended to vary systematically with shock intensity over at least part of the range of intensity values. It was concluded that the relationship between shock intensity and choice behavior is similar to the relationship between intensity and behavior in procedures involving avoidance, escape, and punishment.

An Application of the Species-Specific Defense Reaction Hypothesis

Acquisition of lever pressing by rats required to escape and avoid unsignalled shock in a test chamber equipped with 2 response levers was examined. Similarity of the arbitrary lever press to one of the S’s species-specific defense reactions (SSDR) to shock —flight—was manipulated by raising and lowering sliding hatches directly above and behind each response lever. Specific sequences of manipulating abortive escape routes proved critical, but results generally support Bolles’ assertion that learning an avoidance response is facilitated if the required response is a SSDR to the aversive stimulus —or at least closely resembles one. In addition, data on escape and avoidance lever-holding during successive portions of the session verify, with only minor qualification, Bolles’ account of the importance of freezing, another Ssdr, in the acquisition of the lever-press avoidance response.

CHOICE OF HIGHER DENSITY SIGNALLED SHOCK OVER LOWER DENSITY UNSIGNALLED SHOCK1

Unsignalled, inescapable shocks were presented to four albino rats in Experiment 1. By pressing a lever subjects could change the condition to signalled shock for 3-min periods after which unsignalled shock was automatically reinstated. All subjects changed from unsignalled to signalled shock when shock density was the same or when the density of signalled shock was two times greater than unsignalled shock. When the density of signalled shock was four times that of unsignalled shock, three subjects changed to the higher density schedule. One subject changed to a density of signalled shock eight times that of unsignalled shock. The second study showed that the two shock schedules most similar in Experiment 1 were discriminably different because subjects chose lower over higher shock densities when both densities were unsignalled. An analysis stressing safe (signal absent) and unsafe (signal present) periods was discussed.

CHOICE OF LONGER OR STRONGER SIGNALLED SHOCK OVER SHORTER OR WEAKER UNSIGNALLED SHOCK1

Unsignalled, inescapable shocks were presented to four albino rats in one study and to six rats in a second study. By pressing a lever, subjects could change the condition to signalled shock for 3 min after which unsignalled shock was automatically reinstated. All subjects changed frequently to the signalled shock schedule. After a minimum of three 6-hr sessions or after changeover responding stabilized at the previous values, higher values of signalled shock intensity or duration were introduced. In the first study, the duration of signalled shock was increased in increments of 0.5 sec. In the second study, the intensity of signalled shock was increased in increments of either 0.2 or 0.4 mA. Duration subjects chose signalled shock four (2.0 sec) to nine times (4.5 sec) longer than unsignalled shock (0.5 sec). Intensity subjects chose signalled shock two (2.0 mA) to three times (3.0 mA) more intense than unsignalled shock (1.0 mA).

A RATE MEASURE OF THE RELATIVE AVERSIVENESS OF SIGNALLED VS UNSIGNALLED SHOCK1

Five rats were trained on a two-component multiple schedule with each component consisting of a two-link chain schedule. Differential response suppression in the initial links of the chain schedules was used as a measure of the relative aversiveness of events introduced into the subsequent terminal links. When unsignalled shock was scheduled in one terminal link and signalled shock in the other (in addition to equal numbers of food reinforcers), responding was suppressed to a greater degree in the initial link preceding the unsignalled-shock condition. Reversing the terminal-link positions of unsignalled shock and signalled shock led to a reversal of the differential response suppression in the initial links. These results confirm previous findings that signalled shock is less aversive than unsignalled shock and extend the generality of this phenomenon from choice measures to rate measures of aversiveness.

Vicarious conditioned acceleration: successful observational learning of an aversive Pavlovian stimulus contingency.

Five rats (observers) were trained to avoid unsignalled shocks in a shuttlebox and then habituated to brief light presentations. They were next confined on an observation platform while another rat (model) received light-shock pairings in the opposite compartment. The observers were exposed only to the sight and sound of the model during classical conditioning and were not shocked themselves. Test presentations of the light during subsequent avoidance sessions produced response rate increases (vicarious conditioned acceleration) comparable to those obtained in other studies where the avoidance animals were used in classical conditioning. Following sessions in which the model was not shocked after the light, the light presentations during avoidance eventually failed to elicit any response increases in the observers. When the model was again shocked, immediate recovery of avoidance acceleration occurred in the observers during the light.

IN COMPATABILITY BETWEEN THE PIGEONS' UNCONDITIONED RESPONSE TO SHOCK AND THE CONDITIONED KEY‐PECK RESPONSE1

High-speed photography was used to compare the pigeon's response to unsignalled shock with the pigeon's key-peck response. During shock, pigeons flex their neck (i.e., the distance between their eyes and shoulders decreases). Following shock, the neck is extended. During key pecking, the neck remains extended and the head moves toward the key in a slight arc as though attached to a fixed fulcrum. Response topography during pecking and shock appear to be incompatible, and it is concluded that the difficulty in key-peck training pigeons to escape electric shock is due to interference from the unconditioned flexion response. This conclusion supports the species-specific defense theory of escape and avoidance behavior.

THE RESPONSE‐SHOCK—SHOCK‐SHOCK INTERVAL AND UNSIGNALLED AVOIDANCE IN GOLDFISH1

Goldfish were trained to swim back and forth in a shuttle tank to avoid unsignalled shocks. The response-shock interval and the shock-shock interval were always of equal duration; both were either 15, 30, 45, or 60 sec. Response rates varied inversely with response-shock-shock-shock interval duration, as has been found with rats. Percentage of shocks avoided was somewhat lower at the 15 sec response-shock-shock-shock interval, but otherwise did not vary systematically with changes in the interval. As the response-shock-shock-shock interval increased, the fish made increasingly more responses than necessary to avoid all shocks. Interresponse-time distributions showed that response probability rose to a maximum at about 15 to 25 sec after a response, regardless of the response-shock-shock-shock interval. Thus, at the longer intervals the fish were responding too early in the response-shock-shock-shock interval to minimize response rates.

Adrenocortical activity and avoidance learning as a function of time after fear conditioning

Shuttlebox avoidance learning in rats is a U-shaped function of time after fear conditioning. The descending limb of the function was found to be correlated with a corresponding decrease in plasma concentration of corticosterone, and it is suggested that the ascending limb of the function may be associated with an increasing sensitivity of the adrenocortical system over time. Unsignalled shock does not produce the U-shaped function but does produce changes in steroid concentration similar to those initiated by fear conditioning.