Escape behavior under different fixed ratios and shock intensities

The effects of ratio length and shock intensity on bar pressing were examined in three rats in two escape-from-shock experiments. In Experiment I, shock intensity was held constant while the schedule was varied from FR 1 to FR 20. The latency of the first escape response increased with FR length while the escape rate, computed as over-all rate in shock minus latency of the first response, decreased at FR 20. In Experiment II, the schedule was held constant at FR 5 while shock intensity was manipulated. Latency decreased as intensity increased, while escape rate increased with intensity, passing through a maximum for two subjects. Responses occurring during the last 100 sec of the 2-min escape period decreased as the FR increased for all subjects, and decreased as shock intensity increased for two subjects.     

Escape responding in a shuttlebox

Measures of response latency are a primary tool for those who investigate escape responding in rats. Unfortunately, the single term “latency to escape” has been applied to several different measures of latency. The present study was designed to demonstrate that two different measures of the “latency to escape” tap different aspects of escape responding. To that end, rats were given escape training using a Sidman Avoidance Schedule with brief inescapable electric shock as the aversive stimulus. The latency to escape the shock-shock interval, as measured from the onset of the last shock in a shock period, did not change across trials. However, the latency to escape the shock period, as measured from the onset of the first shock in a shock period, decreased across trials. In addition, the presentation of a feedback stimulus contingent upon escape responding did not affect the latency to escape either the shock period or a shock-shock interval. The results show that these two latency measures, typically not recognized as unique, measure different characteristics of the strength of escape responding in a shuttlebox. Alternative accounts of this pattern of data were considered.     

Effects of reserpine on retention of escape reversal in mice: absence of state-dependent learning.

A discriminated escape training paradigm was used to study the effects of reserpine on learning and memory in mice. Intraperitoneal injection of reserpine before reversal training had no effect on acquisition but did produced a time-and dose-dependent impairment of retention test performance 10 days later. These results suggested that reserpine may have interfered with some aspect of memory storage. Retention impairments observed when a 2.0 mg/kg reserpine injection was given 2 hr before reversal training were not attenuated by readministering the drug before testing, a finding that provides no support for a state-dependency interpretation. Furthermore, animals treated with reserpine exhibited inferior retention of previous training, regardless of the pharmacological state present during that learning. This was interpreted as a drug-induced impairment of memory retrieval. In addition, performance during the initial discriminated escape training session suggested that reserpine may also impair acquisition under some conditions. In the last experiment, it was found that when the catecholamine precursor L-dihydroxyphenylalamine (100 mg/kg) and the indole amine precursor D,L-5-hydroxytryptophan (125 mg/kg) were both given after reserpine treatment, subsequent retention performance was not significantly impaired. The results are discussed in terms of the possible roles of biogenic amines in arousal, learning, and memory.     

Enhanced visuospatial memory following intracerebroventricular administration of nerve growth factor

The present work assessed the effects of intracerebroventricular injections of rh recombined human nerve growth factor (rh NGF) (5 micrograms/2.5 microl) at postnatal days 12 and 13 upon the development of spatial learning capacities. The treated rats were trained at the age of 22 days to escape onto an invisible platform at a fixed position in space in a Morris navigation task. For half of the subjects, the training position was also cued, a procedure aimed at facilitating escape and at reducing attention to the distant spatial cues. Later, at the age of 6 months, all the rats were trained in a radial-arm maze task. Treatment effects were found in both immature and adult rats. The injection of NGF improved the performance in the Morris navigation task in both training conditions. There was a significant reduction in the escape latency and an increased bias toward the training platform quadrant during probe trials. The most consistent effect was the precocious development of an adult-like spatial memory. In the radial-arm maze, the NGF-treated rats made significantly fewer reentries than vehicle rats and this effect was particularly marked in the treated female rats. Taken together, these experiments reveal that the development and the maintenance of an accurate spatial representation are tightly related to the development of brain structures facilitated by the action of NGF. Moreover, these experiments demonstrate that an acute pharmacological treatment that leads to a transient modification in the choline acetyltransferase activity can induce a behavioral change long after the treatment.     

Improvement in memory with time

Groups of rats which had incompletely learnt to escape from shock into the lit arm of a Y-maze, were tested for retention of the habit at various times after training. These times ranged from 30 min. to 17 days. Retention was found to be poor from 30 min. to 5 days, showed a marked improvement at 7 to 10 days and a subsequent decrement after 14 days. These results parallel those previously found for the differential susceptibility to cholinergic drugs of habits of different age. They provide further evidence that memory strength increases with time up to a point, and then gradually decreases.     

Predictability,controllability, and inoculation against learned helplessness

Nondepressed human subjects were divided into seven groups. On a series of discrimination problems, a helplessness group received insoluble problems, a solvable group received contingent feedback, and a no treatment control group received no feedback. For two other groups insoluble problems were preceded by success feedback on a different task presented according to a fixed ratio (FR) or variable ratio (VR) schedule of reinforcement. Two control groups received either FR or VR schedules of success but were not examined on the discrimination problems. All groups were tested for escape/avoidance performance on a human shuttle box. Both FR and VR schedules produced an inoculation against learned helplessness; escape performance by the helplessness group was significantly worse than that of FR and VR inoculation groups. These latter groups performed similar to the solvable and three control groups. Significantly worse than that of FR and VR inoculation groups. These latter groups performed similar to the solvable and three control groups. Significantly fewer subjects in the VR inoculation group exhibited avoidance responses than their counterparts in the FR inoculation group. despite similar escape performance. The findings indicate that learned helplessness can be prevented in humans and suggest different sources of interference produced by unpredictable and uncontrollable events.     

Spatial learning in a T-maze by the crayfish Orconectes rusticus

The T-maze has commonly been used to investigate the mechanisms underlying spatial learning in vertebrates and has yielded much information about how animals use response and place cues to orient toward a goal. We designed a T-maze to study the spatial learning abilities of crayfish (Orconectes rusticus), using tactile stimuli as a place cue and escape from warm water for reinforcement. An initial experiment found that most animals did not display a side-turning bias when first placed in the maze, and hence animals were randomly assigned to escape from the left or the right arm, one of which contained a smooth floor and the other a rough floor. We found that, over repeated trials, the latency to escape and the number of turns made prior to escaping significantly decreased indicating that crayfish learned to escape from the maze more rapidly and efficiently. Learning occurred over the course of six trials on a single day, and over 5 days of testing, providing evidence for spatial memory lasting 24 hr. In probe trials, in which experienced animals started the maze in an arm opposite to that used during training trials, crayfish did not display a preference for either response-based learning or place-based learning. Instead they engaged in renewed exploration of the entire maze. These findings suggest that, in addition to remembering the location of the exit, crayfish also remembered the overall configuration of the maze.     

Glucose effects on memory: behavioral and pharmacological characteristics

Recent findings indicate that post-training glucose injections can modulate memory storage for inhibitory (passive) avoidance training. Experiment I extended these findings to determine whether glucose, like other memory modulating treatments, enhances memory storage when administered after training with low footshock and impairs memory storage after high footshock training. In Experiment I, male Sprague-Dawley rats were trained in a one-trial inhibitory avoidance task using either a brief footshock (0.5 mA, 0.7 s) or slightly more intense footshock kept on until escape (0.7 mA, mean escape latency = 3.4 s). Immediately after training, each rat received a subcutaneous injection of glucose (100 mg/kg). When tested for retention performance 24 h later, the glucose-injected animals exhibited enhanced retention performance for low footshock training and impaired retention for high footshock training. Experiment II determined whether pretreatment with adrenergic antagonists blocked the effects of glucose on memory. Pretreatment with the alpha- or beta-adrenergic receptor antagonists, phenoxybenzamine, or propranolol, respectively, had no effect on acquisition or retention in animals trained with the brief footshock and did not affect glucose facilitation of that memory. In animals trained to escape footshock, phenoxybenzamine did not attenuate the amnesia produced by glucose. Propranolol-pretreated animals had impaired retention whether or not they received post-training amnestic injections of glucose; glucose had no effect on retention in these amnestic animals. These findings add further support to the view that glucose release after training and treatment may represent a physiological response subsequent to epinephrine release in modulating memory storage processing.     

Spatial behavior in male and female crayfish (Orconectes rusticus): learning strategies and memory duration

Previous studies have demonstrated that animals use multiple strategies to solve spatial tasks. We used a T-maze to examine spatial behavior in crayfish, using visual and tactile stimuli as place cues and a food-scented escape tank as reinforcement to leave the maze. In trials on a single day and across multiple days, crayfish learned to exit the maze with significantly reduced latency and with fewer turns. In addition, we examined place memory in 40-min periods with the maze closed and found that crayfish spent longer in the vicinity of a previously open exit compared to a closed exit. Probe tests were conducted using a forced-choice procedure to determine whether crayfish remembered the route out of the maze using primarily place cues or response learning. We found that approximately equal numbers of animals used each strategy, and individuals were able to switch from one strategy to the other on different test days. Males and females did not differ significantly in their performance in the place memory test, maze exit task, or probe tests. Both sexes displayed place memory for the exit location and reduced latency to exit during trials 24 h, 48 h, 72 h, and 1 week after initial training trials, suggesting that spatial memories in crayfish are relatively enduring.     

Context Shift and Protein Synthesis Inhibition Disrupt Long-Term Habituation after Spaced,but Not Massed,Training in the CrabChasmagnathus

An opaque screen moving overhead elicits an escape response in the crabChasmagnathusthat after a few presentations habituates for a long period (long-term habituation, LTH). Previous results suggested that spaced (15 trials separated by 171 s) and massed training (300 trials without rest interval) were correlated with two different memory components of LTH. The present experiments were aimed at further studying the mechanisms subserving these components. Results indicate that LTH acquired by spaced but not by massed training is blocked either by a training-to-testing context shift or by cycloheximide (15–25 μg) pre- or posttraining injection and that LTH after spaced training persists for longer time (5 days) than after massed training (2 days). A model based on these results that distinguishes two LTH-memory components is proposed: a (context-signal) LTH yielded by spaced training, dependent of context, sensitive to cycloheximide (CYX), and long lasting; and a (signal) LTH yielded by massed training, dependent only on the signal invariance, insensitive to CYX, and shorter lasting.     

Behavioural inhibition and the age at social isolation in rats

Rats that were socially isolated or group-housed at weaning were re-housed at 51 days of age in either the same housing condition or the opposite housing condition until 91 days and throughout subsequent behavioural testing. Increased resistance to extinction of running in an alley and poorer Hebb-Williams maze learning were found only after social isolation between 23 and 51 days of age. In contrast, slower running to reach the water reward during alley training and lower rearing activity at the beginning of open field testing were evident only in rats that were isolated at the time of testing. As in previous studies, open field hyperactivity was found in rats isolated at weaning but slower emergence latency was found in animals isolated at the time of testing. These findings confirm that the many behavioural effects of social isolation at different ages do not reflect a unitary aetiology. The behaviour of rats isolated at weaning is suggestive of a “disinhibition syndrome” but the precise nature of this syndrome is as yet unclear.     

Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.     

A room with a view and a polarizing cue: individual differences in the stimulus control of place navigation and passive latent learning in the water maze

We investigated individual differences in the stimulus control of navigational behavior in the water maze by comparing measures of place learning in one environment to measures of latent learning (via passive placement on the goal platform) in a novel environment. In the first experiment, 12 rats were trained to find a slightly submerged hidden platform at a fixed location in room A for 10 days (4 trials/day). Fast and slow place learners were identified by their mean escape latency and cumulative distance to the goal during acquisition. The same animals were then given a 2-min passive placement on the submerged platform in room B. Latent learning was assessed by the animal's escape latency on a single swim trial immediately following the placement in room B. The results showed that the good latent learners in room B were not necessarily the fast place learners in room A. This weak correlation may be related to the fact that some rats swam near the area in room B that corresponded to the former goal location in room A relative to a common polarizing cue (i.e., the door/entrance to both rooms). When the view of the door was blocked in a second experiment a significant positive correlation between place acquisition and the latent learning test was obtained, although escape performance following passive placement was not improved. These findings suggest that while place navigation and latent learning via passive placement may involve some common cognitive-spatial function, other associative (S-S and/or S-R) processes that occur during place navigation/active movement may be required for animals to exhibit truly accurate navigational behavior characteristic of asymptotic escape performance in the water maze. Additional implications for neurobiological studies using a procedural pretraining design are discussed.     

Effect of ventromedial hypothalamic procaine injections on feeding, lever pressing, and other behavior in rats.

Rats were given bilateral injections of 1-2 mul procaine HCl solution (50 mug/mul) in the region of the ventromedial hypothalamus. Normal-sized meals occurred reliably with a latency of 16-120 sec, indicating that this region has the function of inhibiting onset of eating, not just the function of stopping a meal. Food-rewarded fixed-ratio-of-one (FR 1; continuous reinforcement) lever pressing was elicited by 2-mul but not by 1-mul procaine. The FR 64 pressing appeared to be disrupted during a period of increased activity following procaine injection, although visual observations indicated that the pressing which did occur was normal in topography and was significantly associated in temporal sequence with approaches of the food magazine.     

Effects of pre- or post-training paradoxical sleep deprivation on two animal models of learning and memory in mice

The aim of the present study was to verify the effects of pre- or post-training paradoxical sleep (PS) deprivation in mice tested in the passive and the plus-maze discriminative avoidance tasks. Three-month-old Swiss male mice were placed in narrow platforms in a water tank for 72 h to prevent the occurrence of PS. Control animals were kept in the same room, but in their home cages. Before or after this period, the animals were submitted to the training session of one of the behavioral tasks. The test sessions were performed 3 and 10 days after the training. The animals that were PS-deprived before the training session showed retention deficits in the test sessions performed 3 days later in both tasks (decreased latency to enter the dark chamber of the passive avoidance apparatus or increased percent time spent in the aversive arm of the plus-maze discriminative avoidance apparatus). Animals that were PS deprived after the training session showed no differences from control animals in the test sessions performed 3 days after the training in any of the tasks, but showed passive and discriminative avoidance retention deficits in the test performed 10 days after the training. The results suggest that both pre- and post-training paradoxical sleep deprivation produce memory deficits in mice. However, these effects have different temporal characteristics.     

Long-term spontaneous improvement of performance is related to the strength of the initial training: theoretical implications

In a recent study we established that following a partial acquisition of a brightness discrimination escape task (15 trials), Sprague-Dawley albino rats exhibited a long-term spontaneous improvement of performance (LTSI) after 7 to 14 days. Some evidence suggests a relation between the strength of the initial training and the delay of the optimal retention performance. This study investigates such a possibility in studying performance of rats (number of trials needed to reach a criterion of 10 errorless trials) following nine different retention intervals: 10 min, and 1, 3, 5, 7, 10, 14, 21, and 28 days, after a strengthened initial training (25 trials). Under those conditions, LTSI occurred after a delay of 5 to 7 days. Theoretical implications for an inverse relationship between the strength of initial training and the length of delay leading to LTSI are discussed.     

Development of place navigation in rats from weaning to puberty

Young hooded rats were trained to escape onto a hidden platform after swimming in a pool of opaque water. Subjects 21, 28, 35, 42, and 64 days of age on the first training day were given 28 trials on 5 consecutive days. Half of the rats were required to localize the platform in relation to external room cues only ("place only" condition) and the other half were helped by the presence of a visible cue on the platform ("cue + place" condition). A deficiency in place navigation was observed in the 21- and 28-day groups; they showed slow escape and took circuitous routes more often than older rats. This deficiency was related to a poor spatial bias toward the training position when the subjects were allowed to swim for 30 s in the absence of the platform, at the end of the 28-trial training period (probe trial). The 35-day group showed adult-like learning ability in both training conditions, but failed to show searching behavior during the probe trial after having been trained in the presence of the proximal cue. Only rats older than 40 days showed typical adult behavior such as swimming directly toward the platform from any starting position and localized searching around the absent platform's position during the probe trial, no matter what the training conditions were. These results suggest that central nervous system structures responsible for place learning in the rat are functional from around 32 days of age, but fail to trigger searching behavior following cued training before the sixth week.     

Learned helplessness in the rat.

Four experiments attempted to produce behavior in the rat parallel to the behavior characteristic of learned helplessness in the dog. When rats received escapable, inescapable, or no shock and were later tested in jump-up escape, both inescapable and no-shock controls failed to escape. When bar pressing, rather than jumping up, was used as the tested escape response, fixed ratio (FR) 3 was interfered with by inescapable shock, but not lesser ratios. With FR-3, the no-shock control escaped well. Interference with escape was shown to be a function of the inescapability of shock and not shock per se: Rats that were "put through" and learned a prior jump-up escape did not become passive, but their yoked, inescapable partners did. Rats, as well as dogs, fail to escape shock as a function of prior inescapability, exhibiting learned helplessness.     

Rats learn the relationship between responding and environmental events: An expansion of the learned helplessness hypothesis

Previous research has shown that preexposure to inescapable shock interferes with subsequent acquisition of escape responding, while pretraining with escapable shock facilitates subsequent acquisition of a different escape response. It has also been demonstrated that interference and facilitation persist when the aversive event is changed between the two phases of training. The present experiment extended these findings, showing generalized learning from an appetitive to an aversive situation. Six groups of rats received the following treatment in the presence of discriminative stimuli: One group was trained to nose press for food, a second to chain pull for food, and a third to chain pull to escape or avoid shock. Two groups received either signalled free food or inescapable shock, and a naive control group received no pretreatment. All groups were then tested in a nose-press escape-avoidance situation. The three groups with prior response training acquired responding most rapidly, and at the same rate. The naive controls acquired responding slowly, and the two groups with response-independent histories did not acquire responding during the 5 days of training. It was concluded that rats learn the relationship between responding and environmental events and that such learning strongly influences subsequent learning.     

The facilitative effects of intraseptal 6-hydroxydopamine injections on time discrimination behavior in rats

Twenty one male albino rats of the Wistar strain were trained on a differential reinforcement of long latency 20 with a limited hold 36 schedule through 30 consecutive days. Six rats were injected into the medial septal area with 8 micrograms of 6-hydroxydopamine dissolved in 0.9% saline solution containing 0.1% ascorbic acid. Five rats were injected with only ascorbic acid solution and the remaining rats were not treated with any injection or surgical operation. As a result of this differential reinforcement of long latency training, the 6-hydroxydopamine-injected rats showed significantly better performance and less acceleration of lever pressing response just after nonreinforced responses (incorrect responses) compared with the other two control groups, especially in the early 10 sessions. These findings suggested that the 6-hydroxydopamine-injected rats were hardly affected by response acceleration following nonreinforcements and therefore could acquire this training schedule faster than could the controls. The authors proposed one probable hypothesis, that the catecholaminergic input to the septum mediated a frustrated emotional response such as response acceleration resulting from nonreinforcements and impaired behavioral inhibition in the time discrimination situation.