The GM1 ganglioside hastens the reduction of hyperemotionality after septal lesions

The purpose of the present study was to assess the effects of ganglioside treatment on changes in emotional, activity, and avoidance behaviors following septal brain damage. Rats were treated with GM1-gangliosides either before and after septal lesions, or only after septal lesions and tested for emotionality on 10 consecutive days beginning on the second day after surgery. The ganglioside treatment decreased the emotionality of rats with septal damage on the first test day, and enhanced their rate of recovery to control levels of emotionality. Septal rats treated with gangliosides had activity, rearing, and avoidance behaviors equivalent to nontreated septal rats; however, lesioned rats treated with GM1 showed reduced intertrial crossings during avoidance conditioning. These results suggest that the changes in emotional behavior of septal rats treated with GM1 occur shortly after the lesion.     

Performance of rats on the Maier three-table task following septal lesions occurring 24 hours after birth

The purpose of this study was to determine whether behavioral sparing would be demonstrated when septal lesions occurred prior to the age at which the tested behavior first appears in normal rats. Rats given septal lesions at 1 day or 7 days after birth performed at approximately chance on the Maier three-table task when tested at 90 days of age. Rats that had control electrode insertions at the same ages performed at a level similar to normal animals. Animals given septal lesions at either age explored significantly more than did control animals. Results are discussed in terms of the constancy over time of the septal contribution to performance on the three-table task and the involvement of the septum and hippocampus in the processing of spatial information.     

The long-term effect of high- and low-rate responding histories on fixed-interval responding in rats

Tell rats were given extended lever-press training on a fixed-interval (FI) 30-s food reinforcement schedule from the outset or following exposure to one or two previous reinforcement schedules. For 4 rats the previots schedule was either fixed-ratio 20, which generated high response rates, or differential-reinforcement-of-low-rate 20 s, which produced low response rates. For 4 additional rats the extended training on FI 30 s was preceded by experience with two schedules: fixed-ratio 20 followed by differential-reinforcement-of-low-rate 20 s; or the same two schedules in the reverse order. Fixed-interval response rates were initially affected by the immediately preceding schedule, but after 80 to 100 sessions, all traces of prior schedule history had disappeared. The results also showed no long-term effect of schedule history on the interfood-interval patterns of responding on the FI 30-s schedule. These results support one of the most central tenets of the experimental analysis of behavior: control by the immediate consequences of behavior.     

Nimodipine accelerates recovery from the hyperemotionality produced by septal lesions

Rats with large electrolytic lesions of the septal area were given the calcium channel antagonist nimodipine (70 micrograms/kg, ip) or its vehicle on the day of surgery and for 3 subsequent days. They were tested for emotionality and compared to control rats for 10 days beginning on the third day after surgery. Forty days after surgery all animals were trained in a two-way active avoidance task for 120 trials. Nimodipine reduced the hyperemotionality found after septal lesions as early as the first test day, and increased the rate of recovery toward control levels on subsequent days. Both septal-lesion groups exhibited more avoidance responses than controls, even though the intertrial crossings were enhanced only in rats with septal lesions that did not receive nimodipine.     

Paleostriatal lesions and instrumental learning in the pigeon

In three experiments, pigeons with lesions of the paleostriatum (experimental subjects) and unoperated control birds were trained on tasks designed to assess their instrumental learning abilities. In Experiment 1, using an orthodox Skinner box, training was given on a variable interval (VI) followed by a fixed interval (FI) schedule of reinforcement and only non-significant differences between the groups emerged. Experiment 2 examined the performance of the same subjects on a VI schedule in which a response-contingent signal accompanied reinforcement. For control subjects the presence of the signal resulted in a low rate of response compared with that found in equivalent conditions with the signal omitted. Experimental subjects showed the same response rate when the signal was present as when it was absent. Experiment 3 employed naive subjects, and a Skinner box modified to facilitate key-pecking in total darkness. In this apparatus, experimental subjects showed a lowered response rate on a VI schedule. These tasks were analyzed in terms of the classical (stimulus-reinforcer) and instrumental (response-reinforcer) learning they involve. The results suggest that pigeons with paleostriatal lesions show a deficit in forming response-reinforcer associations, perhaps because the lesions reduce the salience of response-produced cues.     

Competitive fixed-interval performance in humans

Two persons responded in the same session in separate cubicles, but under a single schedule of reinforcement. Each time reinforcement was programmed, only the first response to occur, that is, the response of only one of the subjects, was reinforced. “Competitive” behavior that developed under these conditions was examined in three experiments. In Experiment 1 subjects responded under fixed-interval (FI) 30-s, 60-s, and 90-s schedules of reinforcement. Under the competition condition, relative to baseline conditions, the response rates were higher and the pattern was “break-and-run.” In Experiment 2, subjects were exposed first to a conventional FI schedule and then to an FI competition schedule. Next, they were trained to respond under either a differential-reinforcement-of-low-rate (DRL) or fixed-ratio (FR) schedule, and finally, the initial FI competition condition was reinstated. In this second exposure to the FI competition procedure, DRL subjects responded at lower rates than were emitted during the initial exposure to that condition and FR subjects responded at higher rates. For all subjects, however, responding gradually returned to the break-and-run pattern that had occurred during the first FI competition condition. Experiment 3 assessed potential variables contributing to the effects of the competitive FI contingencies during Experiments 1 and 2. Subjects were exposed to FI schedules where (a) probability of reinforcement at completion of each fixed interval was varied, or (b) a limited hold was in effect for reinforcement. Only under the limited hold was responding similar to that observed in previous experiments.     

Visual sampling after lesions of the superior colliculus in rats

In two separate experiments, rats with bilateral lesions of the superior colliculus showed significantly poorer relearning of a horizontal/vertical stripe discrimination than control animals. In Experiment 1, all animals showed disruption of performance when a stimulus--response (S--R) separation was introduced by raising the stimuli above the site of responding. However, the colliculectomized rats were much more disturbed by the S--R separation than were animals in the control group. In Experiment 2, all animals showed lower performance levels when conflicting patterns were introduced into the upper portion of the stimulus doors, but this time the rats with collicular lesions were less disturbed than the control animals. It is suggested (a) that when the stimulus and response sites are discontiguous, animals must make an appropriate orienting response in order to effectively sample the visual stimuli and (b) that lesions of the superior colliculus alter performance by interfering with this orienting behavior. The impairment in relearning is tentatively attributed to the absence of preoperative overtraining on the discrimination task.     

Active avoidance behavior following archistriatal lesions in pigeons.

Experiment 1 examined the performance of 10 pigeons, 5 with bilateral medial archistriatal lesions and 5 sham-operated controls, in the acquisition and maintnenance of a discrete-press avoidance response. The archistriatal subjects had longer response latencies and never attained the level of performance achieved by the controls. In Experiment 2 eight pigeons learned a treadle-press response to avoid or escape shock on a signaled free-operant schedule. After 17 daily sessions four subjects received bilateral lesions in the medial archistriatum, and four received control lesions in the neostriatum. After recovery from surgery, all subjects were returned to the experimental procedure. Avoidance of those subjects with archistriatal lesions was impaired relative to the postoperative level while that of the control group was unchanged. These results are interpreted in the light of earlier experiments showing reduced escape and avoidance behavior both in order avian species and in mammals with lesions in the amygdala, to which the archistriatum is considered homologous.     

Hormonal dissociation of limbic lesion effects on shuttle box avoidance in rats.

Rats with septal or hippocampal lesions, relative to normal rats, showed facilitated acquisition of a shuttle box avoidance response. The rats with septal lesions were also highly resistant to extinction compared with normal rats. When the same lesion effects were examined in hypophysectiomized rats, the animals with septal lesions continued to show facilitated performance, and those rats with hippocampal lesions performed no differently than nonoperated control animals. These findings are consistent with the hypothesis that the facilitated avoidance performance found in rats with hippocampal lesions is attributable to lesion-induced changes in hypophyseal activity, but similar changes induced by septal lesions are not.     

Perirhinal cortex lesions impair feature-negative discrimination

The role of the perirhinal cortex in inhibitory eyeblink conditioning was examined. In Experiment 1, rats were given lesions of the perirhinal cortex or control surgery and subsequently trained with a feature-negative discrimination procedure followed by summation and retardation tests for conditioned inhibition. Perirhinal cortex lesions impaired, but did not prevent acquisition of feature-negative discrimination. Results from the summation test showed that rats with perirhinal cortex lesions could not generalize feature-negative discrimination to a new stimulus. There were no group differences during the retardation test. Experiment 2 showed that lesions of the perirhinal cortex did not impair simple excitatory conditioning. Experiment 3 showed that perirhinal cortex lesions had no effect on acquisition of a simple tone-light discrimination. The results suggest that the perirhinal cortex plays a role in eyeblink conditioning when using discrimination procedures involving overlapping stimuli.     

The effect of signaled reinforcement on rats' fixed-interval responding

Four experiments examined the effect on rats' response rate of presenting a brief (500 ms) stimulus simultaneously with the delivery of food on fixed-interval (FI) schedules. In Experiment 1, reinforcement signals that were spatially diffuse (both tones and lights) elevated rates of responding, but responding was attenuated by localized visual stimuli. The remaining experiments examined the signal-induced potentiation of responding. In Experiment 2, a tone reinforcement signal potentiated response rates on an FI schedule, but attenuated response rates on a variable-interval (VI) schedule. This difference was obtained even though the overall rate of responding was equated on the two schedules before the introduction of the signal. Signal-induced potentiation of responding occurred over a range of FI values employed in Experiment 3. In Experiment 4, presenting a reinforcement signal when high local rates of response had occurred immediately before reinforcement resulted in potentiated rates of responding on an FI schedule. The opposite effect on response rate occurred when the reinforcement signal followed only low local rates of response. These results indicate that a variety of factors influence the effects of a reinforcement signal. They imply, however, that the local rate of response at the time of reinforcement is a key factor in establishing the nature of the signaling effect.     

Suppressive and enhancing effects of footshock on food-reinforced operant responding following septal lesions in rats.

Effect of septal lesions on suppression of an intermittently food-reinforced lever press by contingent and noncontingent footshock was measured. Rats with septal damage maintained higher response rates than did intact animals under both contingent and noncontingent shock. Furthermore, the difference in suppression produced by the contingent and noncontingent conditions was approximately the same for the experimental and control groups. In a second experiment, performance was measured during counter-conditioning in which the correlation between contingent shock and positive reinforcement was varied. Rats with septal lesions responded at higher rates than did controls. When only reinforced responses were punished, this lesion-induced elevation represented an increase above baseline performance without punishment. This finding suggests that the effect of septal damage on appetitive instrumental performance cannot be due solely to a deficit in response inhibition.     

Revisiting places passed: sensitization of exploratory activity in rats with hippocampal lesions

We examined the involvement of the hippocampus in short-term changes in exploratory behaviour in an open field (Experiment 1) and experimental contexts (Experiment 2). In Experiment 1, rats with excitotoxic lesions of the hippocampus were more likely to revisit recently visited zones within the open field than were control rats. Similarly, in Experiment 2 rats with hippocampal lesions showed greater exploration of a context that they had recently explored than a context that they had less recently explored. This short-term sensitization effect was not evident in control rats. These findings are consistent with the suggestion that the recent presentation of a stimulus has two opposing effects on behaviour, sensitization, and habituation, and that hippocampal lesions disrupt the short-term process responsible for habituation, but not that responsible for sensitization.     

Revisiting places passed: Sensitization of exploratory activity in rats with hippocampal lesions

We examined the involvement of the hippocampus in short-term changes in exploratory behaviour in an open field (Experiment 1) and experimental contexts (Experiment 2). In Experiment 1, rats with excitotoxic lesions of the hippocampus were more likely to revisit recently visited zones within the open field than were control rats. Similarly, in Experiment 2 rats with hippocampal lesions showed greater exploration of a context that they had recently explored than a context that they had less recently explored. This short-term sensitization effect was not evident in control rats. These findings are consistent with the suggestion that the recent presentation of a stimulus has two opposing effects on behaviour, sensitization, and habituation, and that hippocampal lesions disrupt the short-term process responsible for habituation, but not that responsible for sensitization.     

Resurgence and repeated within-session progressive-interval thinning of alternative reinforcement

Resurgence of a previously suppressed target behavior is common when reinforcement for a more recently reinforced alternative behavior is thinned. To better characterize such resurgence, these experiments examined repeated within-session alternative reinforcement thinning using a progressive-interval (PI) schedule with rats. In Experiment 1, a transition from a high rate of alternative reinforcement to a within-session PI schedule generated robust resurgence, but subsequent complete removal of alternative reinforcement produced no additional resurgence. Experiment 2 replicated these findings and showed similar effects with a fixed-interval (FI) schedule arranging similarly reduced session-wide rates of alternative reinforcement. Thus, the lack of additional resurgence following repeated exposure to the PI schedule was likely due to the low overall obtained rate of alternative reinforcement provided by the PI schedule, rather than to exposure to within-session reinforcement thinning per se. In both experiments, target responding increased at some point in the session during schedule thinning and continued across the rest of the session. Rats exposed to a PI schedule showed resurgence later in the session and after more cumulative alternative reinforcers than those exposed to an FI schedule. The results suggest the potential importance of further exploring how timing and change-detection mechanisms might be involved in resurgence.     

Caudate-putamen lesions in the rat may impair or potentiate maze learning depending upon availability of stimulus cues and relevance of response cues

In Experiment 1 rats were required to learn a Y-maze in which reward was made available after a given response (e.g. a left turn) regardless of which arm was used as the start-box. Subjects with lesions of the caudate-putamen showed a deficit on this response-learning task compared with control subjects (unoperated animals and rats having lesions of the posterior cortex). In Experiment 2 rats with caudate-putamen lesions were unimpaired when the direction of the turn required to reach the correct goal-box (identified by means of a salient visual intra-maze cue) varied from trial to trial. In the absence of salient intramaze cues, but with enriched room (extra-maze) cues, the rats with caudate-putamen lesions were superior to controls on this task. It is argued that caudate-putamen lesions disrupt a mechanism responsible for processing information about responses, but that the other (spatial) mechanisms responsible for maze-learning remain intact and that caudate-putamen lesions may enhance performance on spatial tasks for which information about responses is irrelevant.     

Septal lesions lower responding under fixed-ratio schedules of reinforcement.

Albino Sprague-Dawley rats with complete septal lesions and rats with control operations were studied under fixed-ratio (FR) schedules of reinforcement. Both groups were trained for 10 sessions each under FR 10, 20, 40, 60, 80, and 100. In contrast to findings from progressive FR studies and some simple FR studies, septal lesions resulted in lower overall and local response rates along with longer postreinforcement pauses. These effects were especially evident during the FR 100 schedule of reinforcement. A comparison of reinforcement rate as a function of FR size within the context of behavioral economics (i.e., a demand function) indicated that septal lesions did not alter the reward value of food. These findings suggest that responding on FR schedules of reinforcement can be altered by the various procedures used to train rats to reach the terminal value of a reinforcement schedule.     

A limited role for the hippocampus in the modulation of novel-object preference by contextual cues

Recent evidence suggests that rats require an intact hippocampus in order to recognize familiar objects when they encounter them again in a different context. The two experiments reported here further examined how changes in context affect rats' performance on the novel-object preference (NOP) test of object-recognition memory, and how those effects interact with the effects of HPC damage. Rats with HPC lesions and control rats received NOP testing in either the same context in which they had previously encountered sample objects, or in a different but equally familiar context. In Experiment 1, the two contexts had very few overlapping cues within or outside the apparatus; thus, the differences between them were global. Consistent with previous results, control rats showed a novel-object preference in both the unchanged and (globally) changed contexts, whereas rats with HPC lesions displayed a preference only in the unchanged context. In Experiment 2, the context shift included only local features proximal to the test objects. The main results were the reverse of Experiment 1--rats with HPC lesions displayed a novel-object preference in both the unchanged and (locally) changed contexts, whereas control rats displayed a preference only in the unchanged context. The findings are consistent with the view that HPC damage does not cause a general inability to recognize objects, nor an inability to encode or store a representation of the context in which the objects are encountered. They suggest instead that HPC damage impairs the ability to remember specific locations of familiar objects within a particular context.     

The effects of lateral, medial, or complete septal lesions on positive conditioned suppression in rats

This study investigated the effects of lateral, medial, or complete septal lesions in rats on lever pressing and US-approach behaviors during the presentation of a light followed by two free food pellets. Ten days after surgery, groups of rats received 20 sessions of a random interval (RI) 60-s schedule of food reinforcement. The positive conditioned suppression paradigm consisted of 20 sessions of a 10-s light paired with free food while the rats were responding on the RI 60-s schedule. All groups of rats significantly suppressed lever pressing during the 10-s light presentation. During the last four sessions of the 10-s light condition, rats with lateral septal lesions had a significant increase in food-tray entries during the light presentation, while the other groups decreased lever pressing without a change in food-tray entries during the 10-s light presentation. Although rats with septal damage generally have difficulty inhibiting responses in a variety of operant situations, rats with lateral, medial, or complete septal lesions showed no impairment in positive conditioned suppression. This study also suggests that when the spatial arrangement of the CS and the type of US were manipulated to minimize sign-tracking and goal-tracking behaviors, emotional reactions during the presentation of the CS must be considered a factor influencing positive conditioned suppression.     

Involvement of the rat anterior cingulate cortex in control of instrumental responses guided by reward expectancy

The anterior cingulate cortex (ACC) plays a critical role in stimulus-reinforcement learning and reward-guided selection of actions. Here we conducted a series of experiments to further elucidate the role of the ACC in instrumental behavior involving effort-based decision-making and instrumental learning guided by reward-predictive stimuli. In Experiment 1, rats were trained on a cost-benefit T-maze task in which they could either choose to climb a barrier to obtain a high reward (four pellets) in one arm or a low reward (two pellets) in the other with no barrier present. In line with previous studies, our data reveal that rats with quinolinic acid lesions of the ACC selected the response involving less work and smaller reward. Experiment 2 demonstrates that breaking points of instrumental performance under a progressive ratio schedule were similar in sham-lesioned and ACC-lesioned rats. Thus, lesions of the ACC did not interfere with the effort a rat is willing to expend to obtain a specific reward in this test. In a subsequent task, we examined effort-based decision-making in a lever-press task where rats had the choice between pressing a lever to receive preferred food pellets under a progressive ratio schedule, or free feeding on a less preferred food, i.e. lab chow. Results show that sham- and ACC-lesioned animals had similar breaking points and ingested comparable amounts of less-preferred food. Together, the results of Experiment 1 and 2 suggest that the ACC plays a role in evaluating how much effort to expend for reward; however, the ACC is not necessary in all situations requiring an assessment of costs and benefits. In Experiment 3 we investigated learning and reversal learning of instrumental responses guided by reward predictive stimuli. A reaction time (RT) task demanding conditioned lever release was used in which the upcoming reward magnitude (five vs. one food pellet) was signalled in advance by discriminative visual stimuli. Results revealed that rats with ACC lesions were able to discriminate reward magnitude-predictive stimuli and to adapt instrumental behavior to reversed stimulus-reward magnitude contingencies. Thus, in a simple discrimination task as used here, the ACC appears not to be required to discriminate reward magnitude-predictive stimuli and to use the learned significance of the stimuli to guide instrumental behavior.