Septal lesions facilitate the shift from conditioned escape to conditioned avoidance behavior in the rat.

Normal rats were given 1000 training trials in a discriminated lever-press avoidance task. Those animals which exhibited consistent escape behavior but minimal avoidance responding were subjected to either septal lesions or control operations. One week later they were retested in the avoidance apparatus for an additional 1000 trials. Rats with large septal lesions exhibited an immediate increase in avoidance performance relative to the control rats. This increase occurred without a concomitant increase in number of lever-press responses. The performance of 3 out of 4 rats with smaller more dorsal septal lesions was unaffected by the surgery.     

Disruption of maternal behavior in rats with lesions of the septal area

Rats given septal lesions prior to mating did not build nests or nurse their pups. During retrieving tests they carried pups about the cage repeatedly and dropped them in scattered locations. Virgin rats induced to be maternal by housing with foster pups showed similar, but less marked, behavioral deficits. Rats administered septal lesions after parturition became hyperresponsive, ceased all maternal behaviors, and cannibalized their pups. The results indicated that the aberrant maternal behaviors shown by rats with septal lesions did not result from alterations in hormonal status. It was concluded that the lesions disrupted the typical pattern or sequence of maternal activities and that the deficits were probably related to an enhancement of response perseveration.     

Effect of bilateral septal lesions on discrimination avoidance conditioning in rats

Studies were performed, using the two-way shuttle box method, on the acquisition of discrimination avoidance by rats with bilateral lesions of the septum (septal rats) in relation to changes in emotional behavior. Septal rats exhibited hyperreactivity immediately after the lesions were made: their startle, struggle and vocalization responses to stimuli were markedly increased. These hyperemotional responses, however, decreased and returned to the normal level 7 days after surgery. Initially, the septal rats showed elevated conditioned avoidance responses to both the CS+ and the CS-. In later stages, their responses to the CS+ showed progressive and gradual increase, accompanied by a decrease in responses to the CS-, until responses to both stimuli were only slightly elevated above the level of control rats. These results suggest that bilateral lesions of the septum do not affect discrimination ability itself. The impairment of discrimination avoidance during the initial stages may result from the transient impairment of the discrimination acquisition process.     

Comparison of the effects of frontal, striatal, and septal lesions in paradigms thought to measure incentive motivation or behavioral inhibition

Bilateral electrolytic lesions of the ventral, but not dorsal, anterior striatum produced over-responding in rats performing on a modified DRL-30 sec schedule of reinforcement. This effect appears similar to that previously seen in rats with septal lesions but an analysis of the types of errors indicated important differences between the effects of septal and striatal lesions. Comparisons of rats with frontal, striatal and septal lesions with respect to their acquisition of saccharine licking, latency to eat in a novel environment, and acquisition of a runway response indicated that only septal lesions reliably enhance approach tendencies in these tests. The data suggest that the behavioral changes seen after striatal or frontal damage in the rat are not due to enhanced responsivity to rewarding stimuli.     

Excitotoxic lesions to the prefrontal cortex of Sprague–Dawley rats do not impair response matching

Perseveration refers to maladaptive persistence of behavior outside appropriate contexts and despite negative outcomes. In humans, perseveration is a symptom of a variety of psychiatric disorders. In rats, perseveration has been observed in reversal learning tasks following lesions of the prefrontal cortex (PFC). However, the exact nature of the impairment underlying this effect remains unclear. Male Sprague–Dawley rats were trained on a novel reversal task that requires switching between two rewarded options varying in effort (concurrent fixed and progressive ratios) necessary to obtain the reward. Following initial training, bilateral lesions of the dorsal PFC, medial PFC, or orbitofrontal cortex were produced by NMDA infusions. When animals were re-tested post-surgery, no significant impairments were found. These results indicate that, in trained rats, the PFC is not necessary for selecting responses on the basis of favorable effort-to-reward contingencies.     

Failure to reactivate the septal syndrome in rats

Electrolytic lesions in the septal region of albino rats produced the expected septal hyper-reactivity syndrome. Following abatement of the syndrome with daily handling, attempts were made to restore the hyper-reactivity with three techniques: abrupt reward decrement in an instrumental responding situation (frustration); exposure to both moderate and intense electric foot shock; and exposure to intense startle-eliciting tonal bursts. The treatments failed to elevate reactivity of the rats with septal lesions above control levels. Data from the instrumental responding situation provided support for the hypothesis of enhanced incentive properties of rewarding stimuli by septal lesions.     

Effects of lateral and medial septal lesions on various activity and reactivity measures in rats

Roles of the lateral and medial septum in the regulation of activity, reactivity and open field behavior in rats were examined in the present study. Effects of lateral, medial and combined lateral and medial septal lesions were studied, respectively. Our results indicate that lateral septal lesions significantly decreased locomotor activity and tended to decrease rearing response. While it also markedly increased movement time in the activity monitor, stereotyped behavior and tactile startle amplitude. The most significant findings with medial septal lesions were decreased activity, especially in the center area of an open field and decreased exploratory behavior in rats. For most behavioral measures, effects of combined lateral and medial septal lesions were similar to that of medial septal lesions alone except that it augmented startle response with a different response pattern compared to that of lateral septal lesions alone. The locomotion patterns of these animals also revealed some qualitative difference in their behavior. These results are further discussed in the scope of anatomical, neurochemical and pharmacological differentiations of the septum complex.     

Activity changes during a conditioned aversive stimulus in rats with septal lesions.

The effect of a stimulus previously associated with shock on the spontaneous activity of rats with septal lesions and operated control rats was determined. All rats first received 50 signaled inescapable shock trials and then the signal was presented during a spontaneous activity task. Presentation of the signal during the activity task resulted in an exaggerated increase in activity in rats with septal lesions whereas control rats displayed only a slight increase in activity alternated with periods of no activity. The results are consistent with a reduced freezing hypothesis of septal lesions in aversive learning situations.     

Effects of dorsomedial thalamic lesions on spatial discrimination reversal in the rat.

Eight rats with lesions of the dorsomedial thalamus and 10 rats with sham operations were compared on acquisition and subsequent reversals of a spatial discrimination. The rats with thalamic damage showed greater perseveration to the incorrect choices (p less than 0.002) and made fewer reversals (p less than 0.05) and more errors (p less than 0.02) during the 100 reversal trials following initial acquisition than did the sham-operated animals. The two groups did not differ on the original acquisition.     

A water-maze discrimination learning deficit in the rat following lesion of the habenula

Although the habenula occupies a potentially important link between forebrain and midbrain, lesion of the complex produces little effect in most standard behavioral paradigms. More recently, it has been shown that such lesions may impair the ability to initiate or switch responses appropriate to environmental contingencies but only under demanding conditions. Although such deficits have been described as response failures, they could equally well be attributed to restricted attentional mechanisms. The present study was designed to further substantiate a role for the habenula in acquisition of adaptive behavior under demanding conditions and to examine the possible contribution of attentional failure. The initial response preference to 'escape' onto platforms situated in two chambers at the distal end of a water tank was established for groups of lesioned and sham-operated rats. Rats were subsequently trained in discrete trials to escape by choosing the side of the nonpreferred chamber. During training the choice of escape chamber was cued by distracting black or white visual stimuli displayed on the tank sides and above the entrances to the chamber. These were moved over trials so as to be nonpredictive of the appropriate escape position. Lesioned animals were significantly impaired in the acquisition of this positional discrimination. Analysis of response times suggested that both lesion and control animals were attending to the irrelevant visual cue. The results confirm a behavioral inflexibility following lesion of the habenula and suggest that this deficit cannot be explained simply in terms of a failure to attend to environmental cues. The lesion deficit also could not be attributed to a response perseveration.     

Septal lesions,intramaze cues and spatial behavior in rats

In agreement with previous findings septal lesions profoundly disrupted performance of a preoperatively established spatial habit in an 8 arm radial maze. The addition of intramaze cues that served to make each arm distinct did not improve performance of the subjects with septal lesions. The few animals with septal lesions that reacquired proficient performance apparently did so by adopting and adhering to response strategies. Derangement of complex spatial behavior following septal lesions appears to involve an inability to use spatial information rather than a shift in behavioral control from interoceptive response-produced cues to exteroceptive stimuli.     

Effects of septal lesions on the behavior of amygdalectomized rats towards mice (author's transl)]

In spontaneously nonkilling rats, septal lesions induce the initiation of mouse-killing behavior whenever a prior lesion of the medial part of the amygdala was performed 3 months earlier. The lesion elicits the characteristic septal hyperreactivity, as the animals have recovered from the opposite effect of the amygdaloid lesion after that prolonged delay. The initiation of interspecific aggressive behavior by septal lesions in intact nonamygdalectomized rats depends on the degree of preoperative familiarity with the mouse. As a matter of fact, septal lesions induce by themselves very few aggressive reactions in previously nonkilling rats. The amygdaloid lesion abolishes the capacity to develop a stable inhibition of the killing behavior on the basis of repeated contacts with a mouse. These results confirm that the amygdala is involved in the development and maintenance of a specific behavioural inhibition in the nonkilling rat.     

Effects of septal lesions on the discrimination of fixed-ratio performance

Rats with septal lesions and control rats were required to press the center lever of a three lever operant chamber a fixed number of times before activating the side levers. If the rat pressed the center lever 32 times, then a response on the right lever was correct and food was delivered. If the rat pressed 2, 4, 8, or 16 times on the center lever, then a response on the left lever was correct. Both groups were able to discriminate between long and short fixed-ratio schedules. As expected, more errors were made as the discrimination became more difficult. Septal rats, however, were unable to discriminate as well as control rats. These data suggest that septal lesions interfere with rats' ability to monitor response-produced proprioceptive stimuli.     

Attenuation of reversal deficits of mice with septal lesions by shifts in the motivational context

Response perseveration following septal lesions, demonstrated on tasks that require change of a learned pattern of responding, depends in part on a relatively constant motivational context. The present experiment examined the effects of concurrent changes in the temperature of the water in a water-escape maze and the reversal of a spatial discrimination in mice that had received either septal lesions or control surgery. Control and experimental mice were trained on a spatial discrimination in either 17 or 34 degrees C water. Following acquisition, reversal training was conducted in the maze filled with the same-temperature water used during acquisition or water temperature as well as spatial reinforcement contingencies were reversed. When the water temperature remained constant across acquisition and reversal, the mice with septal lesions showed persistence during reversal training. Changing the water temperature concurrently with the institution of reversal training attenuated the perseverative deficits of mice with lesions, in contrast to the relative lack of effect in control animals. These results are discussed within the framework of the role that the septal region plays in attention.     

Interaction between the septal area and the subfornical organ in the control of water intake induced by thirst-eliciting procedures

Rats bearing lesions in the septal area followed by lesions in the subfornical organ were submitted to various thirst-eliciting procedures. The rats with hyperdipsia induced by lesions of the septal area drank more water than either during the control period or after lesion of the subfornical organ under the same thirst-eliciting or angiotensin-liberating stimuli (polyethyleneglycol, isoproterenol, water deprivation and ligation of the inferior vena cava). The overdrinking elicited by lesions in the septal area was blocked after lesion of the subfornical organ. Neither hypovolemia, nor hypotension or water deprivation could elicit increased water intake in animals whose subfornical organ had been destroyed. Animals with lesions in the subfornical organ showed decreased water intake after cellular dehydration. The results obtained suggest that the subfornical organ acts as a more important structure than the septal area in the regulation of water intake elicited by angiotensin, with two opposite effects: a direct one facilitating water intake, and an indirect one inhibiting the septal area. The septal area has an inhibitory effect on the subfornical organ and on water intake.     

Differential effects of septal lesions on attack and defensive-submissive reactions during intraspecies aggression in rats

The effects of septal lesions on attack, threat, defense and submission were studied in rats without prior fighting experience (Experiment 1) and in rats that were either dominant or subordinate in preoperative aggressive encounters (Experiment 2). A factor analysis showed that the various components of agonistic behavior could be grouped into three factors characterizing attack/submission (Factor 1), threat/defense (Factor 2), grooming and crouching (Factor 3). Septal lesions impaired attack, threat, grooming and crouching in experienced dominant or socially naive animals in encounters with unoperated opponents. But septal lesions in experienced subordinate animals failed to alter significantly submissive-defensive reactions. Surprisingly, the immobile-crouch reaction, predominantly displayed by a subordinate rat in the presence of a dominant rat, remained unchanged after septal lesions. These results suggest that septal lesions affect only specific components of the rat's attack and defense behavior. Several current theories on the behavioral functions of the septum, emphasizing response inhibition, fear reduction, and species-specific dispositions, can only partly accommodate these results.     

Open-field social behavior of rats following lateral or medial septal lesions

Long-Evans hooded rats were selected at random and assigned to one of six groups. Animals in each group were rated on an emotionality scale and observed in pairs on 10 successive preoperative days and 14 successive postoperative days in an open field. Total number of contacts, length of contact time, and number of aggressive or submissive behaviors which occurred in a 15 min observation period were recorded daily. Following surgery animals with lateral septal lesions displayed hyperemotionality which decreased after handling. The emotionality of the animals with medial septal or cingulate cortex lesions did not change postoperatively. Medial septal lesions resulted in a postoperative increase in contact time, a decrease in number of discrete contacts, and a higher frequency of submissive behaviors. Lateral septal lesions had little effect upon contact time or number of contacts but increased aggressive encounters slightly. Cingulate cortex lesions did not affect open-field social behavior. Changes observed in social behavior were related to changes in both an animal's tendency to emit behaviors and its tendency to react to behavior emitted by its partner.     

Septal lesions increase play fighting in juvenile rats

Play fighting is a behavior exhibited by juveniles of many mammalian species, but the neurology of this behavior is poorly understood. In the present study lesions of the septal area or control operations were performed in rats at 23 days of age and social play was studied between the ages of 27–41 days of age. Septal lesions increased the frequency of play fighting and play initiation in both sexes; within the lesion and control groups males played more frequently and initiated more play bouts than females. Animals with septal lesions were somewhat lighter in body weight than controls, but since play frequency and body weight were not associated, it is unlikely that changes in body weight caused by the lesions are responsible for the effects of the lesions on play.     

Nutritional experience and spacing of shock opportunities alter the effects of septal lesions on passive avoidance acquisition by male rats

Male rats which had received septal lesions or control operations were maintained on a 23 $\text{1}\text{2}$ hour water deprivation schedule. They were tested on the acquisition of a water passive avoidance task under either of two schedules of shock availability. When septal rats were limited to one shock per daily session they did not require more shocks than controls in meeting the acquisition criterion (2 consecutive days without initiating shock). Regardless of shock schedule, rats with septal lesions met the acquisition criterion in the same number of days as controls. A presurgical history of dietary sodium depletion was also found to differentially affect the behavior of septal and control rats under the multiple-shock schedule. These results further indicate the importance of both experiential and situational variables in determining the behavioral effects of septal lesions.     

Discrimination behavior of rats with septal lesions in a cue addition deletion paradigm.

The discrimination behavior of rats with septal lesions is affected by their altered reactivity to stimulus conditions surrounding the learning situation. Compared to control animals rats with septal lesions are differentially affected by experience with cues relevant to the task itself. In the present experiment we examined the effects of septal lesions on how the rat responds to, and subsequently utilizes, cue information which is made relevant after the animal had achieved criterion performance in a discrimination task. Relative to control animals, rats with septal lesions apparently failed to attend to the newly relevant cues provided, and clearly were deficient when later called upon to utilize such information. However, the degree of deficit was related to the difficulty exhibited in acquisition of original learning. Thus, the more difficult the original learning task, the less deficient were lesioned animals compared to their control counterparts in subsequent situations demanding the utilization of new information. These findings are consistent with our notion that septal lesions alter the relative weighting placed on specific information which the CNS must process. Changes in learning performance reflect altered sensory reactivity.