Septal lesions enhance delay of responding on a free operant avoidance schedule

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The performance of rats with ventromedial hypothalamic (VMH) or septal lesions was compared with that of normal subjects on a discrete trial DRL task. Animals were pretrained at 85% of their ad-lib body weights and postoperatively tested at this level of deprivation and at greater and lesser deprivation levels. Septal rats emitted significantly more nonreinforced responses and had shorter response latencies than did control and VMH rats while tested at the different deprivation levels. VMH lesioned rats performed as well as controls_ Septal performance was not affected by deprivation level. Both VMH and control subjects obtained the greatest number of reinforcements while tested at the greater deprivation level. In spite of the large number of similarities between VMH and septal rats, VMH rats, unlike septal rats, used internal cues as well as normal rats did to perform proficiently on this task.Rats with lesions of the ventromedial hypothalamus (VMH) and septum display a number of behavioral similarities. Such animals are hyperreactive to touch (Singh, 1969), overresponsive to oro sensory characteristics of food (Beatty & Schwartzbaum, 1967;Corbit & Stellar, 1964;Singh & Meyer, 1968), and possibly hyperphagic (Singh & Meyer, 1968). Both septal and VMH rats display reduced spontaneous alternation activity in aT-maze (Singh, 1973a), decreased spontaneous behavior (Schwartzbaum & Gay, 1966;Teitelbaum, 1961), and poor performance on passive avoidance tasks (Hamilton, Kelsey, & Grossman, 1970;Margules & Stein, 1969; Singh, 1973a). Furthermore, Kaada (1951) observed that electrical stimulation of either the septum or VMH depressed respiration and blood pressure and would inhibit spinal reflexes and movement elicited by cortical stimulation.The behavioral similarities observed following septal and VMH lesions or stimulation suggest that these two areas are part of an inhibitory somatomotor system (Kaada, 1951(Kaada, , 1960. Van Hoesen, MacDougall, Wilson, and Mitchell (1971) have shown that septal rats perform poorly on a discrete trial DRL task (DT-DRL). During this task, the insertion of the lever into the operant chamber signals the start of the delay on DRL. The poor septal performance on this task was interpreted to indicate that septals are unable to organize collateral behaviors to bridge the delay period or to use response-produced cues.This research was supported in part by NIH Biomedical Research Support Grant RR07036. Requests for reprints should be addressed to James C. Mitchell, Department of Psychology, Kansas State University, Manhattan, Kansas 66506.In light of Kaada's hypothesis and the behavioral similarities of VMH and septal rats, it was of interest to see ifVMH rats also perform similarly on a DT-DRL task.Our initial observations showed no differences in performance between normal and VMH subjects, while septals performed less proficiently. In order to increase the likelihood of VMH-normal performance differences on this task, levels of food deprivation were subsequently manipulated. METHOD Subj...

Section: Discussionmentioning

confidence: 99%

Comparison of septal and ventromedial hypothalamic lesion effects on discrete trial DRL behavior

Flynn

Mitchell

1980

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“…As a decrement in shock intensity reduces the response output and increases the shock rate for normal animals (powell, 1970;Riess, 1970;Riess & Ferrar, 1972), it is difficult to reconcile these effects with fear reduction. An explanation in terms of response disinhibition fares no better as the increased efficiency of the brain-damaged rats appears to be at least partially due to the fact that they can space their responses more appropriately (Morgan & Mitchell, 1969;Sodetz, 1970Sodetz, , 1972. More detailed study of the patterns of responding on free-operant avoidance tasks following septal lesions seems necessary .…”

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confidence: 99%

“…A second purpose of the experiment was to make a detailed study of free-operant avoidance behavior following septal damage. Septal lesions in rats have been found to decrease both response (Morgan & Mitchell, 1969;Sodetz, 1970Sodetz, , 1972 and shock rates (Morgan & Mitchell, 1969;Sodetz, 1970;Duncan & Duncan, 1971) on leverpress free-operant avoidance. This increased effiCiency presents difficulties for both hypotheses under consideration.…”

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confidence: 99%

“…There is a decrement in both the shock (Duncan & Duncan, 1971;Morgan & Mitchell, 1969;Sodetz, 1970) and response rates (Morgan & Mitchell, 1969;Sodetz, 1970Sodetz, , 1972 and an increase in the probability of emission for long IRTs (Morgan & Mitcehll, 1969;Sodetz, 1970Sodetz, , 1972. In addition there is a reduction in the amount of "bursting" as indexed by the reduced probability of short IRTs.…”

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confidence: 99%

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Conditioned acceleration and free-operant wheel-turn avoidance following septal lesions in rats

Dickinson

Morris

1975

Free·operant wheel·turn avoidance performance of rats with septal lesions and controls was studied in detail. Septal damage decreased the overall response and shock rates and the vigor of the "burst" pattern of responding. Both groups of rats were then given a series of Pavlovian conditioning trials in a separate apparatus. During these sessions, a 5-sec tone was followed by an unavoidable shock on half of the trials and by a 5-sec light stimulus on the remaining trials. Subsequently these stimuli were presented while the animals responded on the free-operant wheel-turn avoidance schedule. The magnitude of the response-rate acceleration produced by the tone in both groups was unaffected by the lesion_ The light did not develop rate-inhibiting properties in either group of animals. These results provide no evidence that septal damage attenuates Pavlovian fear conditioning.

“…Van Hoesen, MacDougall, and Mitchell (1972) have shown that animals with septal lesions are more efficient than normal animals on a two-bar ratio schedule where a high response output is required . Morgan and Mitchell (1969) and Sodetz (1970) have shown that rats with septal lesions are superior to normal animals when performing on a Sidman avoidance schedule. Since performance on these tasks presumably requires the use of responseproduced cues, such findings are inconsistent with the notion that septal damage leads to a deficit in the use of response-produced cues.…”

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confidence: 99%

Internal and external cue use following septal ablation in the rat

Kratz

Mitchell

1977

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As a result of a proposed response-produced cue deficit in rats with septal damage, an attempt was made to determine whether rats with such damage would be overly dependent on exteroceptive cues. Normal and septallesioned rats were trained to perform a behavioral chain where both exteroceptive and response-produced cues could be used. During extinction, these two sets of cues were placed in conflict in order to determine their relative contributions to performance of the chain. Septal rats primarily used response-produced cues, whereas normal animals randomly used the available cues. It was concluded that normal and septallesioned rats differed in their use of external and internal information, but in a direction opposite to that suggested by the literature. Ellen and Butter (1969) have demonstrated that the addition of a cue light significantly improves performance of rats with septal lesions on a task requiring low rates of responding (DRL). Since the cue light signals the end of the required delay of responding, they conclude that the septal deficit on DRL schedules is the result of an inability of these animals to use the response-produced, proprioceptive stimuli used by normal animals . We have demonstrated in our own laboratory (Mitchell & Kratz, Note 1) that, unlike normal rats, septal-lesioned rats which are deficient in two-bar ratio performance (Ellen & Kelnhofer, 1971) are facilitated by the addition of external cue lights. Srebro's (1974) study of retention deficits in successive position reversals indicates that the addition of a visual cue also improves performance of rats with septal lesions on this task. Srebro further shows that the saliency of the visual cue with respect to its correlation with the position reversal will systematically improve performance on the task as saliency increases. Thomas (1972), in a thorough investigation of spontaneous alternation, was able to determine that rats with septal lesions consistently choose to respond to external sensory rather than internal somatomotor cues. Each of these studies demonstrates the septal-damaged animal's increased dependency on external information and support Ellen and Butter's hypothesis. In agreement with this hypothesis, reviews by Lubar and Numan (1973) and Caplan (1973) produced cues. A number of studies, however, indicate that rather than being deficient in their use of internal information, animals with septal area lesions are quite efficient in their use of these types of cues. Van Hoesen, MacDougall, and Mitchell (1972) have shown that animals with septal lesions are more efficient than normal animals on a two-bar ratio schedule where a high response output is required . Morgan and Mitchell (1969) and Sodetz (1970) have shown that rats with septal lesions are superior to normal animals when performing on a Sidman avoidance schedule. Since performance on these tasks presumably requires the use of responseproduced cues, such findings are inconsistent with the notion that septal damage leads to a deficit in the use of response-...