The effect of cue-fading on the DRL performance of septal and normal rats

Abstract

The effect of a cue-light fading procedure on the subsequent noncued performance under a differential-reinforcement-of-Iow-rate schedule (DRL) of food reinforcement was determined for rats with septal lesions and normal rats. Following initial DRL-20 sec training. all animals were trained with a cued DRL schedule in which a light signaled the end of the required delay and the availability of reinforcement. Subsequently. for one-half of the animals. the cue light was abruptly discontinued; for the remainder of the subjects. the cue was gradually faded out over succeeding sessions. Septal animals. which had the cue gradually faded. were more efficient by the end of training than septal animals which had the light abruptly discontinued. Moreover. the former did not differ from normal controls. For septal animals in the Fade grouP. the relative frequency distributions of interresponse times (lRTs) were bimodal. a characteristic of normal animals;-.septal animals which had the cue abruptly terminated. displayed the unimodal distribution of IRTs which is a characteristic of septal animals on the DRL schedule. In summary. the cue-fading procedure completely eliminated the major differences in behavior between normal and septal rats typically observed on a DRL schedule of food reinforcement.It is well documented that septal animals perform less efficiently, i.e., they emit more responses per reinforcement (response/reinforcement ratio) than do normals on a differential-reinforcement-oflow-rate (DRL) schedule (Burkett & Bunnell, 1966;Ellen, Wilson, & Powell, 1964). A DRL schedule requires that the animal not respond for some minimum period of time. At the end of the required interval, a response will deliver the reinforcer; if the response is made before the required time has elapsed, reinforcement is not delivered and the clock is recycled. However, high response/ reinforcement ratios are not an invariant consequence of septal damage. A variety of techniques have been shown to attenuate the inefficiency of septal animals on a DRL schedule. For example, cued DRL (Aitken, 1974;Braggio & Ellen, 1976;Ellen & Butter, 1969) with a light as the cue signaling the end of the required delay has been used to decrease the response/reinforcement ratios. Providing the animal with a wooden block and cardboard to chew (Slonaker & Hothersall, 1972) has also produced more efficient septal performance on the DRL schedule. Braggio and Ellen (1974) press the lever was increased or decreased from a particular value as a function of time since the last response.Regardless of the technique used to reduce the response/reinforcement ratios of septal animals, the effectiveness of such procedures has been limited to the condition when the treatment was applied and did not carryover when the normal DRL procedure was reinstated. That is, performance reverted to the typical inefficient pattern when the additional stimuli were removed. Inasmuch as these response characteristics reappeared, Braggio and Ellen (1976) concluded that an inefficient perfor...

A match-mismatch theory of limbic system function

“…The addition of cues can facilitate the performance of these animals, but it may do so by changing the essential nature of the schedule. Interestingly, the improved performance with the cue is not maintained after its removal unless it is slowly faded out (Ellen, Dorsett, & Richardson, 1977). These deficits tie in very well with the cue processing functions of the septum as outlined here.…”

Impaired acquisition ofDRL operant responding following lesion of the habenular nucleus

“…Consideration should also be given to proposals that deficits in DRL performance do not necessarily imply a deficit in either temporal discrimination or ability to inhibit responding. Suggestions have been made that since septal animals are able to overcome their DRL deficit in the uncued paradigm under certain experimental conditions-for example, gradual fading of cue light (Ellen, Dorsett, & Richardson, 1977), gradual lengthening of the DRL delay (Caplan & Stamm, 1967), provision of a wooden block or cardboard to chew on during the delay (Slonaker & Hothersall, 1972), or altering the force required to depress the lever as a function of time since the last response (Braggio & Ellen, 1974)-deficits in response inhibition are not a primary symptom of septal damage, but rather, are secondary to some other form of deficit. Kramer and Rilling (1970) suggest that successful performance on DRL does not require acquisition of temporal discriminations, that animals could equally well learn to pace responding by emitting chains of ' 'mediating" or "superstitious" behaviors, that is, learn that, to achieve reinforcement, responses must be separated not by a particular time span, but rather by performance of a set sequence of behavioral acts, an idea that forms the basis of the DRO (differential reinforcement of other behaviors) theory of DRL responding.…”

Response suppression on DRL by rats with septal damage.

“…There are now a number of studies which indicate that animals with septal lesions do in fact show evidence of suppressing or inhibiting their responding on operant schedules. Ellen and his associates (Braggio & Ellen, 1976;Ellen & Butter, 1969;Ellen, Dorsett, & Richardson, 1977) showed that when animals with septal lesions are given an exteroceptive cue, which signals the end of the required delay on a DRL schedule, the performance on this schedule is indistinguishable from that of normals. It is clear that animals with septal lesions can inhibit cued responding.…”