The generality of learned helplessness theory: effect of electroconvulsive shock

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Virginia Polytechnic Institute and State University


While the learned helplessness effect has been reliably found in dogs and other species (e.g., cats, mice, fish, and humans), it has been somewhat difficult to obtain in rats. In addition, it has been demonstrated that electroconvulsive shock (ECS) reverses learned helplessness in dogs, but ECS induced reversal has not been demonstrated in the rat. Thus, the purpose of this dissertation was twofold: (1) to determine if the learned helplessness effect could be reliably demonstrated in rats; and (2) if so, will a single ECS attenuate this phenomenon. If it could be shown that ECS attenuates helplessness, then two purposes would be served: (a) it would extend the generality of learned helplessness theory by indicating additional parallels between dog helplessness and rat helplessness; and (b) it would expand the parallels between learned helplessness and human depression, thereby increasing the validity of the learned helplessness model of depression.

In Experiment 1, rats were randomly assigned to one of three groups: escape, yoked-inescapable, and no shock control. Each rat in the escape group received 80 trials of unsignaled escapable shock. The escape group rats were required to perform a progressive fixed-ratio bar press to escape shock. The yoked-inescapable group received exactly the same intensity, frequency, and duration of shock its escape partner received; but no response would escape shock. The no-shock control group received only pre-exposure to the training apparatus. The following day all rats were tested on a FR-2 shuttlebox escape/avoidance task. After test, half the rats in each group were given a single ECS and then were retested 24 hours later in the shuttlebox. The learned helplessness effect was clearly demonstrated during the test phase. In addition, a single ECS attenuated the learned helplessness effect in rats.

In Experiment 2 rats were given training exactly as described in Experiment 1. Following training, one-third of the rats in the escape and yoked-inescapable groups were given a single ECS immediately, one-third were given a single ECS 23.5 hours later, and one-third received no treatment. In the no-shock control group one-third of the rats were given a single ECS 24 hours prior to test, one-third of the rats were given ECS 30 minutes prior to test, and one-third of the rats were not given ECS. Then, all rats were tested 24 hours following training. The test session was identical to the test session in Experiment 1. The learned helplessness effect was clearly demonstrated during test in the NO-ECS condition. In addition, it was demonstrated that ECS attenuates or reverses learned helplessness training when given immediately following training. Delayed ECS also reverses helplessness, but less dramatically than immediate ECS.

In both experiments the criteria which characterize learned helplessness were matched: (1) Failure to initiate the escape response in the presence of shock; (2) failure to maintain escape behavior even after occasional escape response occur; and (3) that conditions 1 and 2 above are a result of inescapability and not a result of shock per se. In addition, since ECS attenuates helplessness, the generality of helplessness theory was extended to rats, and the validity of learned helplessness model of depression was strengthened.