An overnight performance decrement is allegedly characteristic of habits maintained by intracranial electrical stimulation. The decrement was here found to be (a) not common to all electrode sites, (b) reduced by one un-reinforced trial, and (c) reduced by intracranial stimulation administered below a rewarding intensity. The electrode sites not associated with performance decrement were in the median forebrain bundle (MFB). Those associated with decrement were somewhat removed from the MFB, at sites other experiments have shown to be both positively and negatively reinforcing. These findings are discussed in relation to Deutsch's theory of simultaneous drive-induction and reinforcement.
Four rats were found to have conspicuous discrete-trial performance decrements when reinforced in a runway with intracranial stimulation ([CS)Rats reinforced with intracranial stimulation (ICS) are commonly found to exhibit conspicuous discrete-trial performance decrements. Unlike conventional reinforcers, where performance is not drastically affected by manipulations of the intertrial interval, Ss reinforced with ICS commonly exhibit greatly increased reaction times when separated from the stimulation by either time, or perhaps distance. A number of explanations of these performance decrements have been put forth but regardles& of which, if any, of the current hypotheses is most correct, it is important to consider the limiting features of ICS as a reinforcer.One explanation of the decrements was deduced from Deutsch's (1960;Deutsch & Howarth, 1963) structural theory of behavior. Within this framework each ICS excites a "central motivational state" as well as a state of reinforcement. The central motivational state was postulated to decay rapidly when ICS is discontinued, hence the performance decrement is a direct function of time since the last ICS. The Ss are just not "motivated" for ICS.An alternative and more informal explanation can be derived from the work of Olds (1962;Briese & Olds, 1964). It might be assumed that some real confusion of associational processes occurs as a result of stimulation in reinforcing areas. The emotion or motivation engendered by appetitive or aversive ICS results in a disruption of mnemonic processes or obscures an intact mnemonic mechanism.Data from our previous studies (Wasden, Reid, & Porter, 1965;Wasden, 1966) have conflicted with both of these explanations. Importantly, not all of the rats we have tested have shown a discrete-trial performance decrement, even following a lO-day intertrial interval. Some rats did indeed show the decrement but the decrement could be reduced by first administering a nonreinforced trial. We also found a high correlation between sites of stimulation and the presence of the decrement. Rats that were stimulated in the medial forebrain bundle showed little or no decrements, while decrements were shown by rats whose stimulation sites were somewhat removed from the medial forebrain bundle. Those sites associated with decrements were in regions Olds & Olds (1963) have shown to be both positively and negatively reinforcing, depending on rather slight changes in parameters of stimulation. These data, plus other observations, such as the decrement frequently becoming apparent after some training rather than throughout training, led to the speculation that the performance decrement is analogous to behavior seen in studies of approach-avoidance conflict. The present study is a further test of this assumption. If it is avoidant behavior, or fear, that is responsible for the decrement, then administering an effective fear-reducing drug should substantially reduce the decrement. Amobarbital sodium (sodium amy tal) is such a fear-reducing drug (Miller, 1961)...
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