Intracranial stimulation: Performance decrements and a fear-reducing drug

Abstract

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)...

Evidence for a conflict interpretation of anomalous effects of rewarding brain stimulation.

“…(Caution is, of course, required in inferring that the effects of tailshock and brain stimulation are similar, even though they may produce the same behavioral results.) The conflict hypothesis is further supported by Wasden and Reid (1968) who found that a fearreducing drug eliminates the overnight decrement.…”

“…Closer inspection of the behavior of our animals suggested instead that stimulation of most, if not all, areas of the brain may induce concurrent positive and negative effects, and that behavior may be determined by the relative intensity of the two components. A series of experiments was designed to (a) verify the existence of apparently different responses to "rewarding" brain stimulation; (b) determine the nature of the difference in several test situations; and (c) test the adequacy of our hypothesis and related ideas such as Wasden and Reid's (1968) conflict hypothesis.…”

An incentive model of rewarding brain stimulation.

“…Furthermore, reports of human 5"s describe 8 Although histological comparisons are difficult to make, the Ball and Adams (196S) data may be further interpreted in light of the report by Wasden, Reid, and Porter (1965) that overnight decrements in responding are found only from electrode sites which are anatomically removed from the medial forebrain bundle, in areas that have been reported to contain aversive components during stimulation. More recently Wasden and Reid (1968) presented evidence that the approach-avoidance conflict confronting animals with such electrode placement is the cause of the overnight decrement in responding, and that sodium amytal, a fear-reducing drug, eliminates this decrement.…”

Intracranial reinforcement: Performance decrements as a function of stimulus parameters

“…Evidence contradictory to Deutsch's ideas of intracranial reinforcement is plentiful: (a) discrete trial performance decrements may not be present (Wasden, Reid, & Porter, 1965;Wasden, 1966;Scott, 1967;Wasden & Reid, 1968), nor do all investigators fmd it necessary to start their Ss performing with "free trains" of ICS (Kornblith & Olds, 1968), (b) training for ICS on lengthy temporal schedules of reinforcement has been accomplished (Pliskoff, Wright, & Hawkins, 1965), and (c) extinction may not be rapid nor time-dependent, especially when the contingencies of reinforcement are similar to the circumstances of extinction with conven-Psychon. Sci., 1969, Vol.…”