The hypothesis that early social isolation results in long-term alterations in dopamine receptor sensitivity was tested using older adult rhesus monkeys. Isolated and control monkeys were challenged with apomorphine (0.1 and 0.3 mg/kg), and the drug effects on spontaneous blink rate, stereotyped behavior, and self-injurious behavior were quantified using observational measures. Monoamine metabolites were quantified from cisternal CSF by HPLC-EC, prior to pharmacological challenge. Isolated and control monkeys did not differ in CSF concentrations of HVA, 5-HIAA, or MHPG. At the higher dose, apomorphine significantly increased the rate of blinking, the occurrence of whole-body stereotypies, and the intensity of stereotyped behavior (as measured by observer ratings) in isolated monkeys. The frequency of occurrence of self-injurious behavior was too low to allow for meaningful comparisons. These significant differences in response to apomorphine challenge support the hypothesis that long-term or permanent alterations in dopamine receptor sensitivity, as assessed by drug challenge, are a consequence of early social deprivation.
Past research has indicated that with regard to performance in formal learning test situations, early socially isolated rhesus monkeys display atypical reactions to noxious stimuli, deficits in response inhibition, slower adaptation to reinforcement contingencies, and lower performance on oddity tasks. Twelve adult rhesus monkeys (Macaca mulatta), 6 who had been reared in total isolation for the first 9 months of life 19 years earlier, and 6 socially reared, were tested in a sensory preconditioning paradigm. In phase I, two neutral stimuli (S1-S2) were paired in contiguous fashion; in phase II the S2 stimulus was conditioned to elicit a startle response; and in phase III the S1 stimulus was presented to assess whether an association between the two stimuli had been formed during the initial phase. Instead of a deficit, isolate subjects showed significantly more response transfer during phase III as compared to the controls. The superior performance displayed by isolates is viewed as resulting from a slower habituation to S1-S2 stimuli during preconditioning along with the perseveration of responses during testing. These findings support the notion that atypical cognitive processing across a lifespan is a consequence of early social impoverishment.
Nine isolate and 6 socially reared adult rhesus monkeys were examined in a standard blocking procedure. A tone was paired with a startle stimulus (US) during Phase 1. A tone-light compound CS was paired with a US during Phase 2. In Phase 3, the light was presented alone to test for blocking. Results showed that learning about the light was blocked in social controls, but not in isolates. These data suggest isolates processed information atypically, in that they developed an association to a redundant cue. A second group of isolates (n = 3) underwent the identical procedures. However, conditioned reactions to the tone were extinguished before testing. Test responding was significantly reduced in this group, that is, blocking was obtained. These data suggest the within-compound association developed during Phase 2 mediated the isolate blocking deficit. Together, these findings imply long-term intellectual consequences of early social impoverishment. Such deficits may be mediated by alterations in central dopamine systems.
tereotyped behavior involves rhythmic and topographically invariant S motor acts that occur without obvious eliciting stimuli and have no clearly established function for the biological organism (Lewis & Baumeister, 1982;Ridley & Baker, 1982). The rhythmic and topographically invariant nature of stereotypies has been strikingly depicted in analog tracings of the stereotyped body rocking displayed by individuals with mental retardation, transduced using a single plane accelerometer (see ). Berkson (1983 has argued that the rhythmic or periodic nature of stereotyped behavior may be its most dramatic feature. The apparent "purposelessness" or lack of function of stereotyped behavior, although at the heart of its definition, is less easy to establish, however. Many functions have been posited for stereotypies, including reward, stress reduction, sensory stimulation, and amelioration of an impoverished environment (see recent reviews by Mason, 1991). Some evidence exists to support all of these hypothesized functions. For example, the persistence of stereotypies, even in the face of aversive consequences, has been taken by some as evidence of the rewarding nature of the behavior. Indeed, there
The majority of learning explanations of self-injurious behavior (SIB) have emphasized the control of operant or reward contingencies. Experiment 1 showed that SIB could be elicited in four socially isolated rhesus monkeys (Macaca mulatto) by the application of brief, mild, electric foot shock. In Experiment 2, the three socially isolated monkeys in the experimental group were exposed to a procedure that paired a 10-s tone with a 1-s electric foot shock. Three control monkeys received presentations of the tone alone. Results showed that monkeys in the experimental group began to show SIB during the tone periods, thereby providing evidence of respondent conditioning. These data serve to expand the scope of the learning model of SIB from primarily operant interpretations to respondent conditioning as well.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.