The placebo effect and the autonomic nervous system: evidence for an intimate relationship

Abstract

For many subjectively experienced outcomes, such as pain and depression, rather large placebo effects have been reported. However, there is increasing evidence that placebo interventions also affect end-organ functions regulated by the autonomic nervous system (ANS). After discussing three psychological models for autonomic placebo effects, this article provides an anatomical framework of the autonomic system and then critically reviews the relevant placebo studies in the field, thereby focusing on gastrointestinal, cardiovascular and pulmonary functions. The findings indicate that several autonomic organ functions can indeed be altered by verbal suggestions delivered during placebo and nocebo interventions. In addition, three experimental studies provide evidence for organ-specific effects, in agreement with the current knowledge on the central control of the ANS. It is suggested that the placebo effects on autonomic organ functions are best explained by the model of 'implicit affordance', which assumes that placebo effects are dependent on 'lived experience' rather than on the conscious representation of expected outcomes. Nevertheless, more studies will be needed to further elucidate psychological and neurobiological pathways involved in autonomic placebo effects.

Placebo interventions, placebo effects and clinical practice

“…[32][33][34][35][36]) for mixing highly heterogeneous studies with control interventions, which might not always be considered placebo, for including studies in which all study groups including the no-treatment group received basic treatment with potential impact on the outcomes measured, as well as for a variety of other reasons. Furthermore, subsequent analyses have provided evidence that a subset of studies with outcomes regulated by the autonomic nervous system is susceptible to placebo treatments ( [37]; see also [38]). However, the overall conclusion that available trials including both a placebo and a no-treatment group do not provide convincing evidence for powerful placebo effects in general remains adequate.…”

Introduction to placebo effects in medicine: mechanisms and clinical implications

“…Inspired by the insights stemming from hypnosis research, Kirsch [26] wondered about the underlying psychological function determining the specific response to a suggestion, and he began to focus on the role of expectancy as a mediating psychological variable. The importance of verbal suggestions and expectations for placebo and nocebo effects has meanwhile been demonstrated in numerous experimental studies [22,[27][28][29]. Furthermore, there is now compelling evidence for the validity of classical conditioning theory for explaining placebo effects, because drug-like effects also occur when active treatments administered repetitively are replaced with pharmacological inert interventions such as saline solutions or sugar pills [24,27,30].…”

“…For example, placebo interventions targeting the stomach affected gastric motility, but not cardiovascular or electrodermal functions [61]. She proposes that verbal suggestions during placebo interventions may activate association networks in the brain that store memories of the appropriate autonomic response [22].…”

“…Karin Meissner [22] reviews the placebo literature with respect to the cardiovascular, the gastrointestinal and the pulmonary systems and provides relevant background information on the functional organization of the ANS and the central autonomic network. In accordance with previous findings from analgesic placebo research [59,60], her results provide first evidence for the autonomic specificity of autonomic placebo effects.…”

“…Additionally, there is a bulk of studies showing that organ functions regulated by the autonomic nervous system (ANS) are amenable to both placebo and nocebo interventions [22]. For example, the majority of studies scrutinizing the nocebo effect have actually been investigated in asthmatic patients, and there is now clear evidence that the expectation of bronchoconstriction impairs lung function.…”