Despite the vast placebo/nocebo literature, expectations are not typically manipulated directly and are often discussed in unison with an inert agent. Expectations seem to have a role in illness beyond the delivery of (fake) treatments. This situation leaves some ambiguity when the findings on placebo effects apply and when they do not. For this reason, it could be relevant to isolate a specific model, that specifically refers to the expectations that a person has toward his/her illness. I suggest to define this construct “Illness Expectation” (IE). IE is the cognitive schema that defines the expected characteristics of the disease progression and future-oriented beliefs about the symptoms. Like other expectations [20], IEs can manifest as explicit (conscious) future-directed cognitions, or they may be implicit, without an individual’s full awareness. There could be a certain level of overlap between conscious and unconscious processes [31], but though they do not necessarily converge. For example, a person can be well-informed about the expected trajectory of his/her disease, but it is also possible that, implicitly, (s)he represents future developments of the symptoms in a different way. The expectations are based on the supposed knowledge about the diagnosis and the illness [32]. They are therefore influenced by the information received, as well as by the cognitive and emotional elaboration processes, which rely on personal history and skills. Verbal information, patient-clinician interactions, and prior experiences or previous conditioning, as well as personality and other psychological factors (e.g., optimism) may influence the expectation creation, similar to how they influence the placebo response [33, 34]. Illness Expectations could be seen as a specific form of response expectancy, defined by Kirsch [35] as the anticipation of non-volitional responses.
As with other psychological constructs, IEs reflect individual differences, that is, people with the same diagnosis and who have received similar information may have different expectations. The same psychological traits that influence the development of the treatment expectations, which may module the placebo response, may be involved in the characterization of Illness Expectations. For example, it is possible that optimism and spirituality have a positive impact, which would be in line with the positive associations found with these two variables and health [36]. At the same time, social and contextual aspects, such as the patient-physician relationship and trust, social support, could play a role in modulating the expectations. Future studies are required to understand the possible role of these variables.
A crucial factor that mediates the effects of IE is cognitive rigidity. As a cognitive schema, expectations may additionally incorporate different degrees of rigidity, ranging from a mild expectation to a very strict conception of what “will” happen in terms of disease progression. The concept of rigidity, in this context, refers to an inability to maintain a dynamic view of one’s status, effectively keeping evaluations static over time [37]. In other words, rigid IE tend to be very emphatic and resistant mental sets, which could be similar to certain core beliefs in the cognitive-behavioral approach [38]. It is effectively a form of mindlessness, in which an idea is unchanged over time even with changes in situation or context [39, 40]. Cognitive rigidity, which is the reverse of cognitive flexibility, is generally considered a stable characteristic over time [41]. Similar to flexibility, however, rigidity could change over time, for example as a result of a psychological intervention [42].
Under the lens of the Illness Expectation model, the placebo response is not necessarily the arising of new, treatment-related expectations, but it could represent the modification of a previously existing mindset. However, the IE effects are not limited to placebo responses. Placebos are an external manipulation, often achieved with some form of ambiguity or deception (e.g., a “fake” pill), while IEs are self-created, although they can be influenced by external manipulations (e.g., doctor’s opinions, information from other patients).
It is here suggested that IE could influence symptoms and disease progressions (i.e., medical outcomes) with two ways: a behavioral way and a non-behavioral way (Fig. 1). The former refers to behavioral changes, including adherence to the treatment and lifestyle (physical activity, eating habits…) modifications. The non-behavioral way refers to the physiological changes “directly” influenced by the expectations, mirroring the placebo/nocebo effect, but observed without a primer.
While expectations and rigidity focus emphasize the cognitive level of the mind/body interaction, emotions and stress can also interact with the process, with different pathways. Emotions (e.g., fear) could influence both implicit and explicit expectations. They could lead to behavioral changes, and direct effects of negative emotions on the body (e.g., immune system) are documented [29]. A peculiarity of this model is the role of rigidity, which could represent a clinical target for psychological interventions. There are several psychological approaches that could improve flexibility and discourage rigid thinking. Future studies could explore how these interventions could modify the IE effects on the body.
The IE model, at the present, is based on indirect evidence from the scientific literature and organized through this theory. Empirical studies are warranted to test its validity and provide direct data-driven conclusions. One of the first problems that should be addressed by this field is the development of tools for the expectation assessment. While there are existing instruments that assess expectations, most of them focus on treatment expectations. For example, The Credibility/Expectancy Questionnaire [43] explores treatment credibility and expectancy, while the Stanford Expectations of Treatment Scale [44] considers both positive and negative expectations. Although very important, treatment expectancies do not inglobe the illness expectations as a whole. Furthermore, considering the potential role of both implicit and explicit components, self-reported measures may not be able to fully assess the construct. The use of instruments to assess implicit components should be considered. Studying the effects of IE manipulations on the body may provide important confirms/disconfirms to the mind/body connection hypothesis, with the potential to lead to several clinical implications. Perhaps the most important and ambitious one would be a better understanding of how we can use a mechanism similar to the placebo effect, without the ethical burden of deception. The meaningful use of the placebo effect without deception has been suggested as a highly relevant research topic in psychology [3]. It could push to the limits our current understanding of the mind/body connection, with yet to be explored opportunities for clinical interventions.