Why not try harder? Computational approach to motivation deficits in neuro-psychiatric diseases

Abstract

Motivation deficits, such as apathy, are pervasive in both neurological and psychiatric diseases. Even when they are not the core symptom, they reduce quality of life, compromise functional outcome and increase the burden for caregivers. They are currently assessed with clinical scales that do not give any mechanistic insight susceptible to guide therapeutic intervention. Here, we present another approach that consists of phenotyping the behaviour of patients in motivation tests, using computational models. These formal models impose a precise and operational definition of motivation that is embedded in decision theory. Motivation can be defined as the function that orients and activates the behaviour according to two attributes: a content (the goal) and a quantity (the goal value). Decision theory offers a way to quantify motivation, as the cost that patients would accept to endure in order to get the benefit of achieving their goal. We then review basic and clinical studies that have investigated the trade-off between the expected cost entailed by potential actions and the expected benefit associated with potential rewards. These studies have shown that the trade-off between effort and reward involves specific cortical, subcortical and neuromodulatory systems, such that it may be shifted in particular clinical conditions, and reinstated by appropriate treatments. Finally, we emphasize the promises of computational phenotyping for clinical purposes. Ideally, there would be a one-to-one mapping between specific neural components and distinct computational variables and processes of the decision model. Thus, fitting computational models to patients' behaviour would allow inferring of the dysfunctional mechanism in both cognitive terms (e.g. hyposensitivity to reward) and neural terms (e.g. lack of dopamine). This computational approach may therefore not only give insight into the motivation deficit but also help personalize treatment.

Vagus nerve stimulation increases vigor to work for rewards

“…Moreover, as suggested by preclinical research, stimulation at the left ear exerted stronger effects on vigor when food rewards were at stake. We conclude that taVNS may provide a promising brain stimulation technique to improve motivational syndromes characterized by a lack of vigor to pursue rewards such as apathy (Bonnelle et al, 2015;Husain & Roiser, 2018;Muhammed et al, 2016;Pessiglione, Vinckier, Bouret, Daunizeau, & Le Bouc, 2017) or anhedonia (Cooper, Arulpragasam, & Treadway, 2018;Treadway, Peterman, Zald, & Park, 2015;Treadway & Zald, 2011). These findings also add to the growing literature demonstrating the crucial role of peripheral interoceptive signals in tuning instrumental behavior according to metabolic needs.…”

The Effort Paradox: Effort Is Both Costly and Valued

“…For example, a person might have the ability to perform algebra, but fail to solve simple algebra problems due to insufficient mental effort [5]. Although related, effort is not the same as motivation, which is a force that drives behavior by determining both a direction (e.g., goal) and the intensity or vigor with which this direction is pursued [18,21]. Effort refers to the intensity or amplitude of behavior, but does not refer to any specific goal.…”

“…Another indication that effort is costly comes from the finding that people are often willing to accept fewer rewards to avoid effort [61,62]. That is, just as people discount rewards by their associated delays [63,64], so too do they discount rewards by the amount of cognitive or physical effort required to obtain them (i.e., effort discounting ) [21,65]. …”

“…Despite growing and prominent work in cognitive neuroscience detailing effort’s substantial costs [19–21], it is clear that effort also adds substantial value, both to the products of effort and to effort itself (Table 1). …”

The neuroanatomical and neurochemical basis of apathy and impulsivity in frontotemporal lobar degeneration

“…In parallel with correlative investigations of the neuroanatomical correlates of apathy and impulsivity, we present a computational approach embedded in the decision theory to describe and characterize the co-existence of apathy and impulsivity in FTLD syndromes in terms of latent neurocognitive mechanisms [11,12]. …”