DOI: 10.5176/2251-1865_CBP16.17
Authors: Yuen-Siang Ang and Masud Husain
Abstract: Apathy or lack of motivation to act is a profoundly disabling clinical condition that also occurs in milder form in healthy people. The mechanisms underlying its manifestations are largely unknown, but it has been suggested that it might arise from deficits in decision-making. Here we examined the relationship between apathy and (i) option generation, and (ii) option switching in healthy young and older adults. We used two novel paradigms implemented on a touchscreen computer while level of motivation in participants was indexed using a modified version of the Lille Apathy Rating Scale. In the first task, participants (young: n = 40; elderly: n = 26) were required to produce, in four minutes, as many different paths as possible between a start-point and an end-goal. Three conditions were tested, with different levels of effort required (0, 4 or 8 barriers). In each condition, the number of paths generated correlated strongly with motivation, independent of age, baseline motor ability and IQ. In the second task, participants (young: n = 28; elderly: n = 20) had three minutes to maximize rewards earned by producing as many paths as they could, but now they had a choice between two options. Each path was drawn from a startpoint to either a (i) high reward option that became progressive harder to reach with new barriers appearing each time a path was drawn to it, or (ii) low reward option with no barriers. Compared to motivated people, apathetic individuals actually allocated more effort during the task. They persevered longer on going to the high-reward option (which progressively became harder to reach), switching to the easier, low-reward option much later than more motivated participants. Yet, as a result apathetic people earned fewer credits. Using each individual’s movement time to reach the low-reward option, we also computed the optimal number of paths to the high-reward option before a participant should switch to the low-reward option. Deviation from the optimal strategy scaled negatively with motivation level, i.e. apathetic people were less able to initiate effective responses, deviating more from the optimal strategy. These findings demonstrate that lack of motivation is associated with both impaired option generation and option switching goaldirected behavior. Apathetic people were not only slower at generating options, but were also less able to switch effectively between them. These simple tasks serve as tools to probe disrupted decision-making mechanisms underlying motivational deficits, providing objective methods for examining pathological apathy in brain disorders.
Keywords: effort, task-switching, executive control, cognitive control, goal-directed behaviour
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