Age-dependent Pavlovian biases influence motor decision-making

<div><p>Motor decision-making is an essential component of everyday life which requires weighing potential rewards and punishments against the probability of successfully executing an action. To achieve this, humans rely on two key mechanisms; a flexible, instrumental, value-dependent process and a hardwired, Pavlovian, value-independent process. In economic decision-making, age-related decline in risk taking is explained by reduced Pavlovian biases that promote action toward reward. Although healthy ageing has also been associated with decreased risk-taking in motor decision-making, it is currently unknown whether this is a result of changes in Pavlovian biases, instrumental processes or a combination of both. Using a newly established approach-avoidance computational model together with a novel app-based motor decision-making task, we measured sensitivity to reward and punishment when participants (n = 26,532) made a ‘go/no-go’ motor gamble based on their perceived ability to execute a complex action. We show that motor decision-making can be better explained by a model with both instrumental and Pavlovian parameters, and reveal age-related changes across punishment- and reward-based instrumental and Pavlovian processes. However, the most striking effect of ageing was a decrease in Pavlovian attraction towards rewards, which was associated with a reduction in optimality of choice behaviour. In a subset of participants who also played an independent economic decision-making task (n = 17,220), we found similar decision-making tendencies for motor and economic domains across a majority of age groups. Pavlovian biases, therefore, play an important role in not only explaining motor decision-making behaviour but also the changes which occur through normal ageing. This provides a deeper understanding of the mechanisms which shape motor decision-making across the lifespan.</p></div

Age-dependent Pavlovian biases influence motor decision-making

Decisions in everyday life often require weighing the probability of successfully executing an action (e.g., successfully crossing a street) against potential rewards and punishments. Although older individuals take fewer risks during such motor decision-making scenarios, the underlying mechanism remains unclear. Similar age-related changes in economic decision-making are explained by a decrease in Pavlovian attraction toward reward. However, despite the role of Pavlovian biases in linking action with reward and avoidance with punishment, their impact on motor decision-making is unclear. To address this, we developed a novel app-based motor decision-making task (n=26,532). We found that motor decision-making was subject to Pavlovian influences. Although we found age-related changes for both punishment and reward-based decision-making processes, the most striking effect of ageing was a decrease in the facilitatory effect of Pavlovian attraction on action in pursuit of reward. Using data from an independent economic decision task in the same individuals (n=17,220), we demonstrate similar decision-making tendencies for motor and economic domains across a majority of age groups. Hence, Pavlovian biases play an essential role in not only explaining motor decision-making behaviour but also the changes which occur through normal ageing

Cognitive And Sensorimotor Interactions In Human Decision-Making Within A Virtual Environment

There is a long tradition of studying economic decision making, where humans often fail to maximise expected gain. More recently, attention has been directed towards decision making in mathematically equivalent sensorimotor tasks, where humans often approach maximum expected gain. But numerous everyday tasks have ‘cognitive’ and ‘sensorimotor’ costs. This raises a fundamental, but hitherto neglected research question about the factors that influence decision making when an economic choice has sensorimotor risks. We created a ‘game’ in virtual reality where participants needed to hit targets in order to win points. The game required participants to choose between two targets where one was easier to hit (closer and on permanent display) and the alternative was a harder-to-hit ‘risky’ target worth more points (further away and programmed to time-out). The time allowed to hit the ‘risky’ target was the median of the individual’s baseline trials. Participants deceased their movement time during the baseline trials so the risky targets were more likely to be hit than not regardless of their distance (this resulted in the risky targets having a higher expected gain with respect to the extrinsic reward). In Experiment 1, we found participants (n = 40) were motivated by the reward (so frequently selected the higher value target). Nevertheless, the behaviour was also influenced by the sensorimotor costs, such that participants were more likely to choose the safe option (despite this decreasing expected gain) when the high reward target (worth twice as many points) was further. We found gender differences whereby women were less likely to reach for the high reward target when it was further away. Subsequently, the same selection frequencies were found in two separate groups (both n = 40) despite the high reward target having three and five times more points than the safe option, suggesting that a sensorimotor cost threshold acts as an upper bound on the selection choice process. In Experiment 2, we added motor noise whilst keeping the expected gain constant and found that this manipulation did not affect decision making (i.e. we found same selection frequencies as in Experiment 1). In Experiment 3, we added perceptual noise and again found that this did not affect the decision making. Experiments 2 and 3 suggest that adults are well tuned to the costs of their sensorimotor actions. The data from all 200 participants showed a bias to: (i) select a risky target after a safe trial; (ii) select a risky target after a high reward target was hit (compared to when it was missed). These behavioural phenomena are well captured by a partially observable Markov decision process (pom-dp), and a pom-dp model was able to capture the behaviour by integrating extrinsic rewards and sensorimotor costs in a choice selection process. The pom-dp predicted that participants should increasingly select the risky target across multiple sessions, with the result that males and females should converge on similar selection rates across the different target distances. Experiment 4 tested this prediction with participants repeating the task across multiple sessions over three days. This resulted in an increased probability of the high reward target being selected, and by the end of the sessions the gender differences were not observed. The first four experiments always contained a known ‘safe’ target so Experiment 5 introduced a selection task where the choices needed to be made in a more dynamic fashion and there was not always an obvious ‘safe’ target. Experiment 5 confirmed that participants rapidly combine extrinsic rewards and sensorimotor costs in order to choose between targets on a trial-by-trial basis. Experiment 6 investigated decision making in younger children and showed that the combination of extrinsic rewards and sensorimotor costs occurs in even 7-8 year old children (though there was greater evidence of sub-optimal selections occurring on some trials when the age of the group was younger)

The Influence of Age and Electrical Nerve Stimulation on Motor Function

This dissertation comprises five experimental studies that investigated changes in manual dexterity across the lifespan and the effects of electrical nerve stimulation on motor function and muscle activity. Three studies evaluated associations between neuromuscular characteristics and performance on the NIH Toolbox measures of manual dexterity, and two studied the effects of electrical nerve stimulation on changes in motor function and muscle activity. The first two studies measured neuromuscular differences in middle-aged and older adults, and used performance metrics to identify age-specific associations with manual dexterity. The first study provided a tractable framework to identify latent variables underlying age-associated differences in time to complete the 9-hole and grooved pegboard tests. Mechanisms of interest included neuromuscular characteristics, cognitive function, and cutaneous sensation. The second study expanded these measures to include assessments of risk behavior and muscle activation characteristics. Significant associations were unique for each age group and pegboard test with features derived from force-matching tasks and utility of the reward providing the greatest explanatory power. The third study assessed grooved pegboard timing and force characteristics of peg manipulation for persons with multiple sclerosis and age-and sex-matched healthy adults. Results from this study showed that grooved pegboard time for individuals with multiple sclerosis was most associated with the time to select a peg, whereas times for healthy controls were most related to peg transportation and selection. The last two studies examined the effects of electrical nerve stimulation on force production, muscle activation characteristics, and functional outcomes. The fourth study showed that the immediate effects of electrical nerve stimulation on force and motor unit activity of the contralateral limb were present after stimulation. Lastly, an intervention of electrical nerve stimulation applied to the calf muscled improved mobility, where motor unit discharge characteristics during steady contractions partially explained differences in mobility among older adults. This dissertation explored the changes in motor function and muscle activity with advancing age and the modulation of motor function with electrical nerve stimulation