The progressive ratio procedure is used across fields to assess motivation for different reinforcers, define the effects of experimental interventions on motivation, and determine experience‐dependent changes in motivation. However, less is known about how operant training schedules affect performance on this widely utilized task. Here we designed an experiment to examine the effect of variable ratio versus fixed ratio training schedules of reinforcement on progressive ratio performance while holding other performance variables constant between groups. We found a robust increase in maximum ratio completed between the pretest and posttraining test highlighting a robust training effect on progressive ratio performance. However, it did not matter if the training was under a fixed or variable ratio schedule. Additionally, we show that neither individual rates during training nor extinction responding correlated with maximum ratio achieved during the sessions. Finally, we show that rates during the training sessions do correlate with extinction performance, suggesting that these variables measure a different aspect of performance that does not predict motivation.

Small bipedal hoppers, including kangaroo rats, are thought to not benefit from substantial elastic energy storage and return during hopping. However, recent species-specific material properties research suggests that, despite relative thickness, the ankle extensor tendons of these small hoppers are considerably more compliant than had been assumed. With faster locomotor speeds demanding higher forces, a lower tendon stiffness suggests greater tendon deformation and thus a greater potential for elastic energy storage and return with increasing speed. Using the elastic modulus values specific to kangaroo rat tendons, we sought to determine how much elastic energy is stored and returned during hopping across a range of speeds. In vivo techniques were used to record tendon force in the ankle extensors during steady-speed hopping. Our data support the hypothesis that the ankle extensor tendons of kangaroo rats store and return elastic energy in relation to hopping speed, storing more at faster speeds. Despite storing comparatively less elastic energy than larger hoppers, this relationship between speed and energy storage offer novel evidence of a functionally similar energy storage mechanism, operating irrespective of body size or tendon thickness, across the distal muscle-tendon units of both small and large bipedal hoppers.

Catecholaminergic systems are involved in a range of psychiatric disorders and are central mediators of the effects of stimulants on the brain and behavior. Advances in analytical detection methods paired with creative application of these approaches allow for recording noradrenergic and dopaminergic systems in the brain in isolation with subsecond resolution. Pauly et al. (ACS Chem. Neurosci. 2023, 10.1021 define the distinct and differential mechanisms of methamphetamine enantiomers on dopamine and norepinephrine release, giving critical insights into the pharmacodynamic properties of a stimulant that is both abused and used clinically.