Rats' learning of a new motor skill: insight into the evolution of motor sequence learning

Changes in reach-to-grasp behaviour over the course of training in rats

One complex task involving sequence of movements and movement refinement in the rat is the single-pellet reaching task, comprising orientation, transport and withdrawal in sequence. In turn, orientation comprises front wall detection, slot localization and nose poke until reach start. Video recordings of a rat in the reaching box highlighted three stages of temporal training: start of training (ST), forepaw dominance appearance (D) and fully trained (T). Regarding orientation, ST versus D and T presented a significant smaller frequency of approach to the front wall and a significant higher number of whisker cycles and nose touches during slot localization, involving a significant longer Orientation. At the ST stage, 44% of the trials were interrupted after nose poke, and poke took place at significant higher level from the shelf. The shelf was identified only when short whiskers contacted it, but the tongue and both forepaws were used without distinction to reach and grasp the pellet until a forepaw emerged as dominant at D stage. Regarding the temporal features of transport and withdrawal, comparing the D versus T stage revealed a significant longer duration. Finally, successes were significantly higher in T respect to D, meaning that after dominance emergence, more training was still necessary to improve reaching/grasping performance. This study provides evidence that, during training, the rats develop a strategy to obtain the pellets and then refine their movement pattern.

Pattern of novel object exploration in cynomolgus monkey Macaca fascicularis

BACKGROUND

Primates exhibit substantial capacity for behavioral innovation, expanding the diversity of their behavioral repertoires, and benefiting both individual survival and species development in evolution. Novel object exploration is an integral part of behavioral innovation. Thus, qualitative and quantitative analysis of novel object exploration helps to better understand behavioral innovation.

METHODS

To study the pattern of novel object exploration, two different sized balls were sequentially introduced to singly caged cynomolgus monkeys. Two aspects of monkeys' behaviors were analyzed: the types of motor activities in toy playing and whether there is an orderly sequence of such motor activities during novelty exploration.

RESULTS

Four types of behavioral activities (oral contact, gross and fine forelimb motor, and hind limb motor) followed a pattern: first forelimb gross motor and oral contact, followed by forelimb fine motor and hind limb activities. Oral contact appeared to be an important behavior in monkeys' repertoire of novelty exploratory behaviors, both as an early appearing activity, and showing a consistent pattern of high cumulative time for two different novel objects.

CONCLUSIONS

These results provide a profile of novel object exploratory behaviors in cynomolgus monkeys, contributing to a better understanding of this aspect of behavioral innovation.

Motivational state, reward value, and Pavlovian cues differentially affect skilled forelimb grasping in rats

Motor skills represent high-precision movements performed at optimal speed and accuracy. Such motor skills are learned with practice over time. Besides practice, effects of motivation have also been shown to influence speed and accuracy of movements, suggesting that fast movements are performed to maximize gained reward over time as noted in previous studies. In rodents, skilled motor performance has been successfully modeled with the skilled grasping task, in which animals use their forepaw to grasp for sugar pellet rewards through a narrow window. Using sugar pellets, the skilled grasping task is inherently tied to motivation processes. In the present study, we performed three experiments modulating animals’ motivation during skilled grasping by changing the motivational state, presenting different reward value ratios, and displaying Pavlovian stimuli. We found in all three studies that motivation affected the speed of skilled grasping movements, with the strongest effects seen due to motivational state and reward value. Furthermore, accuracy of the movement, measured in success rate, showed a strong dependence on motivational state as well. Pavlovian cues had only minor effects on skilled grasping, but results indicate an inverse Pavlovian-instrumental transfer effect on movement speed. These findings have broad implications considering the increasing use of skilled grasping in studies of motor system structure, function, and recovery after injuries.

A system for automated tracking of motor components in neurophysiological research

In the study of motor systems it is often necessary to track the movements of an experimental animal in great detail to allow for interpretation of recorded brain signals corresponding to different control signals. This task becomes increasingly difficult when analyzing complex compound movements in freely moving animals. One example of a complex motor behavior that can be studied in rodents is the skilled reaching test where animals are trained to use their forepaws to grasp small food objects, in many ways similar to human hand use. To fully exploit this model in neurophysiological research it is desirable to describe the kinematics at the level of movements around individual joints in 3D space since this permits analyses of how neuronal control signals relate to complex movement patterns. To this end, we have developed an automated system that estimates the paw pose using an anatomical paw model and recorded video images from six different image planes in rats chronically implanted with recording electrodes in neuronal circuits involved in selection and execution of forelimb movements. The kinematic description provided by the system allowed for a decomposition of reaching movements into a subset of motor components. Interestingly, firing rates of individual neurons were found to be modulated in relation to the actuation of these motor components suggesting that sets of motor primitives may constitute building blocks for the encoding of movement commands in motor circuits. The designed system will, thus, enable a more detailed analytical approach in neurophysiological studies of motor systems.