Exploration biases how forelimb reaches to a spatial target are learned

Abstract

The brain can learn to generate actions, such as reaching to a target, using different movement strategies. Understanding how different variables bias which strategies are learned to produce such a reach is important for our understanding of the neural bases of movement. Here we introduce a novel spatial forelimb target task in which perched head-fixed mice learn to reach to a circular target area from a set start position using a joystick. These reaches can be achieved by learning to move into a specific direction or to a specific endpoint location. We find that mice gradually learn to successfully reach the covert target. With time, they refine their initially exploratory complex joystick trajectories into controlled targeted reaches. The execution of these controlled reaches depends on the sensorimotor cortex. Using a probe test with shifting start positions, we show that individual mice learned to use strategies biased to either direction or endpoint-based movements. The degree of endpoint learning bias was correlated with the spatial directional variability with which the workspace was explored early in training. Furthermore, we demonstrate that reinforcement learning model agents exhibit a similar correlation between directional variability during training and learned strategy. These results provide evidence that individual exploratory behavior during training biases the control strategies that mice use to perform forelimb covert target reaches.

Dissociable roles of thalamic nuclei in the refinement of reaches to spatial targets

“…To study the roles of Pf and VAL in the learning and refinement of target reaches, we trained mice (n = 10) in our Spatial Target Task (STT) 33 while we imaged their thalamic neural activity ( Figure 1A/B ). Head-fixed mice explored a 2-dimensional workspace by moving a joystick with their right forelimb from a set start location.…”

“…SCARA joystick hardware and Spatial Target Task controls The SCARA (Selective Compliance Articulated Robot Arm) joystick and rig was built as described previously 33 . Animals were head-fixed in a custom-designed 3D printed cup (copyright IR CU21353), that we have previously shown allows increased workspace exploration compared to the standard tube.…”

“…The training schedule was designed as described previously 33 and included 2 pre-training phases, and 2 blocks of target training. Briefly, pre-training consisted of 4 days of Phase 1, and 5 or more days of Phase 2.…”

“…Here, we investigated how Pf and VAL contribute to the control and refinement of reaches to a target in space, using a head-fixed joystick task that we developed 33 . We used 2-photon calcium imaging of glutamatergic neural populations in the forelimb regions of both areas across time, and uncovered that many neurons change activity during reaches early learning.…”

Cortico-thalamic communication for action coordination in a skilled motor sequence

“…To date, most neural circuit studies in mice have focused on movement parts, e.g. the forelimb 40,43–48 or orofacial movement 49–55 , but not their serial order and coordination across body as an integrated behavior (but see 36,56 ). Here, through high-resolution quantitative analysis of a chemosensory-guided reach and grasp to drink behavior (RGD) 45 , we have revealed the serial ordering and coordination of a set of forelimb (aim, advance, supinate, grasp, withdraw) and oral (mouth open, lick) actions to retrieve water to drink.…”