Tanaka and colleagues in Dr. Matsuzaki’s lab at the University of Tokyo have been researching the role of thalamocortical axonal activity in motor learning using the TaskForcer. 

Brain regions involved in voluntary movement

The thalamus is a central hub through which neuronal signals are transmitted through the cortex and other subcortical structures including the basal ganglia, the pons, and the cerebellum.

Brain regions involved in voluntary motor control (Adapted from Waxman, SG. Clinical Neuroanatomy 26th edition, 2009).

Together, these structures are involved in controlling voluntary movements like manual skills. In animals, manual skills are learned and refined through repetitive motor learning, which instigates neuronal plasticity in the brain structures involved in these processes.

Measuring axonal activity in vivo

Using two-photon calcium imaging of GCaMP expressing thalamocortical axons in the mouse motor cortex in combination with the TaskForcer restraint operant chamber, Tanaka, et al., ascertained the role of thalamocortical axonal activity in skilled motor learning.

The TaskForcer operant chamber fits under the 2P microscope, enabling precise neural imaging during operant training. The task used was a self-initiated lever-pull task, where mice were trained to pull a lever in order to receive a water reward.

By recording calcium activity of GCaMP expressing thalamocortical axons in the motor cortex during learning, they were able to track the temporal dynamics of thalamocortical activity associated with each stage of the learning process.

Linking neuronal activity to coordinated movements

The authors found that thalamocortical activity was time-locked to both initiation and execution of the lever pull task and that this activity stabilized over time after the initial learning. As proof of concept to verify the thalamus’ role in motor learning, when the authors lesioned the thalamus, lever pull behavior significantly decreased. These results indicated that thalamocortical axonal activity is necessary for motor skill learning, and is more involved during the initial stages of motor skill learning.

Example of the lever-pull task using the TaskForcer. (Adapted from Tanaka et al., 2018)

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Check out the full article in Cell here.