FBS Colloquia No.402Dynamic Brain Network Laboratory

Error signals in the parvocellular red nucleus drive adaptation in reaching

Errors in reaching drive trial-by-trial adaptation to compensate for the error. Our recent studies demonstrated that motor cortices and parietal areas provide error signals that drive trial-by-trial adaptation in reaching movements (Inoue et al. 2016; Inoue and Kitazawa 2018). However, these results do not necessarily indicate that adaptation takes place within the cerebral cortices. It is possible that adaptation would rather take place in the cerebellum after the error signals are conveyed to the cerebellum. First, adaptation is impaired by dysfunctions of the cerebellum. Second, error signals are actually encoded by climbing fibers (Kitazawa et al., 1998). Assuming that the hypothesis is true, the parvocellular part of the red nucleus (RNp), which receives inputs from the cerebral cortices and sends output to the inferior olivary nucleus, should be playing a key role in adaptation. To test the hypothesis, we recorded neuronal activities in the RNp while two monkeys made a rapid reaching movement toward a visual target that appeared at a random location on a tangent screen. We found that approximately half of the RNp neurons encoded information on target positions before the onset of movement and/or visual apparent error after the end of movement. These results were similar to those of complex spikes of Purkinje cells (Kitazawa et al. 1998). The latency of information on the apparent error in the RNp was longer than those in the motor cortices and parietal area 5, suggesting that the information originated in the cerebral cortices. We then delivered electrical microstimulation to the RNp after the touch. Repetitive paring of reaching movements with microstimulation produced a gradual and significant increase of the end-point error opposite to the preferred direction of visual apparent error. These results suggest that the RNp receives information on the visual apparent error from the cerebral cortices, and sends error signals to the cerebellum that eventually drive trial-by-trial adaptation in reaching movement.