Retrograde Tracing of Macaque Motor Cortex

The materials and methods essentially followed those described previously (Liu et al., 2021 (link)) with minor modifications. Information about each monkey is summarized in Table 1. Four adult rhesus macaque monkeys (Macaca mulatta) were utilized in this study. Retrograde tracers, including cholera toxin subunit B conjugated with Alexa Fluor 488 (CTB-488; Thermo Fisher Scientific, MA), CTB conjugated with Alexa Fluor 555 (CTB-555; Thermo Fisher Scientific), CTB conjugated with Alexa Fluor 647 (CTB-647; Thermo Fisher Scientific), and biotinylated dextran amine 3,000 kDa (BDA; Thermo Fisher Scientific), were employed. Case 1 and Case 4 were previously subjected to separate electrophysiology studies in the motor cortex, and all four cases were involved in a distinct neuronal tracing study with CTBs and BDA injected into the prefrontal cortex of the other hemispheres. However, we consider that these treatments did not influence the results of the current study.