Figure 1.
Mutual facilitation of actions from the two pyramids. A, B, Simplified diagrams of connections between pyramidal tract fibers and ipsilateral hindlimb motoneurons, via reticulospinal neurons and commissural interneurons [Edgley et al. (2004), modified from their Fig. 1]. Circles represent RS neurons, lamina VIII commissural neurons (VIII), and hindlimb motoneurons (MN) with which commissural interneurons form synaptic contacts. They show that both the left (L) and right (R) PT fibers may excite RS neurons projecting via the right medial longitudinal fascicle and that these neurons may be excited either monosynaptically or disynaptically (via other RS neurons). C, D, Reconstructions of the locations of the PT and MLF stimulating electrodes, as defined by the electrolytic lesions made at the end of the experiments. These are superimposed on representative sections of the brainstem cut in the plane of the electrode insertions. E-G, Intracellular records from a PBST motoneuron (top traces) and the associated records from the cord dorsum (bottom traces); averages of 20 records. In this and all other figures, the negativity is downward for microelectrode records and upward for records from the cord dorsum. Voltage calibration is for intracellular records.