Figure 14.

Circuit diagram showing the cMRF as a conduit for collicular influence on lower brainstem centers. Connections from the left side of the midbrain that would produce rightward (contraversive) saccades are shown. Neurons located in the cMRF receive direct input from the SGI of the SC and forward a signal to the horizontal gaze center, the brainstem center that controls horizontal saccadic eye movements. The horizontal gaze center contains both excitatory burst neurons (EBNs) and inhibitory burst neurons (IBNs) that are premotor cells projecting to the ipsilateral and contralateral abducens nucleus, respectively. Axons of collicular neurons (blue pentagon) that travel via the predorsal bundle, provide collaterals to the ipsilateral cMRF before crossing and terminating in the horizontal gaze center. The cMRF contains both inhibitory (red circle) and excitatory (blue circle) cells that project to the ipsilateral horizontal gaze center. In addition, it contains a population of cells (purple circle) that project to the contralateral horizontal gaze center. The cMRF also provides feedback to the SC, which is purely inhibitory (red circle), ipsilaterally, and both inhibitory and excitatory (red and blue circles, respectively), contralaterally. The activity of cMRF neurons for rightward (R) and leftward (L) saccades is indicated by small arrows.