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The saccadic oculomotor circuit as a CPG: Neuronal activity during cyclic “stepping”
Author(s) -
Gnadt James W
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a463
Subject(s) - microstimulation , neuroscience , brainstem , central pattern generator , saccadic masking , eye movement , saccade , computer science , psychology , stimulation , physics , rhythm , acoustics
The saccadic eye movement circuit in the brainstem of mammals appears to operate as a recurrent, closed‐loop network similar to the central pattern generators (CPGs) of the spinal cord and brainstem. Normally, voluntary effort engages the circuit for one stereotyped movement. However, prolonged experimental activation reveals cyclic movements, called “staircase saccades” that “walk” with a frequency proportional to the input intensity. Systematic study of this CPG‐like behavior with experimental activation by microstimulation has produced benchmark comparisons for testing control system models and for mechanistic predictions at circuit and cellular levels. One of our predictions involved the functional relationship of an inhibitory cell group called omnipause neurons (OPNs) that are thought to hold the high‐gain circuit in check when the eyes are not moving. They are tonically active except for transient pauses during saccades. By using a new noise cancellation technique to record during prolonged microstimulation, we have shown that the OPNs do not pause throughout the prolonged stimulation as some theories had predicted, but instead repeatedly pause and reactivate during the periodic movements. This conclusively demonstrates that the OPN are part of the intrinsic CPG for generating saccades and not a simple permissive side‐loop – for example, as part of an active ocular fixation circuit. JWG is supported by NEI (R01‐EY015870, R03_EY016234) and NINDS (U54_NS039407) .