How the brain obeys Hering's law: a TMS study of the posterior parietal cortex.
OBJECTIVE
Human ocular saccades are not perfectly yoked; the origin of this disconjugacy (muscular versus central) remains controversial. The purpose of this study was to test a cortical influence on the binocular coordination of saccades.


METHODS
The authors used a gap paradigm to elicit vertical or horizontal saccades of 10 degrees , randomly interleaved; transcranial magnetic stimulation (TMS) was applied on the posterior parietal cortex (PPC) 100 ms after the target onset.


RESULTS
TMS of the left or right PPC increased (i) the misalignment of the eyes during the presaccadic fixation period; (ii) the size difference between the saccades of the eyes, called disconjugacy; the increase of disconjugacy was significant for rightward and downward saccades after TMS of the right PPC and for downward saccades after TMS of the left PPC.


CONCLUSIONS
The authors conclude that the PPC is actively involved in maintaining eye alignment during fixation and in the control of binocular coordination of saccades.
Vernet
Marine
M
IRIS Group, CNRS-Collège de France, 11 place Marcelin Berthelot, Paris, France. marine.vernet@especi.org
Yang
Qing
Q
Daunys
Gintautas
G
Orssaud
Christophe
C
Eggert
Thomas
T
Kapoula
Zoï
Z
D000328:Adult; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D010296:Parietal Lobe / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D015348:Vision, Binocular / Q000502:physiology*