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Guiding Binocular Saccades during Reading: A TMS Study of the PPC.

Vernet M, Yang Q, Kapoula Z - Front Hum Neurosci (2011)

Bottom Line: Stimulation had three major effects: (1) disturbance of eye alignment during fixation; (2) increase of saccade disconjugacy leading to eye misalignment; (3) decrease of eye alignment reduction during fixation drift.The effects depend on the side; the right PPC was more involved in maintaining alignment over the motor sequence.The study might be of interest for the understanding of deficits of binocular coordination, encountered in several populations, e.g., in children with dyslexia.

View Article: PubMed Central - PubMed

Affiliation: IRIS Laboratory, CNRS, FRE 3154 and Assistance Publique - Hôpitaux de Paris Paris, France.

ABSTRACT
Reading is an activity based on complex sequences of binocular saccades and fixations. During saccades, the eyes do not move together perfectly: saccades could end with a misalignment, compromising fused vision. During fixations, small disconjugate drift can partly reduce this misalignment. We hypothesized that maintaining eye alignment during reading involves active monitoring from posterior parietal cortex (PPC); this goes against traditional views considering only downstream binocular control. Nine young adults read a text; transcranial magnetic stimulation (TMS) was applied over the PPC every 5 ± 0.2 s. Eye movements were recorded binocularly with Eyelink II. Stimulation had three major effects: (1) disturbance of eye alignment during fixation; (2) increase of saccade disconjugacy leading to eye misalignment; (3) decrease of eye alignment reduction during fixation drift. The effects depend on the side; the right PPC was more involved in maintaining alignment over the motor sequence. Thus, the PPC is actively involved in the control of binocular eye alignment during reading, allowing clear vision. Cortical activation during reading is related to linguistic processes and motor control per se. The study might be of interest for the understanding of deficits of binocular coordination, encountered in several populations, e.g., in children with dyslexia.

No MeSH data available.


Related in: MedlinePlus

Effects of single-pulse TMS on vergence angle during reading saccades and fixations. Sample traces of the disconjugacy (Left eye − Right eye) and the conjugate eye position (Left eye + Right eye)/2 during 1.1 s of reading in the no-TMS, left PPC stimulation and right PPC stimulation for the subjects s5 and s6. Vertical lines indicate the occurrence of a stimulation, at t = 0. Examples were chosen to observe several rightward saccades after stimulation, but TMS could occur at any time during the reading.
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Figure 1: Effects of single-pulse TMS on vergence angle during reading saccades and fixations. Sample traces of the disconjugacy (Left eye − Right eye) and the conjugate eye position (Left eye + Right eye)/2 during 1.1 s of reading in the no-TMS, left PPC stimulation and right PPC stimulation for the subjects s5 and s6. Vertical lines indicate the occurrence of a stimulation, at t = 0. Examples were chosen to observe several rightward saccades after stimulation, but TMS could occur at any time during the reading.

Mentions: Figure 1 shows samples of conjugate eye position and disconjugacy traces during 1100 ms, corresponding approximately to the reading of one line. Inspection of conjugate traces showed no effect of TMS on conjugate aspect of saccades and fixations, neither on saccade amplitude, nor on conjugate drift. Some disturbance after stimulation occasionally occurred (see subject s6, TMS of the left PPC), but such disturbance was rare and TMS had no statistically significant effect on any conjugate parameters (amplitude, duration, and velocity, all the p > 0.05).


Guiding Binocular Saccades during Reading: A TMS Study of the PPC.

Vernet M, Yang Q, Kapoula Z - Front Hum Neurosci (2011)

Effects of single-pulse TMS on vergence angle during reading saccades and fixations. Sample traces of the disconjugacy (Left eye − Right eye) and the conjugate eye position (Left eye + Right eye)/2 during 1.1 s of reading in the no-TMS, left PPC stimulation and right PPC stimulation for the subjects s5 and s6. Vertical lines indicate the occurrence of a stimulation, at t = 0. Examples were chosen to observe several rightward saccades after stimulation, but TMS could occur at any time during the reading.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3037530&req=5

Figure 1: Effects of single-pulse TMS on vergence angle during reading saccades and fixations. Sample traces of the disconjugacy (Left eye − Right eye) and the conjugate eye position (Left eye + Right eye)/2 during 1.1 s of reading in the no-TMS, left PPC stimulation and right PPC stimulation for the subjects s5 and s6. Vertical lines indicate the occurrence of a stimulation, at t = 0. Examples were chosen to observe several rightward saccades after stimulation, but TMS could occur at any time during the reading.
Mentions: Figure 1 shows samples of conjugate eye position and disconjugacy traces during 1100 ms, corresponding approximately to the reading of one line. Inspection of conjugate traces showed no effect of TMS on conjugate aspect of saccades and fixations, neither on saccade amplitude, nor on conjugate drift. Some disturbance after stimulation occasionally occurred (see subject s6, TMS of the left PPC), but such disturbance was rare and TMS had no statistically significant effect on any conjugate parameters (amplitude, duration, and velocity, all the p > 0.05).

Bottom Line: Stimulation had three major effects: (1) disturbance of eye alignment during fixation; (2) increase of saccade disconjugacy leading to eye misalignment; (3) decrease of eye alignment reduction during fixation drift.The effects depend on the side; the right PPC was more involved in maintaining alignment over the motor sequence.The study might be of interest for the understanding of deficits of binocular coordination, encountered in several populations, e.g., in children with dyslexia.

View Article: PubMed Central - PubMed

Affiliation: IRIS Laboratory, CNRS, FRE 3154 and Assistance Publique - Hôpitaux de Paris Paris, France.

ABSTRACT
Reading is an activity based on complex sequences of binocular saccades and fixations. During saccades, the eyes do not move together perfectly: saccades could end with a misalignment, compromising fused vision. During fixations, small disconjugate drift can partly reduce this misalignment. We hypothesized that maintaining eye alignment during reading involves active monitoring from posterior parietal cortex (PPC); this goes against traditional views considering only downstream binocular control. Nine young adults read a text; transcranial magnetic stimulation (TMS) was applied over the PPC every 5 ± 0.2 s. Eye movements were recorded binocularly with Eyelink II. Stimulation had three major effects: (1) disturbance of eye alignment during fixation; (2) increase of saccade disconjugacy leading to eye misalignment; (3) decrease of eye alignment reduction during fixation drift. The effects depend on the side; the right PPC was more involved in maintaining alignment over the motor sequence. Thus, the PPC is actively involved in the control of binocular eye alignment during reading, allowing clear vision. Cortical activation during reading is related to linguistic processes and motor control per se. The study might be of interest for the understanding of deficits of binocular coordination, encountered in several populations, e.g., in children with dyslexia.

No MeSH data available.


Related in: MedlinePlus