May 2003
Volume 44, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2003
FMRI Reveals Rebound Activation Lateral to Stimulated Regions of Retinotopic V1
Author Affiliations & Notes
  • C.W. Tyler
    Smith-Kettlewell Eye Rsch Inst, San Francisco, CA, United States
  • C. Chen
    Smith-Kettlewell Eye Rsch Inst, San Francisco, CA, United States
  • C. Liu
    MRI Laboratory, National Taiwan University, Taipei, Taiwan Republic of China
  • Y. Wang
    MRI Laboratory, National Taiwan University, Taipei, Taiwan Republic of China
  • Footnotes
    Commercial Relationships  C.W. Tyler, None; C. Chen, None; C. Liu, None; Y. Wang, None.
  • Footnotes
    Support  NIH Grant EY13025
Investigative Ophthalmology & Visual Science May 2003, Vol.44, 4201. doi:
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      C.W. Tyler, C. Chen, C. Liu, Y. Wang; FMRI Reveals Rebound Activation Lateral to Stimulated Regions of Retinotopic V1 . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4201.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Purpose: Rapid stimulation of retinal regions generates rebound activation in adjacent regions of the visual field. We demonstrate corresponding rebound activation in the BOLD signals from an unstimulated retinotopic region adjacent to the stimulated region. A control study evaluated the effect at slow stimulation rates, where the perceptual rebound effect is much reduced. Methods: The test stimulus contained four 45o checkerboard wedges separated from each other by 45o blank regions set at the mean luminance. The checkerboards were flickering in counter phase at 10 Hz during the presentation. The test stimulus consisted of six periods of alternation with a blank field, which contained only a fixation mark, for a 42s scan session. In addition, a 21s blank period was inserted in the middle and at the end of the session to establish the baseline unstimulated level. Retinotopic activation rotating wedges was established in a separate session with. The BOLD signal was collected with EPI with TR=3.5s, TE=35ms and flip angle =90o on a Brucker 3T magnet. Results: In area V1 (Brodmann area 17), the regions corresponding both to the wedges and to the inter-wedges showed activation highly correlated to the test sequence. However, the correlation was positive in the region corresponding to the wedges while much of the interwedge region showed a significant correlation at about 180° to the stimulation. In a control study, the activation was just as strong in the stimulated regions but largely non-significant in the unstimulated regions. This control establishes that the rebound effect was not a property of the hemodynamics but of the long-range neural interactions. Conclusion: The negative rebound activity in the inter-wedge voxels demonstrates that the activity in the unstimulated region can be influenced by the presence of the test in nearby regions. The 180o phase voxels imply a transient activation of the unstimulated regions around the time of the stimulus offset, corresponding to the dynamic twinkle aftereffect (Hardage & Tyler, 1995, VR) reported by the subjects. Therefore, this study may provide a link between lateral modulation and the dynamic lateral aftereffects.

Keywords: visual cortex • spatial vision • temporal vision 
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