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Cécile Bordier, Michel Dojat, Jean-Michel Hupé; BOLD activation in the visual cortex for spontaneous blinks during visual tasks. Journal of Vision 2010;10(7):902. doi: 10.1167/10.7.902.
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We are usually unaware of the temporary disappearance of the visual scene during blinks, even though blinks cause a large illumination change of the retina, as well as related BOLD responses in the visual cortex (Bristow et al., NeuroImage, 2005). We wondered whether spontaneously occurring blinks (in contrast to blocks of voluntary blinks, op.cit.) triggered significant (possibly contaminating) BOLD responses in standard retinotopic and visual experiments. Methods. We monitored in a 3T scanner the monocular eye signals of 14 subjects who observed 4 different types of visual stimuli, including rotating wedges and contracting/expanding rings, Mondrians and graphemes, while fixating. All stimuli were presented centrally and did not exceed 3 degrees eccentricity. We performed event-related single-subject analyses on blinks. Results. We observed the pattern of activations documented for voluntary blinking, with the strongest activation in the anterior calcarine and PO sulcus. This activation was present for every subject and whatever the visual stimulus. It peaked outside of the regions coding our visual stimuli, but often abutting them. ROI based analysis of the 3-deg central V1 region revealed indeed significant BOLD modulation following blinks. Discussion. We replicated the intriguing finding that blinks activate mostly the periphery of retinotopic areas. Since a blink should trigger both a decrease of BOLD signal (due to luminance decrease) and a BOLD response to the dark transient, the anisotropy of the net BOLD response may be caused by different sensibilities to luminance and transients in the center and the periphery. In that case, we may expect that stimulus response modulations by attention also modulate the net BOLD response to blinks. In any case, our results strongly advocate for systematic monitoring of blinks during fMRI recording, since any correlation, even weak, between the distribution of blinks and a tested protocol could trigger artefactual activities in retinotopic areas.
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