Functional MRI of brain activation by eye blinking

Functional magnetic resonance imaging (fMRI) was used to map cortical areas that control eye blinking. T2*-weighted asymmetric spin-echo MRI (or BOLD- blood oxygen level dependent-MRI) was used to detect changes caused by foca l variations in blood oxygenation. Six normal volunteers and two cases of d ry eye (less than 5-mm Schirmer's test) entered the study. The experimental scheme consisted of three cycles of a two-step sequence: (eyes closed)-(bl ink or blink inhibition). And to minimize contamination from photic activat ion, the experiments were carried out in a dark environment and the volunte ers reported no light perception during the MR scans. In all eight cases, normal blinking (about one blink every 4 sec) activated areas in the orbitofrontal cortex and in some cases, the visual cortex inc luding the anterior portion of the visual cortex and the primary visual cor tex. In severe dry eye, blink-inhibition strongly activated the visual cort ex even after irritation due to corneal desiccation was removed by topical anesthesia. The blinking process, especially the rate, appears to be controlled in the orbitofrontal cortex. The significance of visual cortex activation in the d ark and in the case of severe dry eye still remains unclear; although it ma y be associated with attention and arousal. (C) 1999 Academic Press.