Neurohnage 13, Number 6,2COl, Part 2 of 2 Parts 1 m E bL@

SENSORIMOTOR

Event Related fMRI of Eye Blink

Peter Erhard*t, Veit Graml*, Xiaoping HuS, Bernhard Haslinger*, Markus Schwaigert, Bastian Conrad*, Andres 0. Ceballos-Baumann*

*Neurologische Klinik, Technische Universitiit Miinchen, Miinchen, Germany

tNuklearmedizinische Klinik, Technische Universitiit Miinchen, Miinchen, Germany

*Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA

Introduction:

Eye blink is a transient behavior which leads to a very subtle hemodynamic response. In order to conduct an fMIU study of non-serial eye blink, it has to be monitored reliably and accurately. We investigated the feasibility of fMIU of human eye blink using an event related approach with a reduced field of view, that was based on previous PET findings of our group (see poster of Van Eimeren et al.) and EOG for blink detection.

Methods:

Eleven subjects were included in the study. EOG was recorded and post-processed as described elsewhere (1). In short, the ECG-system of the Philips Gyroscan NT scanner was used as an EOG amplifier. Via a custom made interface this signal was recorded together with a sync signal from the MB scanner. Using a pattern subtraction algorithm, the majority of the gradient induced signal can he removed in order to restore the EOG signal. Subjects were presented visually with a small figure that changed from a square to a circle or vice versa with randomized intervals ranging from 7s to 14s. In 3 runs, subjects were asked to briefly blink after each change of the figure (mimic spontaneous blinking). For 3 more runs, subjects were instructed to consciously blink whenever they wanted to, but with a comparable number of blinks as in condition one. 8 coronal slices (6rnrn thick), tilted to be approximately parallel to the central sulcus and centered around the anterior commisure were acquired with a TB of 67Oms using fast EPI. 512 instances were recorded in each run (duration: Smin 45 s). Further parameters: FOV 23 cm, TE 50 ms, matrix 64, alpha 50”. Between functional runs, whole brain EPI images were acquired with the same spatial resolution as the functional scans. High resolution T, weighted images were acquired at the end of each session.

ln data analysis, the timing of blii events was based on EOG recordings. The change of the visually presented figure was &fined as a second type of events, that was also modelled. Data of individual scans were realigned, rotated into an axial framework and normalized based on whole brain EPI and anatomic images. After smoothing, contrast images for each subject and each condition were created and a random effects analysis performed.

Results:

The EOG-recordings of eye movements, a&r preprocessing, unambiguously revealed the exact timing of the blink events. FMRl activation was most prominent in SMA. Activation in primary motor cortices was bilateral but much more pronounced on the right.

Conclusion:

In our study, we investigated single eye blinks in two different conditions: self initiated and externally cued. As we did not expect a very strong hemodynamic response, we resorted to few slices and a relatively short TB in or&r to obtain an optimum balance between the amount of temporal data points and S/N. This is the first event related fMRl study we are aware of, that avoids serial blinking and thus tries to achieve a more natural blinking pattern.

Reference:

1 ISMBM 2000. Abstract # 818

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