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Hu, Yanbo and Walker, Robin (2018) The investigation of saccade parallel programming using a novel double-step paradigm: an fMRI study. In: Human brain mapping, 17-21 June 2018, Singapore.
Introduction:
This study investigated the neuronal mechanisms of saccade target remapping and decision- making process in relation to parallel programming of saccades. Our previous study (Hu & Walker, 2011) showed that the frontal and parietal eye fields were both involved in pre-programmed of saccade sequences. It has been suggested that the representation of the second saccade goal in the double-step paradigm may involve the process of saccade target re-mapping (Duhamel, Colby, & Goldberg, 1992). In this study, we have developed a novel double-step paradigm enable us to be able to examine the neuronal mechanism underlying saccade target remapping process that required for second saccades to be executed correctly.
Methods:
Fifteen participants completed a novel double-step task in a 3T MRI scanner. Anatomical scans (T1 weighted) were acquired for each participant before the functional scans (TR = 1830 ms, TE = 5.5ms, resolution = 256*256, flip angle of 11°, number of slices = 160, field of view = 256*256). Functional data were collected from the whole brain using echo-planar (EPI) images with voxel size of 3*3*3 mm (TR = 3000 ms, TE = 32 ms, resolution = 64*64, field of view = 192*192, flip angle = 90°, number of slices = 42). For each participant, 73 volumes were acquired in an interleaved sequence per session.
Different double-step saccade trials were as follows: 1) saccades required both target remapping and change-of-plan (saccade to an alternative target); 2) saccades required target remapping but no change-of-plan; 3) saccades required change-of-plan but not target remapping (when a return saccade to the origin or a saccade to an alternative target with vector the same as the original one was made); 4) saccades required neither target remapping nor change-of-plan. Contrasting the BOLD signal between these trial types examined the neural basis of the saccade target remapping and change-of-plan processes.
Results:
FMRI data were analyzed using SPM5 (functional imaging laboratory, UCL, 2005) based on Matlab 6.5 (The MathWorks, 2002). Realignment (2nd Degree B-Spline interpolation), normalization (MNI space) and spatial smoothing (8mm Gaussian smoothing kernel) were carried out as data pre- processing. First level analysis used general linear model (GLM) and each trial type was modelled as one regressor in addition to the six head movement regressors. Four key contrast were carried out to examine the cognitive process of interest: saccade target remapping & change-of-plan processes.
Results showed that the right superior parietal, temporal and hippocampus regions were involved in saccade target remapping. Left lateral prefrontal, left pre-motor region, right ventromedial frontal cortex, right frontal eye fields and bilateral parietal eye fields were involved in saccade target decision processes. Behavioural results supported the view that second saccades could be partially preprogrammed, in parallel with the first step, regardless if a change-of-plan was required or not.
Conclusions:
In conclusion, the findings support the role of the superior parietal region in the saccade target remapping process while the hippocampus area may be involved as a temporal storage to store the original vectors required for the spatial remapping process. The saccade target decision process required a network of both prefrontal executive function regions and saccade related regions.
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