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Christopher Tyler, Lora Likova, Spero Nicholas; Direction specific signals for saccadic eye movements: Effects of traumatic brain injury . Journal of Vision 2014;14(10):1218. doi: 10.1167/14.10.1218.
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Introduction. Although the frontal eye field (FEF) regions of monkey cortex exhibit direction-specific coding contralateral to saccade direction, the same differentiation is not found with fMRI measures in humans. There is weak (~20%) direction specificity for memory-guided saccades and for the direction of attention, but none has been reported for visually-guided saccades. Methods. We have introduced a stepwise (ziggurat) paradigm of 10 leftward saccades followed by 10 rightward saccades to provide sufficient periods of unidirectional saccades in a block-design protocol on a 3T Siemens scanner. The study was conducted in a group of individuals with a history of diffuse traumatic brain injury (with loss of consciousness but no focal brain damage, dTBI) and a group of age-matched controls. Results. Outside occipital cortex (where direction specificity is expected due to the directional visual stimulation), A restricted locus of bihemispheric direction specificity was seen in the region of the precentral gyrus (Brodmann 4) often designated as the human homolog of the FEF, together with the saccadic region of the superior parietal lobule (SPL). The dTBI group showed significantly reduced signals in the FEF, but undiminished direction-specific activation in in the occipital cortex regions and in the SPL (providing assurance that the reductions were specific to the motor activation regions). Conclusion. The main centers for direction-specific saccadic activation were in focal FEF, SPL and occipital cortex. These activations may be interpreted as reflecting, respectively, the initiation of directional control signals, the spatial representation of the direction target and the visual consequences of the eye movements. The direction-specific region of FEF was the main cortical area adversely affected by dTBI.
Meeting abstract presented at VSS 2014
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