Popülasyon alıcı bölgeler modeli ile görsel korteks haritalandırılması: İMRG ve uyaran parametrelerinin ayarlanması ve alıcı bölge büyüklüğü incelemeleri

Human visual cortex has been studied extensively since blood oxygen-level dependent (BOLD) signal was discovered by magnetic resonance imaging (MRI) researchers in 1990's (Ogawa et al., 1990). It was not long after that, the researchers achieved to map human visual cortex with functional MRI (Sereno et al., 1995; Deyoe et al., 1996; Engel et al., 1997). In recent past, population receptive field (pRF) method was proposed by Dumoulin and Wandell for receptive field mapping (Dumoulin et al., 2008). Compared to phase-encoded methods, their model added a size parameter to receptive fields, referring to the extent of visual field region processed by neuronal populations. fMRI sequences from Human Connectome Project (Moeller et al., 2018) that used accelerated imaging to scan the whole brain of subjects at ultra-high resolutions were adapted to conduct retinotopy experiments in our institute, National Magnetic Resonance Center, Ankara. pRF maps estimated with three types of stimuli were compared. A local pRF estimation method was tested for a specific region on visual field to achieve greater detail in pRF maps. Subject specific hemodynamic response function (HRF) was estimated in a separate experiment to enhance the pRF estimation analysis. Moreover, pRF size differences were compared between stimuli, hemispheres, and visual processing streams. The results implied that stimulation by natural images yields reliable maps in higher level visual regions, and therefore was selected as the best stimulation protocol. In addition, a guideline has been prepared for vision researchers to conduct pRF analysis.