When the control's layout property mode is in vertical scrolling direction, this method scrolls into view the thumbnails contained in the row next to the row in current view. When the control's layout property mode is in horizontal scrolling direction, this method scrolls into view the thumbnails contained in the column next to the column in current view. For thumbnails layout in a grid format, the control always has scroll bar on the right, therefore, the scroll position will move to the next line of thumbnails. When the thumbnail layout has a single vertical column (a special case of grid with one column), the scroll position moves into view one thumbnail below the current position.

Reference

ImGearThumbnailList class
ImGearThumbnailList Members