def applyMainArgs(args, overlayList, displayCtx):
    """Applies top-level arguments that are not specific to the scene or
    any overlays. This should be called before either :func:`applySceneArgs`
    or :func:`applyOverlayArgs`.

    :arg args:        :class:`argparse.Namespace` object containing the parsed
                      command line arguments.

    :arg overlayList: A :class:`.OverlayList` instance.

    :arg displayCtx:  A :class:`.DisplayContext` instance.
    """
    from fsleyes.displaycontext.volumeopts import VolumeOpts
    VolumeOpts.setInitialDisplayRange(args.initialDisplayRange)
    if args.bigmem is not None:
        displayCtx.loadInMemory = args.bigmem
    if args.neuroOrientation is not None:
        displayCtx.radioOrientation = not args.neuroOrientation
    displayCtx.autoDisplay = args.autoDisplay
