Hi people. The (preoperative diagnostic) Wada test in which brain hemispheres are alternately anesthetized while the still-conscious parts of the patient's brain attempt to name and recall presented objects provides strong medical evidence of conscious subsystems. Hemispherectomies, as Luke points out, and even strokes would also seem to be supportive.
But more to the point, the fact that there is a conscious experience of losing neural communication with an entire hemisphere (for example, the realization that one can no longer produce speech or lift one arm) provides, I've argued, good reason to think that the substratum of that experience was conscious prior to the loss. There are alternative interpretations that seem more intuitive at first, but I think they require some serious metaphysical commitments. I have a hemispherectomies 2016 paper on this, and I give a more elaborate defense in my 2021 paper on IIT for anyone who's interested.