Here is a quote that from time to time I need, but I always have to go searching for it. From Greg Smith in the FARMS Review of Books:
“A neuroimaging team might study a patient who reports that he is “seeing” an apple. The team could demonstrate that certain areas in the occipital cortex light up in a predictable pattern whenever the patient reports “seeing” an apple. The skeptics would have us believe that because this reported sensation can be detected on a PET scan, there is no such thing as literal vision and no literal apple! This is counterintuitive at best. Without knowing whether an apple was, in fact, in front of the patient’s open eyes during the scan, there would be no way to tell from the radiology data whether the apple existed or not. For spiritual matters, it is impossible to crack open the scanner and spot the apple (or its absence).
“Put simply, all cognition must cause brain level changes. Everything we think, feel, experience, or sense must induce a change at the level of the neurons. Is it any surprise that similar experiences will provoke similar areas of the brain to behave in similar ways, since we know that the brain is anatomically specialized for a variety of functions? Whether such brain changes are all that is happening is, of course, the intriguing question. Newberg makes this point repeatedly.
“So the key question remains: Are brain changes the “phenomenon” (i.e., the whole of the experience, a “hallucination” of an apple), or are they an “epiphenomenon” (i.e., caused by something outside of the brain: light traveling from an apple, striking the retina, and influencing the neurons)? There’s no way to tell, by this—or any—set of experiments. Newberg argues that the changes wrought by spiritual experiences are every bit as “real” as those from standard sensory phenomena.”