What happens when you inject the brains of spirit mediums with radioactive tracers, and then watch their brains? Apparently, you see odd changes in brain behaviour. That's what happened when researchers took ten Brazilian mediums - half experienced, half not - and tracked their brain activity (or at least, regional cerebral blood flow [rCBF], which is closely correlated) using SPECT (Single Photon Emission Computed Tomography).
The researchers firstly did a control experiment, in which the mediums just did some normal writing, and then followed up with another scan while they were practicing 'psychography' - in which spirits allegedly write "through the medium's hand” while they are in a trance.
The finding that surprised the researchers was that the experienced mediums showed higher complexity in their writing while in the trance state, rather than in their control - and yet there was much less activity in the frontal and temporal lobes, the parts of the brain associated with reasoning, planning, generating language...that is, exactly where they should have had more activity for more complex writing.
During psychography, all mediums reported altered states of consciousness, but to different degrees. Experienced mediums spoke of a deeper trance, with clouded consciousness, often reporting being out of the body, and having little or no awareness of the content of what they were writing. Less expert mediums were in a less pronounced trance state and usually reported writing phrases being dictated to them in their minds.
...Subjects attributed their trance writing to “spirits”. Compared to normal writing, less expert mediums showed more activation in the same cognitive-processing areas during psychography, whereas experienced mediums showed a significantly lower level of activation. The less expert ones had to “work harder”, as shown by their relatively higher levels of activation of the cognitive processing area during psychography. Experienced mediums showed significantly reduced rCBF changes during psychography, which is consistent with the notion of automatic (non-conscious) writing and their claims that an “outer source” was planning the written content. Brain regions known to be involved in planning writing were activated less, even though the content was more elaborate than their non-trance writing. These findings are not consistent with faking or role-playing, both of which have been offered as explanations for psychography... studies of cognitive-processing regions involved in reasoning and planning written content showed decreased activity in the experienced mediums, who reported that they were not conscious of psychographed content and had no control over it.
...As the first step toward understanding the neural mechanisms involved in non-pathological dissociation, we emphasize that this finding deserves further investigation both in terms of replication and explanatory hypotheses.