The Nature article by Shahar Arzy (in Olaf Blanke’s lab) about the young woman who “felt a presence” after stimulation of the brain has made the rounds, with great discussions of the work elsewhere (“Ghost Stories” at The Frontal Cortex, “Ghost in the Machine” at The Island of Doubt) and recently at the new blog Alpha Psy. James over at the Island of Doubt connects this work to developments in neurotheology and the search for spiritual unity with some sort of god presence. Vaughn at Mindhacks has reviewed the article, too, and posted links to Blanke’s other work. The focus over at Mindhacks is the role of the temporal parietal junction (TPJ) in these delusions with an insightful question about the negative emotional content of “the other” in this patient. The upshot is that Arzy and colleagues’ research is fascinating on many levels, and provides a window into ways the self and body are bound, and how that unity unravels with brain damage or psychiatric disturbance.
My interest in the article is slightly different.
To begin though, there’s no doubt that the TPJ is part of a network of areas responsible for the creation and maintenance of activity pertinent to the unity of space, knowledge of the extent of our body and perspective-taking manipulations. Blanke, who coauthored the Nature study, reported work with a similar patient in 2002 in which right angular gyrus stimulation produced out of body experiences and/or autoscopy.
Blanke has also presented work (2005, J. of Neuroscience) in which ERPs are recorded during perspective-taking tasks. The locus of activity in these tasks is the right TPJ, and the onset of activity is within a half second of stimulus presentation. When processing of the right TPJ is interfered with by discharging a strong magnetic field at the surface of the skull (transcranial magnetic stimulation) at the time of peak activity in the perspective-taking tasks, performance on those tasks declined, but performance did not suffer when manipulating representations of objects that aren’t bodies. The right TPJ is body-specific in the representations it can maintain and manipulate.
For me, there are two points that emerge from reading the Nature article. One is that there’s a discrepancy in hemispheric location. In the 2005 article’s neurologically intact participants, the site of all the maintenance work was the right TPJ, but for the “Ghost” woman in the recent report the site of stimulation leading to the phenomenological experience is left-sided. I suggest that the difference lies in functional reorganization of the brain in response to the patient’s epilepsy. Her site of body maintenance may have been “rewritten” to the homologous area. Such plasticity in functional reorganization during epilepsy is well known, not just for linguistic functions (see here also) but for a variety of tasks.
Note that the problem of potential functional reorganization was, similarly, not mentioned in an earlier article I’ve discussed here on self-face reconition processes.
Finally, the really nifty stuff in the Nature article lies in the stimulation details. When this woman’s left TPJ was stimulated with 10 mA of current, she felt the presence behind her. Stimulation of 10-11 mA resulted in a more elaborate report: ”He is behind me, almost at my body, but I do not feel it.” When the patient was instructed to wrap her arms around her legs and embrace her knees and stimulation of 11 mA was delivered, the patient reported an unpleasant sensation of the “man” clasping her in his arms.
If find this revelation of a continuum from extrapersonal space to peripersonal space to a veridical somatic representation, coded within a very small neural area and subject to “warping” by an electrical manipulation, to be proof positive of the fundamentally fragile yet exquistely organized nature of our self-perception.
This article really makes me feel oogie. But in a good way.