Evidence for elevated cortical hyperexcitability and its association with out-of-body experiences in the non-clinical population: new findings from a pattern-glare task.

Individuals with no history of neurological or psychiatric illness can report hallucinatory Out-of-Body Experiences (OBEs) and display elevated scores on measures of temporal-lobe dysfunction (Braithwaite et al., 2011). However, all previous investigations of such biases in non-clinical populations are based on indirect questionnaire measures. Here we present the first empirical investigation that a non-clinical OBE group is subject to pattern-glare, possibly as a result of cortical hyperexcitability (Wilkins et al., 1984). Fifty-nine students at the University of Birmingham viewed a series of square-wave gratings with spatial frequencies of approximately .7, 3 and 11 cycles-per-degree, both black/white and of contrasting colours. The illusions and discomfort reported when viewing gratings with mid-range spatial frequency have been hypothesized to reflect cortical hyperexcitability (Wilkins, 1995; Huang et al., 2003). Participants also completed the Cardiff Anomalous Perception Scale (CAPS: Bell et al., 2006) which included experiential measures of disruptions in 'Temporal-lobe Experience'. Participants who reported OBEs also reported significantly more visual illusions/distortions and significantly greater discomfort as a result of viewing the mid-frequency gratings. There were no such differences with respect to gratings with relatively lower or higher spatial frequency. The OBE group also produced significantly elevated scores on the CAPS measures of Temporal-lobe Experience, relative to controls. Collectively, the results are consistent with there being a neural 'vulnerability' in the cortices of individuals pre-disposed to some hallucinations, even in the non-clinical population.