Stimulating the aberrant brain: Evidence for increased cortical hyperexcitability from a transcranial direct current stimulation (tDCS) study of individuals predisposed to anomalous perceptions

Abstract

Findings from neurological and clinical groups have shown that increased predisposition to anomalous experience/aura reflects an elevation in aberrant neural processes in the brain. However, studies of anomalous experiences in non-clinical/non-neurological groups are less clear on this matter and are more typically confined to subjective questionnaire measures alone. The current investigation, the first to our knowledge, carried out a transcranial Direct Current Stimulation (tDCS) study of cortical hyperexcitability, and its association with anomalous experience in non-clinical/non-neurological groups. Sixty participants completed; (i) both excitatory (anodal) and inhibitory (cathodal) brain stimulation conditions of the visual cortex; (ii) a computerised pattern-glare task, where observers reported phantom visual distortions from viewing highly irritable visual patterns (a metric of cortical hyperexcitability), and; (iii) questionnaire measures of predisposition to anomalous perceptions. There were no reliable signs of cortical hyperexcitability (via pattern-glare tasks) when collapsed across the whole sample. However, a significant positive correlation between predisposition to anomalous experience and elevated signs of cortical hyperexcitability was observed. Crucially, there was a significant negative correlation between tDCS stimulatory conditions. A visual cortex that reacted more strongly to excitatory stimulation, responded less well to inhibitory suppression, and this pattern was related to predisposition to anomalous perceptions. Both findings are consistent with the presence of a hyperexcitable cortex. Collectively the present findings provide objective evidence that the brains of individuals predisposed to anomalous experiences/hallucinations can be hyperexcitable - even in the non-clinical/non-neurological population. These data are consistent with continuum models of anomalous experience and have important implications for contemporary theories of aberrations in self-consciousness.

Evidence for distinct clusters of diverse anomalous experiences and their selective association with signs of elevated cortical hyperexcitability

“…In addition, the Cronbach's alpha (> .80) suggested that the responses to these items were highly consistent with each otheran observation further bolstered by the near perfect replication of the original study for this factor. Pattern and light induced visual stress symptoms (which can include induced somatic discomforts) are consistent with the notion of elevated hyperexcitability in visual cortex and have been well documented in studies on migraine and non-clinical samples predisposed to aberrant perceptions and hallucinations Braithwaite, Mevorach, & Takahashi., 2015;Harle, Shepherd, & Evans, 2006;Huang et al, 2003;Wilkins, 1995).…”

Altered neural dynamics in people who report spontaneous out of body experiences

“…Further support for this position comes from subsequent work which showed that in a group of clinically healthy student volunteers, participants who experienced increased pattern-glare showed increased response to cortical excitation, delivered via anodal tDCS stimulation and decreased response to cortical inhibition delivered via cathodal stimulation (Braithwaite, Mevorach, & Takahashi, 2015).…”

Practice makes the deficiency of global motion detection in people with pattern-related visual stress more apparent

“…The fact that PRVS is more likely to be evoked under binocular than monocular conditions also supports this view [ 12 ]. Unlike the natural images that cause a sparse response in the visual system, visually averse stimuli may cause an anomalous response as found in PRVS, as a result of either cortical hyperexcitability or poor cortical inhibition [ 5 , 13 – 16 ]. Previous studies suggested an overload in extrastriate dorsal visual pathway in PRVS [ 17 ].…”

“…Moreover, cortical hyperexcitability has also been reported in the visual cortex of the people with migraines [ 28 , 29 ]. Therefore, PRVS and migraine should be viewed as the two ends of a continuum, with PRVS in the non-clinical population who experience abnormal illusions and migraine in the clinical population who suffer migraine attacks [ 16 ].…”