Neural Correlates of Hysterical Blindness

Abstract

The neural mechanisms underlying conversion disorders such as hysterical blindness are at present unknown. Typically, patients are diagnosed through exclusion of neurological disease and the absence of pathologic neurophysiological diagnostic findings. Here, we investigate the neural basis of this disorder by combining electrophysiological (event-related potentials) and hemodynamic measures (functional magnet resonance tomography) in a patient with hysterical blindness before and after successful treatment. Importantly, the blindness was limited to the left upper and right lower visual quadrant offering the possibility to use the other 2 sighted quadrants as controls. While the functional magnetic resonance imaging activations were normal for visual stimulation electrophysiological indices of visual processing were modulated in a specific manner. Before treatment, the amplitude of the N1 event-related potentials component had smaller amplitudes for stimuli presented in the blind quadrants of the visual field. Following successful treatment the N1 component elicited by stimuli presented in formerly blind quadrants had a normal distribution without any amplitude differences between the 4 quadrants. The current findings point out that dissociative disorders such as hysterical blindness may have neurophysiological correlates. Furthermore, the observed neurophysiological pattern suggests an involvement of attentional mechanisms in the neural basis hysterical blindness.

It is time to combine the two main traditions in the research on the neural correlates of consciousness: C = L × D

“…Artificial stimulation of the intralaminar thalamic sites that are part of the nonspecific system augments visual evoked potentials in response to grating stimuli (Hunsperger and Roman, 1976). Visual, auditory and somatosensory research using recording of brain potentials has repeatedly shown that the level of expression and timing of the negative-polarity potential N1 (with post-stimulus latency equal to about 50–200 ms depending on the modality and stimulation characteristics) strongly correlates with conscious perception (Uttal and Cook, 1964; Wagman and Battersby, 1964; Hassler, 1979; Alter et al, 1990; Cauller and Kulics, 1991; Bachmann, 1994; Imas et al, 2006; Schubert et al, 2006; Schoenfeld et al, 2011; Auksztulewicz et al, 2012; Auksztulewicz and Blankenburg, 2013; Sinke et al, 2014; Pitts et al, submitted). For example, while early post-stimulus potential components are more or less invariant between sleep or sedation on the one hand and awake conditions on the other hand (or even increased in sedation – Imas et al, 2006), N1 is considerably suppressed in the unconscious state.…”

“…When similar monocular textures fuse into subjectively visible images, conspicuous occipitally recorded negative component is present, but absent when fusion into visibility is not achieved (Fahrenfort et al, 2012). Moreover, recently it was shown that whether subjective experience of a visual stimulus in hysterical blindness is present or not is reflected in the amplitude of N1 (Schoenfeld et al, 2011). Importantly, while N1 appeared as an authentic NCC, fMRI recording data could not differentiate between consciously seen vs unseen stimuli.…”

Brain circuits implicated in psychogenic paralysis in conversion disorders and hypnosis

“…A few brain-imaging studies have examined conversion deficits affecting other neurological functions such as somatosensory loss [35,53], visual loss [9,85,109], or memory loss [33,55,98]. In most cases, reduced activity was observed in brain areas involved in the impaired functions, including somatosensory cortices, occipital lobe, or temporal lobe, respectively (for review see [104,105]).…”

The neuropsychological and neurophysiological profile of women with pseudoseizure

“…Although there are only a few studies on the role of biological factors in CD, some recent publications report a possible pathology in the cerebral functions of these patients [4][5][6][7]. These studies have mostly been carried out in the subtype of CD with motor signs and are associated with hemispheric dominance, event-related evoked potentials, structural and functional brain imaging and neuropsychological tests (NPT).…”