Sight and blindness in the same person: Gating in the visual system (original) (raw)
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Cerebral Cortex, 2011
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.
Psychophysiology and Imaging of Visual Cortical Functions in the Blind: A Review
Behavioural Neurology, 2008
Imaging, transcranial magnetic stimulation, and psychophysiological recordings of the congenitally blind have confirmed functional activation of the visual cortex but have not extensively explained the functional significance of these activation patterns in detail. This review systematically examines research on the role of the visual cortex in processing spatial and non-visual information, highlighting research on individuals with early and late onset blindness. Here, we concentrate on the methods utilized in studying visual cortical activation in early blind participants, including positron emissions tomography (PET), functional magnetic resonance imaging (fMRI), transcranial magnetic stimulation (TMS), and electrophysiological data, specifically event-related potentials (ERPs). This paper summarizes and discusses findings of these studies. We hypothesize how mechanisms of cortical plasticity are expressed in congenitally in comparison to adventitiously blind and short-term visual...
Electrophysiological assessment of visual function in IDDM patients
Electroencephalography and Clinical Neurophysiology/evoked Potentials Section, 1997
The human visual system is characterized by a set of parallel, hierarchical multistage systems that are specialized to process different types of visual stimuli. There are two major parallel streams: the parvocellular (or ventral) and magnocellular (or dorsal) pathways. The former projects to the inferior temporal cortex for object and color vision, whereas the latter connects to the parietal cortex for motion and spatial vision. Individuals with autism spectrum disorder (ASD) often show inferior global motion perception but superior performance in detailed form (local structure) perception. These unique behaviors suggest the possibility of an impairment of the parallel visual pathways in ASD. Visual evoked potentials (VEPs) and event-related potentials (ERPs) are non-invasive electrophysiological methods that provide objective information about the function of the visual system. We have recently developed VEPs and ERPs with visual stimuli designed to preferentially stimulate the different levels of each visual pathway. In this review, we introduce the application of VEP and ERP techniques for the assessment of visual perception in ASD. Current data indicate that the atypical visual perception observed in ASD may be caused by the dysfunction of complicated brain networks within the parallel visual pathways, and may contribute to the impaired social communication involved in ASD. Therefore, we conclude that electrophysiological techniques are useful for understanding the pathophysiology of ASD.
Vision Research, 2013
We examined the visual and cognitive functions of a 72-year-old subject, KP, who recovered his sight after 53 years of visual deprivation. We used visual evoked potentials (VEPs) to pattern-reversal and motion-onset stimuli and cognitive responses (ERPs) during the oddball paradigm to assess the effect of long-term deprivation on a mature visual system. KP lost his sight at the age of 17 years, and light projection onto his right retina was restored at 71 years by a corneal implant. Nine months after sight recovery we recorded reproducible responses to all examined stimuli. The response to pattern reversal contained two P100-like peaks with the later peak being dominant and significantly delayed (260 ms) when compared to the P100s of two control subjects, to whom the stimuli were adjusted in size and contrast to mimic KP's vision. KP's motion-onset VEPs to full-field and peripheral stimuli had a characteristic shape with a well-defined N2 peak; however, both peaks were significantly delayed (262 and 272 ms) compared to control responses. Unlike the P100 and N2 peaks, which represent sensory detection, the P3b/P300 component of the ERP to a target event in the oddball paradigm was not further delayed. In spite of degraded vision and sensory deprivation lasting 53 years, KP displayed reproducible responses to all reported stimuli. Long-term visual deprivation and retinal detachment degraded KP's visual sensory processing, assessed by pattern-reversal and motion-onset VEPs, whereas the cognitive processing of appropriate visual stimuli was not compromised.
Visual Hallucinations in Recovery From Cortical Blindness
Archives of Neurology, 2000
To investigate the cerebral metabolic and functional patterns during recovery from cortical blindness. Design: Follow-up study with serial clinical, metabolic, and functional imaging and visual evoked potentials. Case Presentation: A 24-year-old woman suffered from cortical blindness after cardiac arrest and recovered over a 6-month period. During recovery, she experienced complex visual hallucinations that could be initiated by visual imagery.
NeuroImage, 2011
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy The relationship between the visual evoked potential and the gamma band investigated by blind and semi-blind methods
The Nature of Consciousness in the Visually Deprived Brain
Frontiers in Psychology, 2011
Vision plays a central role in how we represent and interact with the world around us. The primacy of vision is structurally imbedded in cortical organization as about one-third of the cortical surface in primates is involved in visual processes. Consequently, the loss of vision, either at birth or later in life, affects brain organization and the way the world is perceived and acted upon. In this paper, we address a number of issues on the nature of consciousness in people deprived of vision. Do brains from sighted and blind individuals differ, and how? How does the brain of someone who has never had any visual perception form an image of the external world? What is the subjective correlate of activity in the visual cortex of a subject who has never seen in life? More in general, what can we learn about the functional development of the human brain in physiological conditions by studying blindness? We discuss findings from animal research as well from recent psychophysical and functional brain imaging studies in sighted and blind individuals that shed some new light on the answers to these questions.