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Journal articles on the topic 'Phosphenes'

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Author: Grafiati

Published: 4 June 2021

Last updated: 11 March 2023

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1

Et.al, Manami, K. "Investigation of Electrical Interference towards Phosphene-Based Walking Support System." Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, no. 3 (April 10, 2021): 2178–83. http://dx.doi.org/10.17762/turcomat.v12i3.1164.

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A walking support system with phosphenes for blind people has been investigated. Phosphene is a phenomenon where a flash of light is recognized in the brain by giving an electrical stimulus to human’s visual pathway. Phosphenes can be perceived even if their eyes are closed or they are blind. It has been clarified that phosphenes can be induced to several directions if electrodes placements are precisely selected. When phosphenes are presented to two directions for recognizing two obstacles, two pairs of electrodes must be applied. In such a case, however, the electrical interference occurs due to the short distance between electrodes. In the practical use of the phosphene-based walking support system, the avoidance of electrical interference is significant in order to present the phosphenes precisely. Therefore, in this paper, we first practically investigate the electrical interference by considering the difference in phosphene induction generated by a single pair of electrodes and by two pairs of electrodes. Then, the solutions to avoid the electrical interference are discussed.

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2

Kvašňák, E., M. Orendáčová, and J. Vránová. "Phosphene Attributes Depend on Frequency and Intensity of Retinal tACS." Physiological Research 71, no. 4 (August 31, 2022): 561–71. http://dx.doi.org/10.33549/physiolres.934887.

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Phosphene is the experience of light without natural visual stimulation. It can be induced by electrical stimulation of the retina, optic nerve or cortex. Induction of phosphenes can be potentially used in assistive devices for the blind. Analysis of phosphene might be beneficial for practical reasons such as adjustment of transcranial alternating current stimulation (tACS) frequency and intensity to eliminate phosphene perception (e.g., tACS studies using verum tACS group and sham group) or, on the contrary, to maximize perception of phosphenes in order to be more able to study their dynamics. In this study, subjective reports of 50 healthy subjects exposed to different intensities of retinal tACS at 4 different frequencies (6, 10, 20 and 40 Hz) were analyzed. The effectiveness of different tACS frequencies in inducing phosphenes was at least 92 %. Subject reported 41 different phosphene types; the most common were light flashes and light circles. Changing the intensity of stimulation often induced a change in phosphene attributes. Up to nine phosphene attributes changed when the tACS intensity was changed. Significant positive correlation was observed between number of a different phosphene types and tACS frequency. Based on these findings, it can be concluded that tACS is effective in eliciting phosphenes whose type and attributes change depending on the frequency and intensity of tACS. The presented results open new questions for future research.

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Niketeghad, Soroush, Abirami Muralidharan, Uday Patel, Jessy D. Dorn, Laura Bonelli, Robert J. Greenberg, and Nader Pouratian. "Phosphene perceptions and safety of chronic visual cortex stimulation in a blind subject." Journal of Neurosurgery 132, no. 6 (June 2020): 2000–2007. http://dx.doi.org/10.3171/2019.3.jns182774.

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Stimulation of primary visual cortices has the potential to restore some degree of vision to blind individuals. Developing safe and reliable visual cortical prostheses requires assessment of the long-term stability, feasibility, and safety of generating stimulation-evoked perceptions.A NeuroPace responsive neurostimulation system was implanted in a blind individual with an 8-year history of bare light perception, and stimulation-evoked phosphenes were evaluated over 19 months (41 test sessions). Electrical stimulation was delivered via two four-contact subdural electrode strips implanted over the right medial occipital cortex. Current and charge thresholds for eliciting visual perception (phosphenes) were measured, as were the shape, size, location, and intensity of the phosphenes. Adverse events were also assessed.Stimulation of all contacts resulted in phosphene perception. Phosphenes appeared completely or partially in the left hemifield. Stimulation of the electrodes below the calcarine sulcus elicited phosphenes in the superior hemifield and vice versa. Changing the stimulation parameters of frequency, pulse width, and burst duration affected current thresholds for eliciting phosphenes, and increasing the amplitude or frequency of stimulation resulted in brighter perceptions. While stimulation thresholds decreased between an average of 5% and 12% after 19 months, spatial mapping of phosphenes remained consistent over time. Although no serious adverse events were observed, the subject experienced mild headaches and dizziness in three instances, symptoms that did not persist for more than a few hours and for which no clinical intervention was required.Using an off-the-shelf neurostimulator, the authors were able to reliably generate phosphenes in different areas of the visual field over 19 months with no serious adverse events, providing preliminary proof of feasibility and safety to proceed with visual epicortical prosthetic clinical trials. Moreover, they systematically explored the relationship between stimulation parameters and phosphene thresholds and discovered the direct relation of perception thresholds based on primary visual cortex (V1) neuronal population excitation thresholds.

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Indahlastari, Aprinda, Aditya K. Kasinadhuni, Christopher Saar, Kevin Castellano, Bakir Mousa, Munish Chauhan, Thomas H. Mareci, and Rosalind J. Sadleir. "Methods to Compare Predicted and Observed Phosphene Experience in tACS Subjects." Neural Plasticity 2018 (December 6, 2018): 1–10. http://dx.doi.org/10.1155/2018/8525706.

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Background. Phosphene generation is an objective physical measure of potential transcranial alternating current stimulation (tACS) biological side effects. Interpretations from phosphene analysis can serve as a first step in understanding underlying mechanisms of tACS in healthy human subjects and assist validation of computational models. Objective/Hypothesis. This preliminary study introduces and tests methods to analyze predicted phosphene occurrence using computational head models constructed from tACS recipients against verbal testimonies of phosphene sensations. Predicted current densities in the eyes and the occipital lobe were also verified against previously published threshold values for phosphenes. Methods. Six healthy subjects underwent 10 Hz tACS while being imaged in an MRI scanner. Two different electrode montages, T7-T8 and Fpz-Oz, were used. Subject ratings of phosphene experience were collected during tACS and compared against current density distributions predicted in eye and occipital lobe regions of interest (ROIs) determined for each subject. Calculated median current densities in each ROI were compared to minimum thresholds for phosphene generation. Main Results. All subjects reported phosphenes, and predicted median current densities in ROIs exceeded minimum thresholds for phosphenes found in the literature. Higher current densities in the eyes were consistently associated with decreased phosphene generation for the Fpz-Oz montage. There was an overall positive association between phosphene perceptions and current densities in the occipital lobe. Conclusions. These methods may have promise for predicting phosphene generation using data collected during in-scanner tACS sessions and may enable better understanding of phosphene origin. Additional empirical data in a larger cohort is required to fully test the robustness of the proposed methods. Future studies should include additional montages that could dissociate retinal and occipital stimulation.

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5

Császár, Noémi, Felix Scholkmann, Vahid Salari, Henrik Szőke, and István Bókkon. "Phosphene perception is due to the ultra-weak photon emission produced in various parts of the visual system: glutamate in the focus." Reviews in the Neurosciences 27, no. 3 (April 1, 2016): 291–99. http://dx.doi.org/10.1515/revneuro-2015-0039.

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AbstractPhosphenes are experienced sensations of light, when there is no light causing them. The physiological processes underlying this phenomenon are still not well understood. Previously, we proposed a novel biopsychophysical approach concerning the cause of phosphenes based on the assumption that cellular endogenous ultra-weak photon emission (UPE) is the biophysical cause leading to the sensation of phosphenes. Briefly summarized, the visual sensation of light (phosphenes) is likely to be due to the inherent perception of UPE of cells in the visual system. If the intensity of spontaneous or induced photon emission of cells in the visual system exceeds a distinct threshold, it is hypothesized that it can become a conscious light sensation. Discussing several new and previous experiments, we point out that the UPE theory of phosphenes should be really considered as a scientifically appropriate and provable mechanism to explain the physiological basis of phosphenes. In the present paper, we also present our idea that some experiments may support that the cortical phosphene lights are due to the glutamate-related excess UPE in the occipital cortex.

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Gebrehiwot, Adonay N., Tatsuya Kato, and Kimitaka Nakazawa. "Inducing lateralized phosphenes over the occipital lobe using transcranial magnetic stimulation to navigate a virtual environment." PLOS ONE 16, no. 4 (April 14, 2021): e0249996. http://dx.doi.org/10.1371/journal.pone.0249996.

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Electrical stimulation involving visual areas of the brain produces artificial light percepts called phosphenes. These visual percepts have been extensively investigated in previous studies involving intracortical microsimulation (ICMS) and serve as the basis for developing a visual prosthesis for the blind. Although advances have been achieved, many challenges still remain with implementing a functional ICMS for visual rehabilitation purposes. Transcranial magnetic stimulation (TMS) over the primary occipital lobe offers an alternative method to produce phosphenes non-invasively. A main challenge facing blind individuals involves navigation. Within the scientific community, methods to evaluate the ability of a visual prosthesis to facilitate in navigation has been neglected. In this study, we investigate the effectiveness of evoking lateralized phosphenes to navigate a computer simulated virtual environment. More importantly, we demonstrate how virtual environments along with the development of a visual prosthesis share a mutual relationship benefiting both patients and researchers. Using two TMS devices, a pair of 40mm figure-of-eight coils were placed over each occipital hemisphere resulting in lateralized phosphene perception. Participants were tasked with making a series of left and right turns using peripheral devices depending on the visual hemifield in which a phosphene is present. If a participant was able to accurately perceive all ten phosphenes, the simulated target is able to advance and fully exit the virtual environment. Our findings demonstrate that participants can interpret lateralized phosphenes while highlighting the integration of computer based virtual environments to evaluate the capability of a visual prosthesis during navigation.

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7

Kanamaru, Manami, Phan Xuan Tan, and Eiji Kamioka. "Simulation-Based Designing of Suitable Stimulation Factors for Presenting Two Phosphenes Simultaneously to Lower Side of Field of View." Bioengineering 9, no. 12 (December 2, 2022): 752. http://dx.doi.org/10.3390/bioengineering9120752.

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Using a phosphene has been discussed as a means of informing the visually impaired of the position of an obstacle. Obstacles underfoot have a risk, so it is necessary to inform the visually impaired. A previous study clarified a method of presenting phosphene in three directions in the lower vision; however, the simultaneous presentation of these phosphenes has not been discussed. Another study discussing the effect of electrical interference when stimulating the eyeball with multiple electrodes indicated that it is important to select appropriate stimulation factors to avoid this effect. However, when the stimulation electrodes are arranged remarkably close, there is a high possibility that the stimulus factor presented in the previous study will not apply. In this study, a method for simultaneously presenting phosphenes in the lower vision is presented. The electrode arrangements reported in the previous study to present phosphene in the lower field of vision are used, and the difficulty in the simultaneous presentation of multiple phosphenes in the lower vision is the focus. In this paper, the method of designing the stimulation factors is discussed numerically when the electrodes are arranged remarkably close. As a result, it is shown that stimulation factors different from the previous research were appropriate depending on the distance between the electrodes.

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Niketeghad, Soroush, Abirami Muralidharan, Uday Patel, Jessy Dorn, Robert Greenberg, and Nader Pouratian. "150 Effect of Stimulation Parameters on Visual Percepts Elicited by Stimulation of a Visual Cortical Prosthesis for the Blind." Neurosurgery 64, CN_suppl_1 (August 24, 2017): 236. http://dx.doi.org/10.1093/neuros/nyx417.150.

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Abstract INTRODUCTION Stimulation of human visual cortex is known to elicit visual percepts (phosphenes) which makes it a suitable candidate for generating artificial vision for blind. Although there have been a few attempts to build visual cortical prostheses, a greater understanding of the physiology of stimulation is required to generate useful perceptions. This study aims to characterize the phosphenes elicited by a neurostimulation device and explore the effects of stimulation parameters (amplitude, frequency, pulse-width and burst duration) on the quality of these percepts. METHODS A 30-year-old volunteer with an 8-year history of bare light perception secondary to Voght-Koaynagi-Harada Syndrome participated in this study. Two parallel cortical strip leads (each with four contacts) were implanted over the right medial occipital lobe. Phosphene characteristics were assessed postoperatively using subject's drawings of on a touch screen as well as subjective description of the percepts intensity and color. The stimulus parameters for eliciting a well-defined phosphene were obtained by varying the stimulus parameters for each contact at the beginning of each session during the eight months' period of the study. RESULTS >Stimulation of each of the eight contacts elicited phosphenes with a consistent shape and location in the visual field. The stimulus parameters for generating a well-defined phosphene were stable for six contacts and had to be adjusted for two over the period of the study. Increasing the amplitude and frequency resulted in more intense perceptions and the subject indicated seeing colored phosphenes for certain amplitudes. Simultaneous stimulation of multiple contacts was perceived as a summation of percepts elicited by stimulating the contacts individually. Sequential stimulation of two contacts generated two phosphenes and the subject was able to identify them in order. CONCLUSION Visual cortical prostheses are feasible candidates for creating artificial sight due to reproducibility of the perceptions and consistency of the stimulation parameters required to generate basic visual perceptions.

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Kanamaru, Manami, Phan Xuan Tan, and Eiji Kamioka. "Design of Electrode Placement for Presenting Phosphenes in the Lower Visual Field Based on Electric Field Simulation." Applied Sciences 11, no. 22 (November 19, 2021): 10972. http://dx.doi.org/10.3390/app112210972.

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Presenting visual information, called phosphenes, is a critical method for providing information on the position of obstacles for users of walking support tools for the visually impaired. A previous study has established a method for presenting phosphenes to the right, center, and left of the visual field. However, a method for presenting information on the position of obstacles around the feet using phosphenes, which is essential for the visually impaired, has not been clarified. Therefore, in this study, a method for presenting phosphenes in the lower visual field is presented, towards the aim of realizing a safe walking support tool. Electrode placement is proposed in this paper for the presentation of phosphenes to the right, center, and left of the lower visual field based on the electrode placement method used in the previous study, which presents the phosphene in three locations of the visual field. In addition, electric field simulation is performed, focusing on the electric field value on the eyeball surface, in order to observe whether the proposed electrode placement is able to stimulate the intended region. As a result, it is shown that the intended region on the eyeball surface can be stimulated locally with each of the proposed electrode placements.

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Chen, Xing, Feng Wang, Eduardo Fernandez, and Pieter R. Roelfsema. "Shape perception via a high-channel-count neuroprosthesis in monkey visual cortex." Science 370, no. 6521 (December 3, 2020): 1191–96. http://dx.doi.org/10.1126/science.abd7435.

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Blindness affects 40 million people across the world. A neuroprosthesis could one day restore functional vision in the blind. We implanted a 1024-channel prosthesis in areas V1 and V4 of the visual cortex of monkeys and used electrical stimulation to elicit percepts of dots of light (called phosphenes) on hundreds of electrodes, the locations of which matched the receptive fields of the stimulated neurons. Activity in area V4 predicted phosphene percepts that were elicited in V1. We simultaneously stimulated multiple electrodes to impose visible patterns composed of a number of phosphenes. The monkeys immediately recognized them as simple shapes, motions, or letters. These results demonstrate the potential of electrical stimulation to restore functional, life-enhancing vision in the blind.

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Tehovnik, E. J., W. M. Slocum, C. E. Carvey, and P. H. Schiller. "Phosphene Induction and the Generation of Saccadic Eye Movements by Striate Cortex." Journal of Neurophysiology 93, no. 1 (January 2005): 1–19. http://dx.doi.org/10.1152/jn.00736.2004.

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The purpose of this review is to critically examine phosphene induction and saccadic eye movement generation by electrical microstimulation of striate cortex (area V1) in humans and monkeys. The following issues are addressed: 1) Properties of electrical stimulation as they pertain to the activation of V1 elements; 2) the induction of phosphenes in sighted and blind human subjects elicited by electrical stimulation using various stimulation parameters and electrode types; 3) the induction of phosphenes with electrical microstimulation of V1 in monkeys; 4) the generation of saccadic eye movements with electrical microstimulation of V1 in monkeys; and 5) the tasks involved for the development of a cortical visual prosthesis for the blind. In this review it is concluded that electrical microstimulation of area V1 in trained monkeys can be used to accelerate the development of an effective prosthetic device for the blind.

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Aurora, SK, KMA Welch, and F. Al-Sayed. "The Threshold for Phosphenes is Lower in Migraine." Cephalalgia 23, no. 4 (May 2003): 258–63. http://dx.doi.org/10.1046/j.1468-2982.2003.00471.x.

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We have reported a preliminary study confirming hyperexicitability of occipital cortex in migraine with aura (MwA) using transcranial magnetic stimulation (TMS). We have now completed a blinded study to investigate the occipital cortex in MwA and without aura (MwoA) compared with normal controls (NC) using TMS. TMS was performed using the Caldwell MES-10 stimulator. A circular coil 9.5 cm diameter was applied to the occipital scalp (7 cm above the inion). Stimulator intensity was increased in 10% increments until subjects reported visual phenomena or 100% intensity was reached. Stimulation intensity was then fine tuned to determine the threshold at which phosphenes were seen. Fisher's exact t-test and logrank test were used for statistical comparisons. Ten subjects with MwA and MwoA were compared to 10 NC. The difference in the proportion of subjects with phosphene generation was statistically significant (MwA 100%, MwoA 60% and NC 30%) [ P = 0.003]. The difference in threshold levels for phosphenes was also significant for MwA 42.8%, and controls 57.3% [ P = 0.0001]. There is a difference in threshold for excitability of occipital cortex in MwA and MwoA compared to NC. This is a direct neurophysiological correlate for clinical observations, which have inferred hyperexicitability of the occipital cortex in migraineurs.

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Kar, Kohitij, and Bart Krekelberg. "Transcranial electrical stimulation over visual cortex evokes phosphenes with a retinal origin." Journal of Neurophysiology 108, no. 8 (October 15, 2012): 2173–78. http://dx.doi.org/10.1152/jn.00505.2012.

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Transcranial electrical stimulation (tES) is a promising therapeutic tool for a range of neurological diseases. Understanding how the small currents used in tES spread across the scalp and penetrate the brain will be important for the rational design of tES therapies. Alternating currents applied transcranially above visual cortex induce the perception of flashes of light (phosphenes). This makes the visual system a useful model to study tES. One hypothesis is that tES generates phosphenes by direct stimulation of the cortex underneath the transcranial electrode. Here, we provide evidence for the alternative hypothesis that phosphenes are generated in the retina by current spread from the occipital electrode. Building on the existing literature, we first confirm that phosphenes are induced at lower currents when electrodes are placed farther away from visual cortex and closer to the eye. Second, we explain the temporal frequency tuning of phosphenes based on the well-known response properties of primate retinal ganglion cells. Third, we show that there is no difference in the time it takes to evoke phosphenes in the retina or by stimulation above visual cortex. Together, these findings suggest that phosphenes induced by tES over visual cortex originate in the retina. From this, we infer that tES currents spread well beyond the area of stimulation and are unlikely to lead to focal neural activation. Novel stimulation protocols that optimize current distributions are needed to overcome these limitations of tES.

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Avraham, David, and Yitzhak Yitzhaky. "Effects of Depth-Based Object Isolation in Simulated Retinal Prosthetic Vision." Symmetry 13, no. 10 (September 22, 2021): 1763. http://dx.doi.org/10.3390/sym13101763.

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Visual retinal prostheses aim to restore vision for blind individuals who suffer from outer retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration. Perception through retinal prostheses is very limited, but it can be improved by applying object isolation. We used an object isolation algorithm based on integral imaging to isolate objects of interest according to their depth from the camera and applied image processing manipulation to the isolated-object images. Subsequently, we applied a spatial prosthetic vision simulation that converted the isolated-object images to phosphene images. We compared the phosphene images for two types of input images, the original image (before applying object isolation), and the isolated-object image to illustrate the effects of object isolation on simulated prosthetic vision without and with multiple spatial variations of phosphenes, such as size and shape variations, spatial shifts, and dropout rate. The results show an improvement in the perceived shape, contrast, and dynamic range (number of gray levels) of objects in the phosphene image.

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Nissi, Janita, and Ilkka Laakso. "Magneto- and electrophosphene thresholds in the retina: a dosimetry modeling study." Physics in Medicine & Biology 67, no. 1 (January 7, 2022): 015001. http://dx.doi.org/10.1088/1361-6560/ac46df.

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Abstract Objective. Sensations of flickering light produced by time-varying magnetic fields or electric currents are called magneto- or electrophosphenes. Phosphene thresholds have been used in international guidelines and standards as an estimate of the thresholds of exposure that produce effects in the central nervous system (CNS). However, the estimated threshold values have a large range of uncertainty. Approach. Phosphene thresholds were approximated by simulating five phosphene threshold experiments. Retinal electric fields and currents induced by electric and magnetic stimulation were calculated using the finite element method and 14 anatomically realistic computational models of human heads. Main results. The radial component of retinal current density was determined to be in the range of 6.0–20.6 mA m−2. This study produces more accurate estimates for threshold current density in the retina using detailed anatomical models and the estimates had a reduced range of uncertainty compared to earlier studies. Significance. The results are useful for studying the mechanisms of retinal phosphenes and for the development of exposure limits for the CNS.

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Kaido, Takanobu, Tohru Hoshida, Toshiaki Taoka, and Toshisuke Sakaki. "Retinotopy with coordinates of lateral occipital cortex in humans." Journal of Neurosurgery 101, no. 1 (July 2004): 114–18. http://dx.doi.org/10.3171/jns.2004.101.1.0114.

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Object. The lateral occipital cortex in humans is known as the “extrastriate visual cortex.” It is, however, an unexplored field of research, and the anatomical nomenclature for its surface has still not been standardized. This study was designed to investigate whether the lateral occipital cortex in humans has retinotopic representation. Methods. Four right-handed patients with a diagnosis of intractable epilepsy from space-occupying lesions in the occipital lobe or epilepsy originating in the occipital lobe received permanently implanted subdural electrodes. Electrical cortical stimulation was applied directly applied to the brain through metal electrodes by using a biphasic stimulator. The location of each electrode was measured on a lateral skull x-ray study. Each patient considered a whiteboard with vertical and horizontal median lines. The patient was asked to look at the midpoint on the whiteboard. If a visual hallucination or illusion occurred, the patient recorded its outline, shape, color, location, and motion on white paper one tenth the size of, and with vertical and horizontal median lines similar to those on, the whiteboard. Polar angles and eccentricities of the midpoints of the phosphenes from the coordinate origin were measured on the paper. On stimulation of the lateral occipital lobe, 44 phosphenes occurred. All phosphenes were circular or dotted, with a diameter of approximately 1 cm, except one that was like a curtain in the peripheral end of the upper and lower visual fields on stimulation of the parietooccipital region. All phosphenes appeared in the visual field contralateral to the cerebral hemisphere stimulated. On stimulation of the lateral occipital lobe, 22 phosphenes moved centrifugally or toward a horizontal line. From three-dimensional scatterplots and contour maps of the polar angles and eccentricities in relation to the x-ray coordinates of the electrodes, one can infer that the lateral occipital cortex in humans has retinotopic representation. Conclusions. The authors found that phosphenes induced by electrical cortical stimulation of the lateral occipital cortex represent retinotopy. From these results one can assert that visual field representation with retinotopic relation exists in the extrastriate visual cortex.

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Bohotin, V., A. Fumai, M. Vandenheede, C. Bohotin, and J. Schoenen. "Excitability of Visual V1-V2 and Motor Cortices To Single Transcranial Magnetic Stimuli in Migraine: A Reappraisal Using A Figure-Of-Eight Coil." Cephalalgia 23, no. 4 (May 2003): 264–70. http://dx.doi.org/10.1046/j.1468-2982.2003.00475.x.

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We used transcranial magnetic stimulation (TMS) with a figure-of-eight coil to excite motor and visual V1-V2 cortices in patients suffering from migraine without (MO) ( n = 24) or with aura (MA) ( n = 13) and in healthy volunteers (HV) ( n = 33). Patients who had a migraine attack within 3 days before or after the recordings were excluded. All females were recorded at mid-cycle. Single TMS pulses over the occipital cortex elicited phosphenes in 64% of HV, 63% of MO and 69% of MA patients. Compared with HV, the phosphene threshold was significantly increased in MO ( P = 0.001) and in MA ( P = 0.007), but there was no difference between the two groups of migraineurs. The motor threshold tended to be higher in both migraine groups than in HV, but the differences were not significant. In conclusion, this study shows that two-thirds (64.86%) of patients affected by either migraine type present an increased phosphene threshold in the interictal period, which suggests that their visual cortex is hypoexcitable.

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Sarıhan, Işık. "Double Vision, Phosphenes and Afterimages." European journal of analytic philosophy 16, no. 1 (May 21, 2020): 5–32. http://dx.doi.org/10.31820/ejap.16.1.1.

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Pure representationalism or intentionalism for phenomenal experience is the theory that all introspectible qualitative aspects of a conscious experience can be analyzed as qualities that the experience non-conceptually represents the world to have. Some philosophers have argued that experiences such as afterimages, phosphenes and double vision are counterexamples to the representationalist theory, claiming that they are non- representational states or have non-representational aspects, and they are better explained in a qualia-theoretical framework. I argue that these states are fully representational states of a certain kind, which I call “automatically non-endorsed representations”, experiential states the veridicality of which we are almost never committed to, and which do not trigger explicit belief or disbelief in the mind of the subject. By investigating descriptive accounts of afterimages by two qualia theorists, I speculate that the mistaken claims of some anti-representationalists might be rooted in confusing two senses of the term “seeming”.

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Khan, E., F. Maréchal, R. Dendale, C. Mabit, V. Calugaru, L. Desjardin, and L. Narici. "Anomalous phosphenes in ocular protontherapy." Advances in Space Research 45, no. 7 (April 2010): 846–49. http://dx.doi.org/10.1016/j.asr.2009.11.021.

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Thariat, Juliette, Cecilia Leal, Alessander d'Ascoli, Pauline Jardel, Jean Pierre Caujolle, Joel Herault, Stephanie Baillif, Celia Maschi, and Giorgia Loreti. "Phosphenes in patients receiving radiotherapy." Lancet Oncology 17, no. 7 (July 2016): 869–71. http://dx.doi.org/10.1016/s1470-2045(16)30034-1.

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Convento, Silvia, Chiara Galantini, Nadia Bolognini, and Giuseppe Vallar. "Neuromodulation of crossmodal influences on visual cortex excitability." Seeing and Perceiving 25 (2012): 149. http://dx.doi.org/10.1163/187847612x647810.

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Crossmodal interactions occur not only within brain regions deemed to be heteromodal, but also within primary sensory areas, traditionally considered as modality-specific. So far, mechanisms of crossmodal interactions in primary visual areas remain largely unknown. In the present study, we explored the effect of crossmodal stimuli on phosphene perception, induced by single-pulse transcranial magnetic stimulation (sTMS) delivered to the occipital visual cortex. In three experiments, we showed that redundant auditory and/or tactile information facilitated the detection of phosphenes induced by occipital sTMS, applied at sub-threshold intensity, which also increased their level of brightness, with the maximal enhancement occurring for trimodal stimulus combinations. Such crossmodal enhancement can be further boosted by the brain polarization of heteromodal areas mediating crossmodal links in spatial attention. Specifically, anodal transcranial direct current stimulation (tDCS) of both the occipital and the parietal cortices facilitated phosphene detection under unimodal conditions, whereas anodal tDCS of the parietal and temporal cortices enhanced phosphene detection selectively under crossmodal conditions, when auditory or tactile stimuli were combined with occipital sTMS. Overall, crossmodal interactions can enhance neural excitability within low-level visual areas, and tDCS can be used for boosting such crossmodal influences on visual responses, likely affecting mechanisms of crossmodal spatial attention involving feedback modulation from heteromodal areas on sensory-specific cortices. TDCS can effectively facilitate the integration of multisensory signals originating from the external world, hence improving visual perception.

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Mathis, Thibaud, Stephane Vignot, Cecila Leal, Jean-Pierre Caujolle, Celia Maschi, Martine Mauget-Faÿsse, Laurent Kodjikian, Stéphanie Baillif, Joel Herault, and Juliette Thariat. "Mechanisms of phosphenes in irradiated patients." Oncotarget 8, no. 38 (June 28, 2017): 64579–90. http://dx.doi.org/10.18632/oncotarget.18719.

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Drover, Jonathan D., and G. Bard Ermentrout. "Phase Boundaries as Electrically Induced Phosphenes." SIAM Journal on Applied Dynamical Systems 5, no. 4 (January 2006): 529–51. http://dx.doi.org/10.1137/050646469.

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Oswalt, Denise, William Bosking, Ping Sun, Sameer A. Sheth, Soroush Niketeghad, Michelle Armenta Salas, Uday Patel, et al. "Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects." Brain Stimulation 14, no. 5 (September 2021): 1356–72. http://dx.doi.org/10.1016/j.brs.2021.08.024.

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Fan, Jin, Jing Wang, Qiushi Ren, Yanyu Lu, Ying Zhao, Xinyu Chai, Chunaqing Zhou, and Chen Tao. "Estimating the Position of Simulated Phosphenes Using a Tactile Guide." Seeing and Perceiving 24, no. 2 (2011): 125–40. http://dx.doi.org/10.1163/187847511x570088.

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AbstractA visual prosthesis provides usable visual information to the patient in the form of phosphenes, that is, punctate photic sensations seen after electrical stimulation. Stimulation via different electrodes results in phosphenes in different positions within the visual field. Simulation studies can provide data on the possible limitations of prosthetic stimulation. We used a head mounted screen to monocularly present constant or flickering light spots of different sizes, or luminance to normally sighted subjects. Subjects were asked to judge the location of the spots using a polar coordinate tactile guide; positioning average error and dispersion were analyzed. With the increase of eccentricity, the positioning average error and dispersion were also increased. The performances under large, stable and high luminance conditions were better than that under small, flickering and low luminance conditions, respectively. Repeated training sessions were shown to significantly improve the positioning performance.

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Bhatt, NikunjK, Aniruddha Phadke, SourabhD Patwardhan, and NidhiS Patwardhan. "Ivabradine-induced photosensitivity and phosphenes: Case report." Indian Journal of Ophthalmology - Case Reports 2, no. 1 (2022): 179. http://dx.doi.org/10.4103/ijo.ijo_1606_21.

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Thariat, J. O., G. Loreti, C. Maschi, J. P. Caujolle, and J. Herault. "Phosphenes Under Proton therapy for Eye Tumors." International Journal of Radiation Oncology*Biology*Physics 93, no. 3 (November 2015): E79. http://dx.doi.org/10.1016/j.ijrobp.2015.07.744.

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Dagnino, Bruno, Marie-Alice Gariel-Mathis, and Pieter R. Roelfsema. "Microstimulation of area V4 has little effect on spatial attention and on perception of phosphenes evoked in area V1." Journal of Neurophysiology 113, no. 3 (February 1, 2015): 730–39. http://dx.doi.org/10.1152/jn.00645.2014.

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Previous transcranial magnetic stimulation (TMS) studies suggested that feedback from higher to lower areas of the visual cortex is important for the access of visual information to awareness. However, the influence of cortico-cortical feedback on awareness and the nature of the feedback effects are not yet completely understood. In the present study, we used electrical microstimulation in the visual cortex of monkeys to test the hypothesis that cortico-cortical feedback plays a role in visual awareness. We investigated the interactions between the primary visual cortex (V1) and area V4 by applying microstimulation in both cortical areas at various delays. We report that the monkeys detected the phosphenes produced by V1 microstimulation but subthreshold V4 microstimulation did not influence V1 phosphene detection thresholds. A second experiment examined the influence of V4 microstimulation on the monkeys' ability to detect the dimming of one of three peripheral visual stimuli. Again, microstimulation of a group of V4 neurons failed to modulate the monkeys' perception of a stimulus in their receptive field. We conclude that conditions exist where microstimulation of area V4 has only a limited influence on visual perception.

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Silvanto, Juha, Nilli Lavie, and Vincent Walsh. "Stimulation of the Human Frontal Eye Fields Modulates Sensitivity of Extrastriate Visual Cortex." Journal of Neurophysiology 96, no. 2 (August 2006): 941–45. http://dx.doi.org/10.1152/jn.00015.2006.

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The precise role of frontal eye fields (FEF) in vision independent of their role in eye movements remains a matter of debate. One proposal is that the FEF exert top-down influences on the extrastriate visual cortex prior to eye movement preparation. Here we establish, by use of transcranial magnetic stimulation (TMS), that activity in the human FEFs has a direct effect on the sensitivity of extrastriate visual area MT/V5, and that the spatial organization of this top-down effect is lateralized in the human brain. We show that phosphene threshold—the TMS intensity required to elicit a visual perception—for MT/V5 stimulation changes as a function of the delay between the application of TMS over FEF and MT/V5. The effects were specific to the location and time of stimulation. Stimulation of FEF 20–40 ms prior to stimulation of MT/V5 decreased the intensity of MT/V5 stimulation required to elicit phosphenes: TMS of the right FEF changed the sensitivity of left and right MT/V5 whereas TMS of the left FEF changed the sensitivity only of the left MT/V5. Thus, the sensitivity of human extrastriate cortex is modulated by activity in the FEF.

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Fu, Xingyang, Xinyao Li, and Jiaxi Xu. "Synthesis of β-Phosphinolactams from Phosphenes and Imines." Organic Letters 23, no. 22 (October 28, 2021): 8733–37. http://dx.doi.org/10.1021/acs.orglett.1c03182.

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31

Hodgson. "Shamanism, Phosphenes, and Early Art: An Alternative Synthesis." Current Anthropology 41, no. 5 (2000): 866. http://dx.doi.org/10.2307/3596749.

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Cervetto, L., G. C. Demontis, and C. Gargini. "Cellular mechanisms underlying the pharmacological induction of phosphenes." British Journal of Pharmacology 150, no. 4 (February 2007): 383–90. http://dx.doi.org/10.1038/sj.bjp.0706998.

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33

Chen, Spencer C., Gregg J. Suaning, John W. Morley, and Nigel H. Lovell. "Simulating prosthetic vision: I. Visual models of phosphenes." Vision Research 49, no. 12 (June 2009): 1493–506. http://dx.doi.org/10.1016/j.visres.2009.02.003.

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Wu, D. A., Y. Kamitani, F. Maeda, and S. Shimojo. "Interaction of TMS-induced phosphenes and visual stimuli." Journal of Vision 1, no. 3 (March 14, 2010): 198. http://dx.doi.org/10.1167/1.3.198.

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Meador, K. J., P. G. Ray, and D. W. Loring. "Physiology of perception: parameters of TMS-induced phosphenes." Electroencephalography and Clinical Neurophysiology 102, no. 1 (January 1997): P12. http://dx.doi.org/10.1016/s0013-4694(97)86260-8.

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Hodgson, Derek. "Shamanism, Phosphenes, and Early Art: An Alternative Synthesis." Current Anthropology 41, no. 5 (December 2000): 866–73. http://dx.doi.org/10.1086/317415.

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Grüsser, Otto-Joachim. "Migraine phosphenes and the retino-cortical magnification factor." Vision Research 35, no. 8 (April 1995): 1125–34. http://dx.doi.org/10.1016/0042-6989(94)00187-q.

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38

Taylor, John-Paul, Michael Firbank, Nicola Barnett, Sarah Pearce, Anthea Livingstone, Urs Mosimann, Janet Eyre, Ian G. McKeith, and John T. O'Brien. "Visual hallucinations in dementia with Lewy bodies: transcranial magnetic stimulation study." British Journal of Psychiatry 199, no. 6 (December 2011): 492–500. http://dx.doi.org/10.1192/bjp.bp.110.090373.

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BackgroundThe aetiology of visual hallucinations is poorly understood in dementia with Lewy bodies. Pathological alterations in visual cortical excitability may be one contributory mechanism.AimsTo determine visual cortical excitability in people with dementia with Lewy bodies compared with aged-matched controls and also the relationship between visual cortical excitability and visual hallucinations in dementia with Lewy bodies.MethodVisual cortical excitability was determined by using transcranial magnetic stimulation (TMS) applied to the occiput to elicit phosphenes (transient subjective visual responses) in 21 patients with dementia with Lewy bodies and 19 age-matched controls.ResultsPhosphene parameters were similar between both groups. However, in the patients with dementia with Lewy bodies, TMS measures of visual cortical excitability correlated strongly with the severity of visual hallucinations (P = 0.005). Six patients with dementia with Lewy bodies experienced visual hallucination-like phosphenes (for example, seeing people or figures on stimulation) compared with none of the controls (P = 0.02).ConclusionsIncreased visual cortical excitability in dementia with Lewy bodies does not appear to explain visual hallucinations but it may be a marker for their severity.

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Silva, Andrew E., Katelyn Tsang, Syeda Javeria Hasan, and Benjamin Thompson. "Precise oculocentric mapping of transcranial magnetic stimulation-evoked phosphenes." NeuroReport 32, no. 11 (June 22, 2021): 913–17. http://dx.doi.org/10.1097/wnr.0000000000001683.

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Cowey, Alan, and Vincent Walsh. "Magnetically induced phosphenes in sighted, blind and blindsighted observers." NeuroReport 11, no. 14 (September 2000): 3269–73. http://dx.doi.org/10.1097/00001756-200009280-00044.

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41

Peer, J., and A. Kendl. "Transcranial stimulability of phosphenes by long lightning electromagnetic pulses." Physics Letters A 374, no. 29 (June 2010): 2932–35. http://dx.doi.org/10.1016/j.physleta.2010.05.023.

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Bagattini, Chiara, Chiara Mazzi, and Silvia Savazzi. "Waves of awareness for occipital and parietal phosphenes perception." Neuropsychologia 70 (April 2015): 114–25. http://dx.doi.org/10.1016/j.neuropsychologia.2015.02.021.

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43

Schutter, Dennis J. L. G., and Ruud Hortensius. "Retinal origin of phosphenes to transcranial alternating current stimulation." Clinical Neurophysiology 121, no. 7 (July 2010): 1080–84. http://dx.doi.org/10.1016/j.clinph.2009.10.038.

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Wang, Jing, Rongfeng Zhao, Peitong Li, Zhiqiang Fang, Qianqian Li, Yanling Han, Ruyan Zhou, and Yun Zhang. "Clinical Progress and Optimization of Information Processing in Artificial Visual Prostheses." Sensors 22, no. 17 (August 30, 2022): 6544. http://dx.doi.org/10.3390/s22176544.

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Visual prostheses, used to assist in restoring functional vision to the visually impaired, convert captured external images into corresponding electrical stimulation patterns that are stimulated by implanted microelectrodes to induce phosphenes and eventually visual perception. Detecting and providing useful visual information to the prosthesis wearer under limited artificial vision has been an important concern in the field of visual prosthesis. Along with the development of prosthetic device design and stimulus encoding methods, researchers have explored the possibility of the application of computer vision by simulating visual perception under prosthetic vision. Effective image processing in computer vision is performed to optimize artificial visual information and improve the ability to restore various important visual functions in implant recipients, allowing them to better achieve their daily demands. This paper first reviews the recent clinical implantation of different types of visual prostheses, summarizes the artificial visual perception of implant recipients, and especially focuses on its irregularities, such as dropout and distorted phosphenes. Then, the important aspects of computer vision in the optimization of visual information processing are reviewed, and the possibilities and shortcomings of these solutions are discussed. Ultimately, the development direction and emphasis issues for improving the performance of visual prosthesis devices are summarized.

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Sinclair, Nicholas C., Mohit N. Shivdasani, Thushara Perera, Lisa N. Gillespie, Hugh J. McDermott, Lauren N. Ayton, and Peter J. Blamey. "The Appearance of Phosphenes Elicited Using a Suprachoroidal Retinal Prosthesis." Investigative Opthalmology & Visual Science 57, no. 11 (September 21, 2016): 4948. http://dx.doi.org/10.1167/iovs.15-18991.

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46

Kastner, S., I. Demmer, and U. Ziemann. "P424 Transient scotomas and phosphenes induced by transcranial magnetic stimulation." Electroencephalography and Clinical Neurophysiology 99, no. 4 (October 1996): 374. http://dx.doi.org/10.1016/0013-4694(96)88599-3.

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47

Kim, Ivana K. "Melanocytoma of the Optic Nerve Associated With Sound-Induced Phosphenes." Archives of Ophthalmology 124, no. 2 (February 1, 2006): 273. http://dx.doi.org/10.1001/archopht.124.2.273.

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48

Kapócs, Gábor, Felix Scholkmann, Vahid Salari, Noémi Császár, Henrik Szőke, and István Bókkon. "Possible role of biochemiluminescent photons for lysergic acid diethylamide (LSD)-induced phosphenes and visual hallucinations." Reviews in the Neurosciences 28, no. 1 (January 1, 2017): 77–86. http://dx.doi.org/10.1515/revneuro-2016-0047.

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AbstractToday, there is an increased interest in research on lysergic acid diethylamide (LSD) because it may offer new opportunities in psychotherapy under controlled settings. The more we know about how a drug works in the brain, the more opportunities there will be to exploit it in medicine. Here, based on our previously published papers and investigations, we suggest that LSD-induced visual hallucinations/phosphenes may be due to the transient enhancement of bioluminescent photons in the early retinotopic visual system in blind as well as healthy people.

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Sparing, Roland, Manuel Dafotakis, Dorothee Buelte, Ingo G. Meister, and Johannes Noth. "Excitability of human motor and visual cortex before, during, and after hyperventilation." Journal of Applied Physiology 102, no. 1 (January 2007): 406–11. http://dx.doi.org/10.1152/japplphysiol.00770.2006.

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In humans, hyperventilation (HV) has various effects on systemic physiology and, in particular, on neuronal excitability and synaptic transmission. However, it is far from clear how the effects of HV are mediated at the cortical level. In this study we investigated the effects of HV-induced hypocapnia on primary motor (M1) and visual cortex (V1) excitability. We used 1) motor threshold (MT) and phosphene threshold (PT) and 2) stimulus-response (S-R) curves (i.e., recruitment curves) as measures of excitability. In the motor cortex, we additionally investigated 3) the intrinsic inhibitory and facilitatory neuronal circuits using a short-interval paired-pulse paradigm. Measurements were performed before, during, and after 10 min of HV (resulting in a minimum end-tidal Pco2 of 15 Torr). HV significantly increased motor-evoked potential (MEP) amplitudes, particularly at lower transcranial magnetic stimulation (TMS) intensities. Paired-pulse stimulation indicated that HV decreases intracortical inhibition (ICI) without changing intracortical facilitation. The results suggestthat low Pco2 levels modulate, in particular, the intrinsic neuronal circuits of ICI, which are largely mediated by neurons containing γ-aminobutyric acid. Modulation of MT probably resulted from alterations of Na+ channel conductances. A significant decrease of PT, together with higher intensity of phosphenes at low stimulus intensities, furthermore suggested that HV acts on the excitability of M1 and V1 in a comparable fashion. This finding implies that HV also affects other brain structures besides the corticospinal motor system. The further exploration of these physiological mechanisms may contribute to the understanding of the various HV-related clinical phenomenona.

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Evans, Ian D., Stephen Palmisano, and Rodney J. Croft. "Retinal and Cortical Contributions to Phosphenes During Transcranial Electrical Current Stimulation." Bioelectromagnetics 42, no. 2 (January 13, 2021): 146–58. http://dx.doi.org/10.1002/bem.22317.

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