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Interaction of ELF Magnetic Fields with Living Matter
Published in Charles Polk, Elliot Postow, CRC Handbook of Biological Effects of Electromagnetic Fields, 2019
Among the various interactions of time-varying ELF fields with living tissues, perhaps the most widely known and well-documented effect is the production of visual sensations known as "phosphates". In the broadest sense, the term "phosphene", which is derived from the Greek words "phos" (light) and "phainein" (to show), means the production of luminous sensations in the eye by agents other than light. These physical agents include mechanical pressure applied directly to the eye and electrical stimulation at ELF frequencies applied to the body surface in the region of the head through contact electrodes. In 1896 d'Arsonval first reported that phosphenes could also be produced by placing the head in an external magnetic field oscillating in the ELF frequency range,13
Transcranial Magnetic and Electric Stimulation
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
Shoogo Ueno, Masaki Sekino, Tsukasa Shigemitsu
The ICNIRP published guideline for limiting exposure to time-varying electric and magnetic field in the frequencies range between 1 Hz and 100 kHz (see Tables 2–4 in ICNIRP 2010, 2014). This guideline has two separate guidances for occupational exposure and for the public. Occupational exposure refers to healthy adults exposed to time-varying electric and magnetic fields from 1 Hz to 10 MHz at their workplaces. This guideline was based on established evidence of the acute effects for protection from the nervous system effects. The then established adverse effects include perception of surface electric charge, direct stimulation of nerve and muscle tissues and induction of retinal phosphenes. Based on the ICNIRP guidelines, the European Parliament introduced its Directive.
Current Approaches, Challenges, and Outlook
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Luke Theogarajan, John Wyatt, Joseph Rizzo
As explained in the preceding sections, the goal of an artificial retinal prosthesis is to stimulate the remaining healthy layers of retinal neurons using brief biphasic pulses of current. These current pulses produce a sensation of vision in the brain that is termed a phosphene. We hope that over time the patient will be able to integrate these phosphenes into useful vision. A key step toward this goal is the development of a chronic implant. Our design philosophy is based on the following requirements: (1) the implant must be powered via an external source (i.e., no batteries); (2) an ability to communicate wirelessly with the implant via external commands; (3) allowing for parameter tuning, that is, current amplitude, duration, and interpulse timing. The first and second constraints were met by using an inductively coupled power and data link. The third was enabled by implementing a flexible stimulator chip architecture as discussed in Section 9.3.1.
Beyond the neural correlates of consciousness: using brain stimulation to elucidate causal mechanisms underlying conscious states and contents
Published in Journal of the Royal Society of New Zealand, 2021
Corinne A. Bareham, Matt Oxner, Tim Gastrell, David Carmel
Stimulation of visual cortex is known to trigger phosphenes, brief visual sensations that do not correspond to any visual input (Marg and Rudiak 1994). Above a certain threshold strength, single TMS pulses to early visual cortex evoke stationery phosphenes, whereas pulses to the part of retinotopic cortex that processes motion, area V5 (which is located laterally to early visual cortex), evoke moving phosphenes. Moving phosphenes are abolished, though, when a supra-threshold V5 pulse is followed 20-40 ms later by a sub-threshold pulse to early visual cortex (Pascual-Leone and Walsh 2001), and a moving phosphene is evoked when a sub-threshold pulse to V5 is followed by a supra-threshold pulse to early visual cortex (Silvanto et al. 2005). These manipulations of the relative timing of paired TMS pulses reveal that conscious experiences may depend on feedback projections to early visual cortex.
Journey of Visual Prosthesis with Progressive Development of Electrode Design Techniques and Experience with CMOS Image Sensors: A Review
Published in IETE Journal of Research, 2018
The development of useful visual prosthesis is based on the psychophysics of phosphenes and specially the interaction between the multiple phosphenes. The Utah electrode array (UEA) proved to be better than the other electrode implants in terms of threshold current, biocompatibility and safe installation in visual cortex [70].
Visual cortical prosthesis: an electrical perspective
Published in Journal of Medical Engineering & Technology, 2021
Léo Pio-Lopez, Romanos Poulkouras, Damien Depannemaecker
From the 1990s, the field see the development of the visual cortical prosthesis with intracortical electrodes. Schmidt et al. showed that a phosphene can be induced by electrical stimulation of the visual cortex with microelectrodes penetrating the cortex. This second line of research is now more predominantly followed [9–11].