Phosphenes and transient scotomas induced by magnetic stimulation of the occipital lobe: their topographic relationship

“Similarly to the motor cortex non-motor areas can also be mapped; for example, one can produce phosphenes in different regions of the visual field with an accuracy of 1–2 degrees of visual angle by stimulating appropriate parts of the occipital cortex (Kammer, 1999; Merabet et al., 2003).”

“Previous studies have demonstrated that TMS pulses delivered over Oz can elicit light sensations, called stationary phosphenes (Meyer et al. 1991; Marg and Rudiak 1994; Kammer 1999; Antal et al. 2003).”

“Modeling and experimental work suggest that the spatial resolution of direct TMS stimulation is 5–10 mm (11, 41).”

“Early studies (e.g. Kammer (1999)) have demonstrated a relatively good topographic correspondence between TMS-induced phosphenes and TMSinduced visual field deficits (scotomas) induced from several stimulation sites, suggesting that phosphenes could aid as a guide for visual stimulus alignment in…”

“1B), TMS can induce percepts such as of sparking lights, so-called phosphenes, in specific visual field locations depending upon retinotopic representation of stimulated occipital (Amassian et al., 1989; Elkin-Frankston et al., 2010; Fernandez et al., 2002; Kammer, 1999; Kammer et al., 2005a; Kammer et al., 2005b) or…”

“Unlike phosphenes induced by TMS over V1 [25], the phosphenes induced by occipital stimulation were not restricted to the lower visual field; they appeared in both the upper and lower visual fields.”

“…to the central sulcus most effectively evokes MEPs (Mills et al., 1992), whereas for the visual cortex on average an anterior-to-posterior direction (Kammer, 1999) or lateral-to-medial direction (Kammer et al., 2001a) most effectively evokes phosphenes (with optimal direction depending on…”

“Several laboratories use phosphenes as a routine procedure [6,7,13] and these report that the perceived form of the phosphene also tends to be stable over time.”

“There are few examples when NIBS alone is sufficient to produce motor behavior or a perceptual phenomenon, such as the well-established induction of muscle responses as quantified by themotor-evoked potentials (MEPs) or phosphenes (illusory perceptions of light) after TMS of the primary motor and visual cortex, respec…”

“In the case of the visual system, phosphenes can be elicited with stimulus intensities somewhat lower than those causing elevated perception thresholds (Kastner et al. 1998; Kammer, 1999).”

“These coordinates are most likely to correspond to visual cortical areas V1 ⁄ V2 in the case of foveal phosphenes and V2 ⁄ V3 for the unilateral phosphenes (Kastner et al., 1998; Kammer, 1999).”

“Previous studies have demonstrated that TMS pulses delivered to the occipital cortex can elicit light sensations called phosphenes (Meyer et al. 1991; Marg and Rudiak et al. 1994; Kammer 1999).”

“Sensations such as tingles evoked by direct activation of SI might be analogous to phosphenes, which can be induced by direct activation of visual cortex [72].”

“Also consistent with the feedback interpretation, the disk was perceived more frequently when the TMS elimidisk reports may have been due to the induction of phosphenes by TMS [9], which were misattributed to nated the annulus from visual awareness [12].”

“It has been established that TMS-induced phosphenes are due to focal stimulation of the visual cortex and exhibit topographic relationship with the retinotopic early visual areas (Kammer, 1999; Kammer et al., 2001).”

“The forms observed were similar to those described previously (Kammer, 1999).”

“found for visual suppression induced by occipital TMS (Amassian et al. 1994; Epstein and Zangaladze 1996; Kamitani and Shimojo 1999; Kammer 1999; Kastner et al. 1998; Potts et al. 1998).”

“First, reports of rTMS-induced visual masking are conWned to disruption of early visual areas (Kammer 1999).”

“In addition, the minimal distance does not violate the spatial specificity of TMS (occipital TMS has been shown to have a spatial resolution of ~10 mm; see Kammer, 1999).”

“We have shown previously that stimulation over this region principally excites V1 (Cowey and Walsh 2000; Pascual-Leone and Walsh 2001; see also Kammer 1999) and will use this shorthand throughout.”

“Previous studies demonstrated that TMS pulses delivered to the occipital cortex can elicit light sensations, called stationary phosphenes ( Kammer, 1999; Marg & Rudiak, 1994; Meyer, Diehl, Steinmetz, Britton, & Benecke, 1991).”

“With a fixed β of −0.3 (Kammer et al. 1999), SOA 0 is +72.06 ms and α 51.53 (χ 2 =44.36, R 2 =0.77) can be seen as an inversion of the previous method, in which the two criterion variables, contrast and proportion correct, are linked by the psychometric function.”

“TMS may also elicit unstructured white or coloured phosphenes in the visual ®eld (Barker et al., 1985; Meyer et al., 1991; Ray et al., 1998; Kammer, 1999; Cowey and Walsh, 2000; Stewart et al., 2001).”

“It has been shown that phosphenes overlap in space with scotomas (perceptual suppression) and can thus serve as a guide to maximize TMS effects on visual functions (Kammer, 1999).”

“This competency covers cortical mapping of non-motor areas, specifically phosphenes elicited from stimulation of visual areas (Marg and Rudiak 1994; Kammer 1999; Kammer et al. 2005) and the induction of speech arrest from online repetitive stimulation of Broca’s area (Pascual-Leone et al.”

“Although recent studies suggest a lateral preference for current orientation for phosphene induction [Kammer, 1999], we used the cranio-caudal direction used in most previous MT and PT studies [Antal et al.”

“By superimposing the visual field mappings of TMS interference with subjective drawings of phosphenes, Kammer (1999) suggested that TMS interference effects and phosphenes are generated by the same process.”

“For example, single pulse TMS applied to the primary motor cortex induces muscle twitches that can be recorded with an electromyogram (EMG) (Barker et al., 1985), while single pulse TMS to the occipital cortex can produce subjective light flashes ( Kammer, 1999 ).”

“In contrast to the disruptive effects on visual perception, singlepulse TMS over occipital cortex can also induce the percept of a light flash, i.e. phosphene (Cowey & Walsh, 2000; Kammer, 1999; Meyer et al., 1991).”

“The most detailed investigation of this phenomenon is provided by Kammer (1999) and Kammer et al. (2005a,b) and our prior knowledge of the representation of the retina in the striate cortex Phil.”

“When comparing our findings with those obtained in human visual cortex, we can assume that moderate effects elicited with 30% stimulus strength (relatively few neurons excited) may be comparable with the threshold for eliciting weak phosphene sensations, while stronger stimuli evoke increased population background act…”

“We have attempted to introduce such a evoke localized phosphenes [23,26,28,37], other studies systematic protocol.”

“Its spatial resolution, estimated to be approximately 1–2 cm in the visual cortex depending on stimulation parameters (Kammer, 1999), enables TMS to differentially stimulate nearby cortical regions, and it has been used to demonstrate functional dissociations between visual areas such as primary visual cortex and V5/M…”

“We determined the discrimination thresholds for vernier acuity with TMS masking (Kammer et al. 2003). At an SOA of 120 ms, TMS increased vernier discrimination threshold from about 25 to about 100 arc sec. These Wndings demonstrate that it is possible to measure TMS masking eVects with constant luminances of the visua…”

“To determine the phosphene threshold (PT), the coil was placed tangentially over the occipital pole (Kammer, 1999).”

“Phosphenes induced by occipital cortex stimulation likely include activity in early visual cortex [32,33].”

“Several types of visual recognition tasks have been disrupted by TMS applied over the occipital pole at various delays from the letter or the word presentation onset (e.g., Cowey & Walsh, 2000; Corthout, Uttl, Walsh, Hallett, & Cowey, 1999; Corthout, Uttl, Ziemann, Cowey, & Hallett, 1999; Kammer, 1999; Kastner, Demmer…”

“They are usually amorphous, but can develop into geometric patterns: their appearance depends on the stimulated location of the visual pathway (Marg and Rudiak 1994; Kammer 1999).”

“Changing the coil position also alters phosphene location, reflecting the point-to-point retinotopic organization of early visual areas [3,6,7].”

“…mechanisms are still unsettled but several studies suggest V1 possibly including V2/V3 as responsible sites (Amassian et al. 1994; Cowey and Walsh 2000; Kammer 1999, 2007; Kammer et al. 2001, 2005; Kastner et al. 1998; Meyer et al. 1991; Pascual-Leone and Walsh 2001; Sparing et al. 2002).”

“Previous work indicated that phosphenes can be induced in both hemispheres (Marg and Rudiak 1994; Kammer 1999; Kammer et al. 2005), and suggests that cortical excitability does not differ between hemispheres in occipital areas V2 and V3 (Kammer et al.”

“Phosphenes were considered to be elicited when the following criteria were met: Phosphenes could be localized in both left and right hemispheres, phosphenes were elicited with eyes shut, and phosphenes moved with fixation (Kammer, 1998).”

“The optimum site for phosphene generation is around the inion, targeting the area of striate cortex that receives projections from around the centre of the visual field, where the phosphene is typically reported as a point flash of light (Cowey & Walsh, 2000; Kammer, 1999).”

“A single pulse can stimulate neurons at rest, with observable behavioral (motor response; e.g., Barker et al., 1985) or perceptual (phosphenes; e.g., Marg and Rudiak, 1994; Kammer, 1999) consequences.”

“Kammer 1999; Sparing et al. 2005) as well as the analysis of single visual evoked potentials”

“In this work, we used functional magnetic resonance imaging (fMRI) to detect brain activation during local TMS of the occipital cortex in twelve healthy subjects.”

“Phosphenes can occur not only through external stimuli, but also through drugs [2,3], ionizing radiation [4–7], electrical [8–13], or magnetic stimulation [14–19] of the visual cortex, such as via Transcranial Magnetic Stimulation (TMS) [14–19].”

“(1991), only two studies had subjects observe phosphenes with opened eyes in order to immediately draw what they had seen (Kammer 1999; Cowey and Walsh 2000).”

“…of the occipital cortex (e.g., Cowey & Walsh, 2000; Corthout, Uttl, Walsh, Hallett, & Cowey, 1999; Corthout, Uttl, Ziemann, Cowey, & Hallett, 1999; Kammer, 1999; Kastner, Demmer, & Ziemann, 1998; Amassian, Cracco, et al., 1993; Amassian, Maccabee, et al., 1993; Amassian, et al., 1989, 1998).”

“apparently, phosphenes are generated in primary (V1) and extrastriate visual cortical areas (V2–V3) (Kammer 1999), with V1 being fundamental for phosphene awareness (cowey and Walsh 2000; Pascual-leone and Walsh 2001); nevertheless, other studies point to a subcortical origin (e.”

“Moreover, TMS studies of phosphenes and striate cortex topography (Kastner et al. 1998; Kammer 1999) and of visual hemifields (Amassian et al. 1993) suggest that striate cortex can be focally stimulated.”

“With most brain stimulation methods, we are only able to target shallow cortical regions (Kammer, 1998; Roth et al., 2007).”

“A comparable technique also exists for the visual cortex whereby single pulse TMS of the occipital pole can be used to evoke the percept of a phosphene [8].”

“The phosphenes are described as whitish flashes but sometimes they are colored (A ´ fra et al. 1998; Aurora et al. 1998; Gothe et al. 2002; Kammer 1999; Kammer et al. 2001; Kastner et al. 1998).”