Phosphene-guided transcranial magnetic stimulation of occipital but not parietal cortex suppresses stimulus visibility

Abstract

Transcranial magnetic stimulation (TMS) applied over the occipital lobe approximately 100 ms after the onset of a stimulus decreases its visibility if it appears in the location of the phosphene. Because phosphenes can also be elicited by stimulation of the parietal regions, we asked if the same procedure that is used to reduce visibility of stimuli with occipital TMS will lead to decreased stimulus visibility when TMS is applied to parietal regions. TMS was randomly applied at 0 to 130 ms after the onset of the stimulus (SOA) in steps of 10 ms in occipital and parietal regions. Participants responded to the orientation of the line stimulus and rated its visibility. We replicate previous reports of phosphenes from both occipital and parietal TMS. As previously reported, we also observed visual suppression around the classical 100 ms window both in the objective line orientation and subjective visibility responses with occipital TMS. Parietal stimulation, on the other hand, did not consistently reduce stimulus visibility in any time window.

Prophylactic treatment in menstrual migraine: A proof-of-concept study

“…Although the perception of phosphenes is somewhat subjective, in recent years several studies on the visual cortex in healthy subjects and in patients, have used the intensity threshold at which phosphenes are elicited as a specific index of visual cortex excitability (e.g. [3,13,22,27,31,51,52,56]). The exact generation of phosphene perception is still under discussion, results suggest that PTs are not functionally analogous to motor-evoked potentials following TMS over M1 but more to conscious perception of visual stimuli, nevertheless occurring within an earlier time window [52].…”

The influence of posterior parietal cortex on extrastriate visual activity: A concurrent TMS and fast optical imaging study

“…Analysis of phosphene reports revealed that subjects perceived a greater proportion of phosphenes with P3 stimulation than control site stimulation (P3 TMS: M= 55.7%, SD=19.1%; control site TMS: M=33.5%, SD=34.94%; t(9)=2.61, p=.028), consistent with greater activation of PPC with P3 stimulation than control site stimulation (Bagattini et al, 2015; Fried et al, 2011; Marzi et al, 2009; Mazzi et al, 2014; Tapia et al, 2014). However, it should be noted that the relatively high rate of phosphene reports associated with control site stimulation may indicate some spread of activation to left PPC during control site TMS.…”

“…Stimulation over this scalp location corresponds to BA 7/39/40 (Herwig et al 2003; Okamoto et al, 2004). We verified that coil position induced suprathreshold stimulation of PPC by ensuring that TMS to this location elicited a phosphene percept (Bagattini et al, 2015; Fried et al, 2011; Marzi et al, 2009; Mazzi et al, 2014; Tapia et al, 2014). We selected a stimulation site that elicited parietal phosphenes so that stimulation intensity could be set according to this phosphene threshold to ensure suprathreshold stimulation of PPC.…”

“…In order to ensure that parietal stimulation was sufficient to influence the brain we used the presence of TMS-induced phosphenes; if TMS resulted in a visual percept we could be sure that it was impacting cortical activity. Previous work has established that, like occipital TMS, a phosphene percept can be also induced with TMS to parietal cortex (Bagattini, Mazzi, & Savazzi, 2015; Fried, ElkinFrankston, Rushmore, Hilgetag, & Valero-Cabre, 2011; Marzi, Mancini, & Savazzi, 2009; Mazzi, Mancini, & Savazzi, 2014; Tapia, Mazzi, Savazzi, & Beck, 2014). Thus, subjects were pre-screened for reliability of parietal phosphene percept.…”

Using brain stimulation to disentangle neural correlates of conscious vision

“…And while one recent study did not obtain consistent visual suppression by TMS pulses over these parietal regions (Tapia et al, 2014), Koivisto et al (2014) did report evidence for parietal (inferior parietal sulcus) TMS masking of specifically subjective conscious vision.…”