Inducing lateralized phosphenes over the occipital lobe using transcranial magnetic stimulation to navigate a virtual environment

Abstract

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.

Guiding Human Navigation with Non-Invasive Vestibular Stimulation and Evoked Mediolateral Sway

“…In fact, only one participant answered incorrectly on a single trial, resulting in an overall accuracy level exceeding 99%. This result complements recent work guiding navigation with TMS 15 , extending the result to a new domain of NIBS and sensory augmentation, and extending beyond only left and right turn instructions to include the straight instruction. Interestingly, the vestibular cue induced by GVS was reliable enough to overcome the potential vestibular interference introduced by the optic ow of the VR system, and the mental demands of navigating under threat of electric shock.…”

“…Furthermore, we expect the extent of the sway (i.e., COP magnitude) to be positively related to the intensity of GVS, and that a control bipolar alternating current GVS condition would not reliably elicit COP deviations. Given research demonstrating that TMS can be used to effectively guide virtual environment navigation through phosphene elicitation 14,15 , we also hypothesized that individually calibrated GVS would be highly effective (i.e., accuracy levels exceeding 90%) at guiding virtual navigation by eliciting mediolateral sway in the direction of instructed movement.…”

“…Similarly, information can be communicated between humans and computers in sensory augmentation or substitution paradigms that extend, supplement, or transform a sensory modality typically relied upon to perform a task 13,14 . For example, TMS targeting the occipital cortex has been used to elicit lateralized phosphenes (arti cial percepts of light) to guide navigation through virtual environments 15 . In that study, participants received lateralized TMS to elicit contralateral visual phosphenes that cued participants to turn right or left in the absence of any natural navigation cues.…”