Mapping of the human visual cortex using image-guided transcranial magnetic stimulation.
ABSTRACT We describe a protocol using transcranial magnetic stimulation (TMS) to systematically map the visual sensations induced by focal and non-invasive stimulation of the human occipital cortex. TMS is applied with a figure of eight coil to 28 positions arranged in a 2x2-cm grid over the occipital area. A digitizing tablet connected to a PC computer running customized software, and audio and video recording are used for detailed and accurate data collection and analysis of evoked phosphenes. A frameless image-guided neuronavigational device is used to describe the position of the actual sites of the stimulation coils relative to the cortical surface. Our results show that TMS is able to elicit phosphenes in almost all sighted subjects and in a proportion of blind subjects. Evoked phosphenes are topographically organized. Despite minor inter-individual variations, the mapping results are reproducible and show good congruence among different subjects. This procedure has potential to improve our understanding of physiologic organization and plastic changes in the human visual system and to establish the degree of remaining functional visual cortex in blind subjects. Such a non-invasive method is critical for selection of suitable subjects for a cortical visual prosthesis.
Full-textDOI: · Available from: Alvaro Pascual-Leone, May 18, 2015
SourceAvailable from: Cristina Soto[Show abstract] [Hide abstract]
ABSTRACT: Visual prosthesis development relays in the ability of the vi-sual system to evoke visual topographically organized perceptions called phosphenes when it is electrically stimulated. There have been many approaches to quantify phosphenes and describe their position in the vi-sual field but no one managed to be accurate and easy to be handled by visually impairment individuals. Here, we present a highly accurate, intuitive and freely movement method to draw phosphenes in the 3D visual space. We use an infrared sensor from the commercial Kinect hardware through a customized software to detect the movements of the subjects drawing on the air in the same 3D coordinate were they perceive the phosphenes.With this new technique we introduce the com-ponent of depth of the visual space in the phosphenes mapping, a disre-garded component in the old 2D techniques. No techniques in the past had this measurement in account but our results show that transcraneal magnetic stimulated subjects clearly perceived phosphenes at different depth locations (data not shown at this paper). Furthermore this new mapping technique has three main advantages: (i) it allows patients to locate phosphenes in the real 3D visual space were they perceive the phosphenes, (ii) allows a quantitative measurement of the area and shape of the phosphenes (iii) and avoid the interactions between external de-vices and patients in order to facilitate the performance to the low vision or blind individuals.Lecture Notes in Computer Science 06/2013; 7930:342-349. · 0.51 Impact Factor
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ABSTRACT: A MRI-guided navigation solution for repetitive transcranial magnetic stimulation (rTMS)was designed in this study which integrates optical positioning system to perform positioning and tracking of the magnetic stimulation coil in real-time. The system includes the following procedures: segmentation and 3D reconstruction of brain anatomy from T1-weighted (T1W) MRI, coil calibration and localization, spatial registration between the subject's head and the MRI data and 2D/3D navigation. The 2D/3D navigation provides the spatial relationship between actual sites of the coils and the cortical surface quantitively and allows visualization of the location and orientation of the coil over the brain/head. Verified through the experiments using a phantom human skull model and the head MRI data from a healthy human subject, the proposed navigation system was demonstrated to be flexible, safe, accurate and time efficient.Biomedical Engineering Applications Basis and Communications 03/2013; 25(01). DOI:10.4015/S1016237213500129 · 0.23 Impact Factor