ABSTRACT
We describe the development and evaluation of a computer-controlled system for delivering odors in a magnetic resonance imaging (MRI) environment. The system allows a timely presentation of different odors in synchrony with MRI sequences and participant's inspiration phase. The rise/fall time of odor deliverance has been optimized to generate prompt and strong stimulations. Equipped with a user-friendly programming interface, the system can be used reliably in a wide range of experimental paradigms. We have paid particular attention to developing a portable system that is relatively easy, rapid, and inexpensive to replicate. The equipment has been tested in a 3-Tesla MRI in a boxcar paradigm, in which stimulation conditions alternated with rest periods (no stimulation). The experiment demonstrated the good functioning of the device and its efficiency in producing the expected activation in the olfactory cortex; it also revealed some methodological and technical aspects to be improved.
Subject(s)
Automation, Laboratory/instrumentation , Brain/physiology , Magnetic Resonance Imaging , Odorants , Olfactory Perception/physiology , Brain Mapping , Humans , Image Processing, Computer-AssistedABSTRACT
PURPOSE: To examine the visual evoked potentials (VEP) and electroretinograms (ERG) generated during electrical stimulation of the human optic nerve using the optic nerve visual prosthesis. METHODS: Two volunteers blind from retinitis pigmentosa (RP) and with no light perception each received a chronically implanted optic nerve visual prosthesis. Cortical evoked potentials were recorded using 16 scalp electrodes, and antidromic ERGs were obtained using DTL electrodes while the optic nerve was electrically stimulated. The results were compared with flash and eye surface electrical stimulation results in normal-sighted control subjects. RESULTS: The VEPs obtained in our two volunteers with implants had a waveshape similar to that obtained in normal-sighted volunteers during flash stimulation, but latency was reduced by approximately 25 ms. The VEPs recorded during surface eye stimulation are similar in both normal-sighted and RP volunteers. The VEPs were compared at sub- and supra-threshold stimulation strength and with different electrode configurations. Finally, the antidromic ERG recordings obtained in our implanted volunteers show a unique inner retinal potential generated by retrograde stimulation of the eye from the optic nerve. CONCLUSIONS: Evoked potentials can be used to examine how a visual prosthesis generates visual sensations. This provides an objective means to investigate various aspects of the visual prostheses.
Subject(s)
Electric Stimulation/instrumentation , Electrodes, Implanted , Evoked Potentials, Visual/physiology , Optic Nerve/physiology , Aged , Blindness/etiology , Blindness/rehabilitation , Electroretinography , Female , Humans , Male , Photic Stimulation , Prostheses and Implants , Retina/physiology , Retinitis Pigmentosa/complications , Visual Cortex/physiologyABSTRACT
PURPOSE: This study involved a volunteer completely blind from retinis pigmentosa who had previously been implanted with an optic nerve visual prosthesis. The aim of this two-year study was to train the volunteer to localize a given object in nine different positions, to discriminate the object within a choice of six, and then to grasp it. METHODS: In a closed-loop protocol including a head worn video camera, the nerve was stimulated whenever a part of the processed image of the object being scrutinized matched the center of an elicitable phosphene. The accessible visual field included 109 phosphenes in a 14 degrees x 41 degrees area. RESULTS: Results showed that training was required to succeed in the localization and discrimination tasks, but practically no training was required for grasping the object. The volunteer was able to successfully complete all tasks after training. The volunteer systematically performed several left-right and bottom-up scanning movements during the discrimination task. Discrimination strategies included stimulation phases and no-stimulation phases of roughly similar duration. CONCLUSION: This study provides a step towards the practical use of the optic nerve visual prosthesis in current daily life.
Subject(s)
Blindness/surgery , Discrimination, Psychological/physiology , Hand Strength/physiology , Optic Nerve/physiopathology , Prostheses and Implants , Vision, Ocular/physiology , Blindness/rehabilitation , Discrimination, Psychological/radiation effects , Electric Stimulation/methods , Female , Humans , Longitudinal Studies , Middle Aged , Optic Nerve/radiation effects , Retrospective Studies , Time Factors , Vision, Ocular/radiation effects , Visual Perception/physiology , Visual Perception/radiation effectsABSTRACT
A volunteer with retinitis pigmentosa and no residual vision was chronically implanted with an optic nerve electrode connected to an implanted neurostimulator and antenna. An external controller with telemetry was used for electrical activation of the nerve which resulted in phosphene perception. Open-loop stimulation allowed the collection of phosphene attributes and the ability to elicit perception of simple geometrical patterns. Low perception thresholds allowed for large current intensity range within safety limits. In a closed-loop paradigm, the volunteer was using a head-worn video camera to explore a projection screen. The volunteer underwent performance evaluation during the course of a training program with 45 simple patterns. After learning, the volunteer reached a recognition score of 63% with a processing time of 60 s. Mean performance in orientation discrimination reached 100% with a processing time of 8 s.
