Tohru Yagi

Transretinal Electrical Stimulation with a Suprachoroidal Multichannel Electrode in Rabbit Eyes

PurposeSeveral approaches for placing an electrode device for visual prosthesis have been previously proposed. In this study, we investigated if transretinal stimulation from the suprachoroidal space can elicit an electrical evoked potential (EEP) in albino rabbits.MethodsA flat electrode array (polyimide plate, platinum electrode) was developed and used for this study. After performing a scleral incision at 2–2.5 mm from the limbus and placing an anchoring suture, the array was inserted into the suprachoroidal space in the posterior portion of the eye by direct observation under a microscope. A platinum wire was implanted into the vitreous space as a reference electrode. For electrical stimulation, a biphasic pulse was used. When the electrode was stimulated, the EEP was recorded.ResultsWhen the electrical stimulation from the suprachoroidal space was applied, the EEP could be recorded with an epidural electrode, and the threshold was 66.0 ± 32.1μA (42.0μC/cm2). Histological examination indicated the absence of major damage to the retina and choroid from the insertion and placement of the array and the electrical stimulation.ConclusionsTransretinal electrical stimulation from the suprachoroidal space could elicit EEP, suggesting that this approach may be useful for a retinal prosthesis system.

A Study on the Frontal Cortex in Cognitive Tasks using Near-Infrared Spectroscopy

The frontal cortex is the part of the brain that relates to higher brain functions, such as logical thinking and emotion. As part of the development of a brain-computer interface, we tested whether the frontal cortex reacts differently in people as they performed three different cognitive tasks. The reaction of the cortex was tested using near-infrared spectroscopy. Our preliminary research results showed a difference in blood flow volume occurred before and after two assigned tasks: a math task and a word task. However, after a naming task there was no particular reaction. We believe that mental stress might be the cause of the difference in frontal cortex activity.

Drifting and Blinking Compensation in Electro-oculography (EOG) Eye-gaze Interface

This paper describes an eye-gaze interface using a biological signal, electro-oculorgram (EOG). This interface enables a user to move a computer cursor on a graphical user interface using eye gaze movement alone. It will be useful as a communication aid for individuals with mobility handicaps. Although EOG is easily recordable, drifting and blinking problems must be solved to produce a reliable eye-gaze interface. Here we introduced a calibration method and a feedback control to overcome these problems.

Hybrid retinal implant: fusion of engineering and neuroscience

A hybrid retinal implant is a visual prosthesis to reconstruct visual sensation in the blind. It consists of an external devise and an internal micro-electro mechanical system (MEMS). In order to connect the MEMS with the central nervous systems (CNS), several neurons are attached on the top of the MEMS, and their axons are guided with the peripheral nerve graft or the fiber filled with Schwann cells. After the axons reach the CNS to make functional connection with the CNS neurons, the adequate electrical stimulation will make the attached neurons produce the action potential so that it will be possible to send image signal to the CNS through the neurons. Namely, the attached neurons can be used as living electric wires in the hybrid retinal implant.

Direct Gaze Estimation Based on Nonlinearity of EOG

Electrooculography (EOG) is one of the measures used to estimate the direction of a persons gaze; however, conventional EOG techniques suffer from a drift issue which makes it difficult to extract an accurate absolute eye angle. The technique proposed here is based on the nonlinearity of the EOG and offers a practical solution to this problem. It estimates the absolute eye angles before and after a saccade, which cancels the offset due to the drift. Additionally, it does not require any effort from the user or any target, but instead uses only the difference of the EOGs. Experiments with five subjects confirm that the proposed technique can estimate the absolute eye angle with an error of less than

A computational study on an electrode array in a hybrid retinal implant

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Research of the characteristics of Alzheimer’s disease using EEG

. They also show improvements are achieved with several options such as weighting and multiple saccades. The technique will contribute to practical EOG-based interaction systems.

Conductive rubber electrodes for earphone-based eye gesture input interface

The authors propose a neural interface for a retinal implant. This interface consists of neural cells and a electrode array. After implantation, the cells are expected to receive nutrients from surrounded tissues, then develop their axon. If the axons reach towards the central nervous system to make the proper synaptic connection, then adequate electrical stimulation will lead the neural cells to produce the action potential so that functional connection will be realized. The authors introduce their current achievement and future work.

Study on mental stress using near-infrared spectroscopy, electroencephalography, and peripheral arterial tonometry

In this paper, we propose a new method for diagnosing Alzheimer’s disease (AD) on the basis of electroencephalograms (EEG). The method, which is termed “Power Variance Function (PVF) method”, indicates the variance of the power at each frequency. By using the proposed method, the power of EEG at each frequency was calculated using Wavelet transform, and the corresponding variances were defined as PVF. After the PVF histogram of 42 healthy people was approximated as a Generalized Extreme Value (GEV) distribution, we evaluated the PVF of 10 patients with AD and 10 patients with mild cognitive impairment (MCI). As a result, the values for all AD and MCI subjects were abnormal. In particular, the PVF in the θ band for MCI patients was abnormally high, and the PVF in the α band for AD patients was low.

Active vision inspired by mammalian fixation mechanism

An eartip made of conductive rubber that also realizes biopotential electrodes is proposed for a daily-use earphone-based eye gesture input interface. Several prototypes, each with three electrodes to capture electrooculogram (EOG), are implemented on earphones and examined. Experiments with one subject over a 10-day period reveal that all prototypes capture EOG similarly but they differ as regards stability of the baseline and the presence of motion artifacts. Another experiment conducted on a simple eye-controlled application with six subjects shows that the proposed prototype minimizes motion artifacts and offers good performance. Artifacts induced by daily motion while wearing the proposed electrode and eye gesture performance are also measured, and we discuss how to deal with them. We conclude that conductive rubber with mixed Ag filler is the most suitable setup in our experiment.