Shih-Cheng Yen

Ultra-thin flexible polyimide neural probe embedded in a dissolvable maltose-coated microneedle

The ultra-thin flexible polyimide neural probe can reduce the glial sheath growth on the probe body while its flexibility can minimize the micromotion between the probe and brain tissue. To provide sufficient stiffness for penetration purposes, we developed a drawing lithography technology for uniform maltose coating to make the maltose-coated polyimide neural probe become a stiff microneedle. The coating thicknesses under different temperature and the corresponding stiffness are studied. It has been proven that the coated maltose is dissolved by body fluids after implantation for a few seconds. Moreover, carbon nanotubes are coated on the neural probe recording electrodes to improve the charge delivery ability and reduce the impedance. Last but not least, the feasibility and recording characteristic of this ultra-thin polyimide neural probe embedded in a maltose-coated microneedle are further demonstrated by in vivo tests.

Perceptual grouping in striate cortical networks mediated by synchronization and desynchronization

One advantage of cortical synchronization as a binding mechanism is its ability to account for phenomena such as perceptual grouping. Such a mechanism requires the ability to synchronize groups of cells and to desynchronize these groups from each other. We present a striate cortical model of perceptual grouping in which synchronization and desynchronization is carried out by a single, common mechanism. Cortical pyramidal cells and interneurons are simulated using multi-compartmental models. Cells in different orientation columns are inter-connected via two sets of long-distance connections that differ in axonal delays and spatial projections. The relative influence of these two connections determines whether synchronization or desynchronization occurs. Once one group of cells synchronizes, inputs from these cells facilitate synchronization in other orientation columns. We address the role of these synchronizing and desynchronizing connections in mediating perceptual grouping and metastable percepts.

Motion saliency outweighs other low-level features while watching videos

The importance of motion in attracting attention is well known. While watching videos, where motion is prevalent, how do we quantify the regions that are motion salient? In this paper, we investigate the role of motion in attention and compare it with the influence of other low-level features like image orientation and intensity. We propose a framework for motion saliency. In particular, we integrate motion vector information with spatial and temporal coherency to generate a motion attention map. The results show that our model achieves good performance in identifying regions that are moving and salient. We also find motion to have greater influence on saliency than other low-level features when watching videos.

Natural Movies Evoke Spike Trains with Low Spike Time Variability in Cat Primary Visual Cortex

Neuronal responses in primary visual cortex have been found to be highly variable. This has led to the widespread notion that neuronal responses have to be averaged over large numbers of neurons to obtain suitably invariant responses that can be used to reliably encode or represent external stimuli. However, it is possible that the high variability of neuronal responses may result from the use of simple, artificial stimuli and that the visual cortex may respond differently to dynamic, naturalistic images. To investigate this question, we recorded the responses of primary visual cortical neurons in the anesthetized cat under stimulation with time-varying natural movies. We found that cortical neurons on the whole exhibited a high degree of spike count variability, but a surprisingly low degree of spike time variability. The spike count variability was further reduced when all but the first spike in a burst were removed. We also found that responses exhibiting low spike time variability exhibited low spike count variability, suggesting that rate coding and temporal coding might be more compatible than previously thought. In addition, we found the spike time variability to be significantly lower when stimulated by natural movies as compared with stimulation using drifting gratings. Our results indicate that response variability in primary visual cortex is stimulus dependent and significantly lower than previous measurements have indicated.

Progress of Flexible Electronics in Neural Interfacing - A Self-Adaptive Non-Invasive Neural Ribbon Electrode for Small Nerves Recording.

A novel flexible neural ribbon electrode with a self-adaptive feature is successfully implemented for various small nerves recording. As a neural interface, the selective recording capability is characterized by having reliable signal acquisitions from the sciatic nerve and its branches such as the peroneal nerve, the tibial nerve, and the sural nerve.

Modelling and design of a synergy-based actuator for a tendon-driven soft robotic glove

The need for a means of assistance in human grasping, to compensate for weakness or to augment performance, is well documented. An appealing new way of doing so is through soft, wearable robots that work in parallel with the human muscles. In this paper we present the design and modelling of a tendon-driving unit that empowers a wearable, soft glove. Being portability one of our main objectives, we use only 1 motor to move 8 degrees of freedom of the hand. To achieve this we use an underactuation strategy based on the human hands first postural synergy, which explains alone ≈60% of activities of daily living. The constrains imposed by the underactuation strategy are softened, to allow adaptability during grasping, by placing elastic elements in series with the tendons. A simulation of the dynamic behaviour of the glove on a human hand allows us to quantify the magnitude and distribution of the forces involved during usage. These results are used to guide design choices such as the power of the motor and the stiffness of the springs. The designed tendon-driving unit comprises a DC motor which drives an array of spools dimensioned according to the first postural synergy, an electromechanical clutch to hold the hand in position during static posture and a feeder mechanism to avoid slacking of the tendons around the spool. Finally, the tendon-driving unit is tested to verify that it satisfies motion and force characteristics required to assist its wearer in activities of daily living.

Flexible Epineural Strip Electrode for Recording in Fine Nerves

This paper demonstrates flexible epineural strip electrodes (FLESE) for recording from small nerves. Small strip-shaped FLESE enables us to easily and closely stick on various sized nerves for less damage in a nerve and optimal recording quality. In addition, in order to enhance the neural interface, the gold electrode contacts were coated with carbon nanotubes, which reduced the impedance of the electrodes. We used the FLESEs to record electrically elicited nerve signals (compound neural action potentials) from the sciatic nerve in rats. Bipolar and differential bipolar configurations for the recording were investigated to optimize the recording configuration of the FLESEs. The successful results from differential bipolar recordings showed that the total length of FLESEs could be further reduced, maintaining the maximum recording ability, which would be beneficial for recording in very fine nerves. Our results demonstrate that new concept of FLESEs could play an important role in electroceuticals in near future.

A Smartphone-Centric System for the Range of Motion Assessment in Stroke Patients

The range of motion (ROM) in stroke patients is often severely affected. Poststroke rehabilitation is guided through the use of clinical assessment scales for the rROM. Unfortunately, these scales are not widely utilized in clinical practice as they are excessively time-consuming. Although commercial motion-capture systems are capable of providing the information required for the assessments, most systems are either too costly or lack the convenience required for assessments to be conducted on a daily basis. This paper presents the design and implementation of a smartphone-based system for automated motor assessment using low-cost off-the-shelf inertial sensors. The system was used to automate a portion of the upper-extremity Fugl-Meyer assessment (FMA), which is widely used to quantify motor deficits in stroke survivors. Twelve out of 33 items were selected, focusing mainly on joint angle measurements of the upper body. The system has the ability to automatically identify the assessment item being conducted, and calculate the maximum respective joint angle achieved. Preliminary results show the ability of this system to achieve comparable results to goniometer measurements, while significantly reducing the time required to conduct the assessments. The portability and ease-of-use of the system would simplify the task of conducting range-of-motion assessments.

Mixed selectivity morphs population codes in prefrontal cortex

The prefrontal cortex maintains working memory information in the presence of distracting stimuli. It has long been thought that sustained activity in individual neurons or groups of neurons was responsible for maintaining information in the form of a persistent, stable code. Here we show that, upon the presentation of a distractor, information in the lateral prefrontal cortex was reorganized into a different pattern of activity to create a morphed stable code without losing information. In contrast, the code in the frontal eye fields persisted across different delay periods but exhibited substantial instability and information loss after the presentation of a distractor. We found that neurons with mixed-selective responses were necessary and sufficient for the morphing of code and that these neurons were more abundant in the lateral prefrontal cortex than the frontal eye fields. This suggests that mixed selectivity provides populations with code-morphing capability, a property that may underlie cognitive flexibility.Neurons in the lateral prefrontal cortex (but not the frontal eye fields) appear to maintain working memory information when disrupted by a transient distractor, not by using an immutable persistent code but by morphing from one persistent code to another. This code-morphing may provide the lateral prefrontal cortex with cognitive flexibility.

Wireless Power Delivery to Flexible Subcutaneous Implants Using Capacitive Coupling

Implantable devices need sustainable wireless powering for safe long-term operations. In this paper, we present a near-field capacitive coupling (NCC)-based wireless powering scheme to transfer power to implants efficiently. By modeling the power link, we identify that the optimal operating frequency of the NCC scheme for subcutaneous power delivery is in the sub-GHz frequency range. The proposed scheme has desirable features, such as flexible and conformal power receiver realizations, and complies well with IEEE C95.1 specific absorption rate safety standards. The NCC link was designed and tested in a nonhuman primate cadaver, and the experimental results showed that it could safely deliver up to 100 mW of power to an implant with a peak operating efficiency of over 50%. A bending deformation study of the transmitter–receiver patches was also performed to demonstrate the reliability of the NCC powering scheme, in realistic postimplantation scenarios. Our studies validate the NCC method as a safe wireless powering scheme, which can be used as an alternative to the near-field resonant inductive coupling method, for chronic use in subcutaneous implants.