High-density Recording System Research Articles

High-density neural recording system design.

Implantable medical devices capable of monitoring hundreds to thousands of electrodes have received great attention in biomedical applications for understanding of the brain function and to treat brain diseases such as epilepsy, dystonia, and Parkinson's disease. Non-invasive neural recording modalities such as fMRI and EEGs were widely used since the 1960s, but to acquire better information, invasive modalities gained popularity. Since such invasive neural recording system requires high efficiency and low power operation, they have been implemented as integrated circuits. Many techniques have been developed and applied when designing integrated high-density neural recording architecture for better performance, higher efficiency, and lower power consumption. This paper covers general knowledge of neural signals and frequently used neural recording architectures for monitoring neural activity. For neural recording architecture, various neural recording amplifier structures are covered. In addition, several neural processing techniques, which can optimize the neural recording system, are also discussed.

High-density mapping of primate digit representations with a 1152-channel µECoG array

Objective. Advances in brain–machine interfaces (BMIs) are expected to support patients with movement disorders. Electrocorticogram (ECoG) measures electrophysiological activities over a large area using a low-invasive flexible sheet placed on the cortex. ECoG has been considered as a feasible signal source of the clinical BMI device. To capture neural activities more precisely, the feasibility of higher-density arrays has been investigated. However, currently, the number of electrodes is limited to approximately 300 due to wiring difficulties, device size, and system costs. Approach. We developed a high-density recording system with a large coverage (14 × 7 mm2) and using 1152 electrodes by directly integrating dedicated flexible arrays with the neural-recording application-specific integrated circuits and their interposers. Main results. Comparative experiments with a 128-channel array demonstrated that the proposed device could delineate the entire digit representation of a nonhuman primate. Subsampling analysis revealed that higher-amplitude signals can be measured using higher-density arrays. Significance. We expect that the proposed system that simultaneously establishes large-scale sampling, high temporal-precision of electrophysiology, and high spatial resolution comparable to optical imaging will be suitable for next-generation brain-sensing technology.

Interpixel crosstalk cancellation on holographic memory

In holographic memory systems, there have been no practical techniques to minimize interpixel crosstalk thus far. We developed an interpixel crosstalk cancellation technique using a checkerboard phase pattern with a phase difference of π/2, which can decrease the size of the spatial filter along the Fourier plane with the signal-to-noise ratio (SNR) kept high. This interpixel crosstalk cancellation technique is simple because it requires only one phase plate in the signal beam path. We verified the effect of such a cancellation technique by simulation. The improvement of SNR is maximized to 6.5 dB when the filter size specified in the Nyquist areal ratio is approximately 1.05 in ideal optical systems with no other fixed noise. The proposed technique can improve SNR by 0.85 in an assumed monocular architecture at an actual noise intensity. This improvement of SNR is very useful for realizing high-density recording or enhancing system robustness.

Studying the Retinal Source of Photophobia by Facial Electroretinography.

Photophobia is a debilitating clinical condition that disrupts the ability to use vision for everyday tasks in bright lighting conditions. The goal of the study is to develop a methodology to study the neural basis of photophobia and the contribution of the melanopic pathway to its etiology with differential chromatic responses by means of standard electroencephalographic recording equipment. We introduce and validate the approach of recording wavelength-specific electroretinographic (ERG) responses from the face electrodes of the high-density whole-head electroencephalography recording system under light-adapted conditions. ERGs recorded in this way to whole-field chromatic stimuli exhibit striking differences between the photophobic and non-photophobic groups. The control responses were consistent with photopic intensity in peak time, and in the ordering of peak times as a function of wavelength condition, indicating a predominantly cone source of the signals. The photophobic responses, on the other hand, were substantially slowed relative to controls, with the peak times conforming to a different order as a function of wavelength condition than controls, implying that the cone response has been suppressed and that the responses derived from a different photoreceptor system consistent with mediation by melanopic retinal ganglion cells. The results will be important for determining the neural pathways involved in photophobia and potential approaches to its treatment on the basis of this etiology.

P124 Real-time source-level EEG network activity state triggered TMS with millisecond resolution

Question Closed-loop methods that trigger the TMS pulse based on the EEG signal are increasingly available, however, current systems rely on the data of a small number of channels and the signal at sensor level cannot be localized to a specific brain area. The challenge is to analyze a sufficient number of EEG channels in real-time to enable spatially localized estimation of individual brain network activity. Methods EEG data is acquired using a high-density TMS compatible recording system and streamed online to a real-time digital processing system based on Simulink. A sliding window of data is used to estimate the sources that give rise to the EEG signal using a spatial filter computation executed on the processor as the signal is acquired. The forward model is computed based on the MRI data using a FEM model to solve the forward problem. The leadfields are calculated employing the neuronavigated electrode positions and then employed to compute the real-time LCMV beamforming. Instantaneous phase is estimated at multiple source-level location simultaneously using parallel sliding windows of band-pass filtered data preceding the current time, each extended into the future in real-time using autoregressive model, with instantaneous phase estimated using a Hilbert transform. Results A latency of Conclusions A novel technique enabling TMS triggered by the instantaneous phase-state of the individual network is presented. This is a significant extension of the current state-of-the-art and could enable the development of more effective personalized closed-loop neuromodulatory stimulation protocols.

High-Density Holographic Data Storage Using Three-Dimensional Shift Multiplexing with Spherical Reference Wave

In this study, we propose a three-dimensional shift multiplexing technique using a spherical reference wave. By utilizing a spherical reference wave, multiplex recording is enabled in this system by simply displacing the recording medium. The utilization of a spherical reference wave makes it possible to realize three-dimensional multiplexing, which uses parallel directions of the medium surface and thickness direction. It is also expected that this approach will improve the recording density as compared with the conventional multiplex technique. We report the numerical and experimental evaluation results of our high-density recording and reproduction system based on this principle.

Time Domain Analysis Of Nanoscale Electromagnetic Problems By A Boundary Integral Equation Method With Fast Inverse Laplace Transform

A novel computational technique is proposed for analysis of transient electromagnetic problems in nanoscale. Our proposed method can perform reliable and efficient simulation. We discuss time domain analysis of a nanoscale antenna to establish an ultra-fast and high-density magnetic recording system.

Electrophysiological correlates of fearful and sad distraction on target processing in adolescents with attention deficit-hyperactivity symptoms and affective disorders

In this study we used event-related brain potentials (ERP) as neural markers of cognitive operations to examine emotion and attentional processing in a population of high-risk adolescents with mental health problems that included attention deficit and hyperactivity disorder (ADHD), anxiety, and depression. We included a healthy control group for comparison purposes, and employed a modified version of the emotional oddball paradigm, consisting of frequent distracters (scrambled pictures), infrequent distracters (sad, fearful, and neutral pictures), and infrequent targets (circles). Participants were instructed to make a right hand button press to targets and a left hand button press to all other stimuli. EEG/ERP recordings were taken using a high-density 256-channel recording system. Behavioral data showed that for both clinical and non-clinical adolescents, reaction time (RT) was slowest in response to the fearful images. Electrophysiological data differentiated emotion and target processing between clinical and non-clinical adolescents. In the clinical group we observed a larger P100 and late positive potential (LPP) in response to fearful compared to sad or neutral pictures. There were no differences in these ERPs in the healthy sample. Emotional modulation of target processing was also identified in the clinical sample, where we observed an increase in P300 amplitude, and a larger sustained LPP in response to targets that followed emotional pictures (fear and sad) compared to targets that followed neutral pictures or other targets. There were no differences in these target ERPs for the healthy participants. Taken together, we suggest that these data provide important and novel evidence of affective and attention dysfunction in this clinical population of adolescents, and offer an example of the disruptive effects of emotional reactivity on basic cognition.

Seizure source imaging by means of FINE spatio-temporal dipole localization and directed transfer function in partial epilepsy patients

ObjectiveTo investigate the usage of a high-density EEG recording system and source imaging technique for localizing seizure activity in patients with medically intractable partial epilepsy. MethodsHigh-density, 76-channel scalp EEG signals were recorded in 10 patients with partial epilepsy. The patients underwent routine clinical pre-surgical evaluation and all had resective surgery with seizure free outcome. After applying a FINE (first principle vectors) spatio–temporal source localization and DTF (directed transfer function) connectivity analysis approach, ictal sources were imaged. Effects of number of scalp EEG electrodes on the seizure localization were also assessed using 76, 64, 48, 32, and 21 electrodes, respectively. ResultsSurgical resections were used to assess the source imaging results. Results from the 76-channel EEG in the 10 patients showed high correlation with the surgically resected brain regions. The localization of seizure onset zone from 76-channel EEG showed improved source detection accuracy compared to other EEG configurations with fewer electrodes. ConclusionsFINE together with DTF was able to localize seizure onset zones of partial epilepsy patients. High-density EEG recording can help achieve improved seizure source imaging. SignificanceThe present results suggest the promise of high-density EEG and electrical source imaging for noninvasively localizing seizure onset zones.

Category expectations: A differential modulation of the N170 potential for faces and words

The goal of the present study was to explore whether endogenous attention can be oriented to different perceptual categories and to examine how these expectations modulate visual stimulus processing. We designed a cueing paradigm that prepared participants, on a trial-by-trial basis, for the most likely stimulus category of the target, which could be either a face or a word. Participants were asked to discriminate the gender of the stimuli, regardless of their category. We measured participants’ brain activity by means of a high-density electroencephalographic recording system to investigate the neural correlates of orienting attention to faces and words. As expected, we observed a behavioural facilitation for valid compared to invalid trials. In addition, target expectations influenced stimulus processing at several points in time. Most importantly, attention modulated the lateralized N170 component in a category-specific fashion. These results show that, at least under certain circumstances, orienting endogenous attention to different categories can influence the perceptual stages of face and word visual processing.

Attention Modulates Initial Stages of Visual Word Processing

Selective attention has the potential to enhance the initial processing of objects, their spatial locations, or their constituent features. The present study shows that this capacity to modulate initial stages of processing also applies to linguistic attributes. A cueing paradigm focused attention at different levels of word representations on a trial-by-trial basis to study the time course of attentional modulation on visual word processing by means of a high-density electrophysiology recording system. Attention to different linguistic attributes modulated components related to semantic, phonological, and orthographic stages of word processing. Crucially, the N200, associated with initial stages of orthographic decoding, was enhanced by attention to the letter pattern of words. These results suggest that top-down attention has the capacity to enhance initial perceptual stages of visual word processing and support the flexibility of attention in modulating different levels of information processing depending on task goals.

Design Curves and Information-Theoretic Limits for Perpendicular Recording Systems

To optimize a high-density magnetic recording system, one needs to know the tradeoffs between various components of the system including the read/write transducers, the magnetic medium, and the read channel. In this paper, we consider a channel model characterized by three parameters: the replay pulse width T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> , the transition jitter noise standard deviation sigma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</sub> , and the signal-to-electronic-noise ratio SNR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WG</sub> . We utilize information-theoretic tools to determine the acceptable region for the channel parameters T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> and sigma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</sub> when optimal detection and linear coding techniques are used. This paper is an extension of a similar analysis for a system that utilized a minimum mean-squared error (MMSE) equalizer, a Viterbi detector, and a Reed-Solomon (RS) code. Our main conclusion is that there is a considerable potential gain to be achieved by using improved detection and coding schemes as compared with the present system

Radial motion measurement of a high-revolution spindle motor

In industrial fields, the non-repeatable run out (NRRO) of the high-revolution spindle of a high-density recording system is often estimated. In contrast, repeatable run out (RRO) is usually not estimated. A three-point method based on correction is useful when radial motion includes RRO. However, experiments conducted at high revolution (over 2000 rpm) have not yet been reported. In the present report, a three-point method based on inverse filtering to obtain the radial motion is discussed and the optimal sensor setting angle is calculated based on the transfer function. Furthermore, the proposed method is applied to the radial motion measurement of a spindle for hard disk inspection in the high-revolution range of 4000–10,000 rpm. As a result, the main reason for the radial motion was concluded to be related to the inner or outer ring of the bearing.

Fabrication of Slider-Type Near-Field Arrayed Probe for Optical Data Storage

A near-field optical slider has been prepared for a high-density recording system. The slider includes an array of high-throughput near-field probes and the surface-air bearing of the slider has been designed for a flying height of 20 nm. We have developed a prior-etching process for hollowing out the silicon oxide near-field optical tips. Bottom silicon underneath the arrayed tips and the inner silicon of the tips have been successfully removed for the optical path of visible light.

Recording performance and system integration of perpendicular magnetic recording

Perpendicular recording has been actively developed for future high-density recording system. We studied the integration of the perpendicular recording system to the hard disk drive (HDD). Double layer perpendicular media and single-pole type perpendicular head with GMR reader were employed in 2.5″ HDD. As a result of the integration test, it was confirmed that perpendicular recording 2.5″ test HDDs functioned well at the capacity of 50GB/platter. Through the drive integration, the features of the perpendicular recording were thoroughly studied. The complementary features between perpendicular recording and longitudinal recording are also discussed.

Development of 3-D Read/Write Simulation System for Higher Areal Recording Density

Recently, higher areal recording density of hard disk drive (HDD) is achieved by increasing not only linear density (bits per inch) but also track density (tracks per inch). Then, three-dimensional (3-D) read/write (R/W) simulation is necessary in order to design a high-density recording system by utilizing magnetic field analysis. In this paper, a 3-D R/W simulation system using the edge-based finite-element method (FEM) is developed by introducing the 3-D medium hysteresis model based on the ensemble of the Stoner-Wohlfarth (SW) particles. As it is not easy to apply the Newton-Raphson method for the nonlinear analysis of SW model, an underrelaxation iteration method is used. The effectiveness of the 3-D R/W simulation system is illustrated by applying to the magnetic field analysis of a SPT (single-pole-type) head/DL (double-layer) medium perpendicular recording system.

Design of the Recording Head Considering the Field Gradient in High-Density Magnetic Recording

The gap size of the write head in magnetic recording system is so small compared with full size head, which causes the difficulties in numerical analysis and design. In this paper, a two step of the analysis is presented. After the analysis of the full size head by using conventional three-dimensional finite-element method (FEM), the field gradient of the small gap region is computed by Laplacian analysis. Write field and field gradient of the longitudinal and perpendicular head are to be computed effectively. By using this algorithm, optimum shapes of the write head for high-density recording system could be designed.

Microfabrication of electro- and electroless-deposition and its application in the electronic field

The recent topics of our researches concerned with the electrochemical fabrication process of highly functionalized metal thin films and minute structures are reviewed. We present three topics; the soft magnetic materials of Co alloys by electro- and electroless-plating, the micro-dot formation by Ni electroless deposition, and fabrication of barrier layer on SiO 2 by electroless deposition for ULSI technology. The magnetic property of electrodeposited CoNiFe film was deteriorated by the co-deposition of a small amount of sulfur, whereas the carbon co-deposition improved resistivity of the film. The electroless soft magnetic materials were also proposed for future extremely high-density recording system. As the fine dot formation, the electroless deposition processes for producing fine metal structures were demonstrated. For advanced nano-scale patterning technology, an organic monolayer directly grafted to the Si surface was applied to a novel process of selective metal deposition. Another type of organic monolayer, a self-assembled monolayer of organosilane, was also utilized as an adhesive/catalytic layer for fabrication of a diffusion barrier layer on SiO 2 for future ULSI technology.

Abnormalities of auditory P300 cortical current density in patients with schizophrenia using high density recording

While P300 current density analysis has been performed in schizophrenic patients, the event-related potential data have never been obtained using a high density recording, nor have their cortical images been well demonstrated. In this study, the auditory P300 elicited by an oddball paradigm was recorded using a high density recording system of 128 channels. Thirteen male patients who met DSM-IV criteria for schizophrenia were compared with 20 healthy male controls. The cortical current density analysis of low resolution electromagnetic tomography (LORETA) was applied to the P300 component, and this resulted in the values of 6222 current density points over the surface of a cortex model. The inter-group difference of P300 current density was assessed using a point-by-point comparison by t-test. While the normal controls demonstrated the cortical activation of bilateral frontal, temporal and parietal cortex during the oddball paradigm, visual inspection suggested that in the schizophrenic patients these areas were less activated. The inter-group significance of P300 current density was dominant over the left hemisphere, and particularly over the left prefrontal area. It is concluded that the LORETA current density analysis localizes the neural activity from the cortical fronto-temporo-parietal network as the neural substrates of the scalp recorded P300. The dysfunction of such a network, especially over the left hemisphere, possibly subserves the scalp recorded P300 abnormality in schizophrenia.

Development of a high-density magnetic recording system for a consumer VCR using an MR head

We present a new consumer VCR format, MICROMV, and a higher density recording technique. Applying the MR head to a helical-scan tape recorder, we have successfully recorded at an areal density of 0.8 Gb/in/sup 2/ making it possible to store 6.5 GB of data on a small cassette of 12 cc volume. We also report a technique of electric-power transmission through a rotary drum and a method to compensate for the amplitude asymmetry of the MR head output signal.