[Show abstract][Hide abstract] ABSTRACT: One of the most difficult tasks for the surgeon during the removal of low-grade gliomas is to identify as precisely as possible the borders between functional and non-functional brain tissue with the aim of obtaining the maximal possible resection which allows to the patient the longer survival. For this purpose, systems for acute extracellular recordings of single neuron and multi-unit activity are considered promising. Here we describe a system to be used with 16 microelectrodes arrays that consists of an autoclavable headstage, a built-in inserter for precise electrode positioning and a system that measures and controls the pressure exerted by the headstage on the brain with a twofold purpose: to increase recording stability and to avoid disturbance of local perfusion which would cause a degradation of the quality of the recording and, eventually, local ischemia. With respect to devices where only electrodes are autoclavable, our design permits the reduction of noise arising from long cable connections preserving at the same time the flexibility and avoiding long-lasting gas sterilization procedures. Finally, size is much smaller and set up time much shorter compared to commercial systems currently in use in surgery rooms, making it easy to consider our system very useful for intra-operatory mapping operations.
IEEE Transactions on Biomedical Circuits and Systems 06/2014; · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The concept of a brain-machine interface (BMI) or a computer-brain interface is simple: BMI creates a communication pathway for a direct control by brain of an external device. In reality BMIs are very complex devices and only recently the increase in computing power of microprocessors enabled a boom in BMI research that continues almost unabated to this date, the high point being the insertion of electrode arrays into the brains of 5 human patients in a clinical trial run by Cyberkinetics with few other clinical tests still in progress. Meanwhile several EEG-based BMI devices (non-invasive BMIs) were launched commercially. Modern electronics and dry electrode technology made possible to drive the cost of some of these devices below few hundred dollars. However, the initial excitement of the direct control by brain waves of a computer or other equipment is dampened by large efforts required for learning, high error rates and slow response speed. All these problems are directly related to low information transfer rates typical for such EEG-based BMIs. In invasive BMIs employing multiple electrodes inserted into the brain one may expect much higher information transfer rates than in EEG-based BMIs because, in theory, each electrode provides an independent information channel. However, although invasive BMIs require more expensive equipment and have ethical problems related to the need to insert electrodes in the live brain, such financial and ethical costs are often not offset by a dramatic improvement in the information transfer rate. Thus the main topic of this review is why in invasive BMIs an apparently much larger information content obtained with multiple extracellular electrodes does not translate into much higher rates of information transfer? This paper explores possible answers to this question by concluding that more research on what movement parameters are encoded by neurons in motor cortex is needed before we can enjoy the next generation BMIs.
[Show abstract][Hide abstract] ABSTRACT: This paper reports a multi-channel neural spike recording system-on-chip with digital data compression and wireless telemetry. The circuit consists of 16 amplifiers, an analog time-division multiplexer, a single 8 bit analog-to-digital converter, a digital signal compression unit and a wireless transmitter. Although only 16 amplifiers are integrated in our current die version, the whole system is designed to work with 64, demonstrating the feasibility of a digital processing and narrowband wireless transmission of 64 neural recording channels. Compression of the raw data is achieved by detecting the action potentials (APs) and storing 20 samples for each spike waveform. This compression method retains sufficiently high data quality to allow for single neuron identification (spike sorting). The 400 MHz transmitter employs a Manchester-Coded Frequency Shift Keying (MC-FSK) modulator with low modulation index. In this way, a 1.25 Mbit/s data rate is delivered within a limited band of about 3 MHz. The chip is realized in a 0.35 µm AMS CMOS process featuring a 3 V power supply with an area of 3.1 × 2.7 mm 2 . The achieved transmission range is over 10 m with an overall power consumption for 64 channels of 17.2 mW. This figure translates into a power budget of 269 µW per channel, in line with published results but allowing a larger transmission distance and more efficient bandwidth occupation of the wireless link. The integrated circuit was mounted on a small and light board to be used J. Low Power Electron. Appl. 2012, 2 212 during neuroscience experiments with freely-behaving rats. Powered by 2 AAA batteries, the system can continuously work for more than 100 hours allowing for long-lasting neural spike recordings.
Journal of Low Power Electronics and Applications. 09/2012; 2(4):211-241.
[Show abstract][Hide abstract] ABSTRACT: Although the firing patterns of collision-detecting neurons have been described in detail in several species, the mechanisms generating responses in these neurons to visual objects on a collision course remain largely unknown. This is partly due to the limited number of intracellular recordings from such neurons, particularly in vertebrate species. By employing patch recordings in a novel integrated frog eye-tectum preparation we tested the hypothesis that OFF retinal ganglion cells were driving the responses to visual objects on a collision course in the frog optic tectum neurons. We found that the majority (22/26) of neurons in layer 6 responding to visual stimuli fitted the definition of η class collision-detectors: they readily responded to a looming stimulus imitating collision but not a receding stimulus (spike count difference ∼10 times) and the spike firing rate peaked after the stimulus visual angle reached a threshold value of ∼20-45°. In the majority of these neurons (15/22) a slow frequency oscillation (f=∼20Hz) of the neuronal membrane potential could be detected in the responses to a simulated collision stimulus, as well as to turning off the lights. Since OFF retinal ganglion cells could produce such oscillations, our observations are in agreement with the hypothesis that 'collision' responses in the frog optic tectum neurons are driven by synaptic inputs from OFF retinal ganglion cells.
[Show abstract][Hide abstract] ABSTRACT: It has been noted that the power spectrum of intracortical local field potential (LFP) often scales as 1/f(-2). It is thought that LFP mostly represents the spiking-related neuronal activity such as synaptic currents and spikes in the vicinity of the recording electrode, but no 1/f(2) scaling is detected in the spike power. Although tissue filtering or modulation of spiking activity by UP and DOWN states could account for the observed LFP scaling, there is no consensus as to how it arises. We addressed this question by recording simultaneously LFP and single neurons ("single units") from multiple sites in somatosensory cortex of anesthetized rats. Single-unit data revealed the presence of periods of high activity, presumably corresponding to the "UP" states when the neuronal membrane potential is depolarized, and periods of no activity, the putative "DOWN" states when the membrane potential is close to resting. As expected, the LFP power scaled as 1/f(2) but no such scaling was found in the power spectrum of spiking activity. Our analysis showed that 1/f(2) scaling in the LFP power spectrum was largely generated by the steplike transitions between UP and DOWN states. The shape of the LFP signal during these transitions, but not the transition timing, was crucial to obtain the observed scaling. These transitions were probably induced by synchronous changes in the membrane potential across neurons. We conclude that a 1/f(2) scaling in the LFP power indicates the presence of steplike transitions in the LFP trace and says little about the statistical properties of the associated neuronal firing.
Journal of Neurophysiology 11/2011; 107(3):984-94. · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Extracellular metal microelectrodes are widely used to record single neuron activity in vivo. However, their signal-to-noise ratio (SNR) is often far from optimal due to their high impedance value. It has been recently reported that carbon nanotube (CNT) coatings may decrease microelectrode impedance, thus improving their performance. To tease out the different contributions to SNR of CNT-coated microelectrodes we carried out impedance and noise spectroscopy measurements of platinum/tungsten microelectrodes coated with a polypyrrole-CNT composite. Neuronal signals were recorded in vivo from rat cortex by employing tetrodes with two recording sites coated with polypyrrole-CNT and the remaining two left untreated. We found that polypyrrole-CNT coating significantly reduced the microelectrode impedance at all neuronal signal frequencies (from 1 to 10 000 Hz) and induced a significant improvement of the SNR, up to fourfold on average, in the 150-1500 Hz frequency range, largely corresponding to the multiunit frequency band. An equivalent circuit, previously proposed for porous conducting polymer coatings, reproduced the impedance spectra of our coated electrodes but could not explain the frequency dependence of SNR improvement following polypyrrole-CNT coating. This implies that neither the neural signal amplitude, as recorded by a CNT-coated metal microelectrode, nor noise can be fully described by the equivalent circuit model we used here and suggests that a more detailed approach may be needed to better understand the signal propagation at the electrode-solution interface. Finally, the presence of significant noise components that are neither thermal nor electronic makes it difficult to establish a direct relationship between the actual electrode noise and the impedance spectra.
Journal of Neural Engineering 11/2011; 8(6):066013. · 3.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The paper describes a multi-channel neural spike recording system sensing and processing the action potentials (APs) detected by an electrode array implanted in the cortex of freely-behaving small laboratory animals. The core of the system is a custom integrated circuit (IC), with low-noise analog front-end interfaced to a 16 electrode array followed by a single 8-bit SAR ADC, a digital signal compression and a 400-MHz wireless transmission units. Data compression is implemented by detecting action potentials and storing up to 20 points per each spike waveform. The choice greatly improves data quality and allows single spike identification. The transmitter delivers a 1.25-Mbit/s data rate coded with a Manchester-coded frequency shift keying (MC-FSK) within a 3-MHz bandwidth. An overall power consumption of 17.2mW makes possible to reach a transmission range larger than 20-m. The IC is mounted on a small and light printed circuit board. Two AAA batteries, set in a pack positioned on the back of the animal, power the system that can work continuously for more than 100h.
[Show abstract][Hide abstract] ABSTRACT: This paper reports a multi-channel neural recording system-on-chip (SoC) with digital data compression and wireless telemetry. The circuit consists of a 16 amplifiers, an analog time division multiplexer, an 8-bit SAR AD converter, a digital signal processor (DSP) and a wireless narrowband 400-MHz binary FSK transmitter. Even though only 16 amplifiers are present in our current die version, the whole system is designed to work with 64 channels demonstrating the feasibility of a digital processing and narrowband wireless transmission of 64 neural recording channels. A digital data compression, based on the detection of action potentials and storage of correspondent waveforms, allows the use of a 1.25-Mbit/s binary FSK wireless transmission. This moderate bit-rate and a low frequency deviation, Manchester-coded modulation are crucial for exploiting a narrowband wireless link and an efficient embeddable antenna. The chip is realized in a 0.35- εm CMOS process with a power consumption of 105 εW per channel (269 εW per channel with an extended transmission range of 4 m) and an area of 3.1 × 2.7 mm(2). The transmitted signal is captured by a digital TV tuner and demodulated by a wideband phase-locked loop (PLL), and then sent to a PC via an FPGA module. The system has been tested for electrical specifications and its functionality verified in in-vivo neural recording experiments.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:1555-60.
[Show abstract][Hide abstract] ABSTRACT: Since the proof of viability of prosthetic devices directly controlled by neurons, there is a huge increase in the interest on integrated multichannel recording systems to register neural signals with implanted chronic electrodes. One of the bottlenecks in such compact systems is the limited rate of data transmission by the wireless link, requiring some sort of data compression/reduction. We propose an analog low power integrated system for action potential (AP) detection and sorting that reduces the output data rate ~100 times. In this system, AP detection is performed by a double threshold method that reduces the probability of false detections while AP sorting is based on the measurement of peak and trough amplitudes and peak width. The circuit has been implemented in 0.35 - mum CMOS technology with power consumption of 70 muW per channel including the pre-amplifier. The system was tested with real recorded traces: compared to standard AP sorting techniques, the proposed simple AP sorter was able to correctly assign to single units over 90% of detected APs.
Biomedical Circuits and Systems Conference, 2008. BioCAS 2008. IEEE; 12/2008
[Show abstract][Hide abstract] ABSTRACT: We present a 64-channels IC front-end for implantable systems using extracellular neural signals for rehabilitation purposes. Each channel of the ASIC consists of a high-pass filter with subthreshold feedback resistance and a line buffer. Channels are scanned through a time-division multiplexer followed by a variable gain amplifier and an output buffer. Power consumption is 500 muW per channel with plusmn1.65 V dual supply and an excellent noise performance of 2.9 muVrms (100 Hz- 10 kHz).
Solid State Circuits Conference, 2007. ESSCIRC 2007. 33rd European; 10/2007
[Show abstract][Hide abstract] ABSTRACT: A number of spike detection and sorting methods exist and the availability of powerful desktop computers may suggest that the problem of spike detection is solved. However, for portable multi-channel systems, when one takes into account the power consumption limitations, computationally simple methods can be advantageous when compared to more complex algorithms. Here we describe a simple spike detection method that reduces approximately two-fold the rate of false detections compared to the single threshold spike detection method. The proposed algorithm can be employed in an analog electronic chip thus eliminating the need for the digitization of the original signal. Consequently, only the times of spike occurrence can be transmitted for further analysis.
Journal of Neuroscience Methods 06/2007; 163(1):176-80. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An increasing popularity of multichannel recordings from freely behaving animals and the need to develop a practical brain-machine interface has fuelled the development of miniature multichannel recording systems. Here we describe our prototype miniature 64-channel acquisition system that could be used for multichannel recordings in freely behaving monkeys or other large animals. The system's features include an high impedance input for neurophysiology electrodes, an integrated battery fed circuitry with a 64 low-noise multiplexed amplifiers array that permits the parallel recording of all channels, a 10-bit resolution ADC, an FPGA digital core for online processing and data transmission, a USB 2.0 link and a custom software for data visualization and whole system control.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:441-4.
[Show abstract][Hide abstract] ABSTRACT: For extracellular recordings from neurons, it is desirable to use the same electrode for stimulation as well as for recording. Since neural preamplifiers usually exhibit high-pass filtering at frequencies as low as 0.1 Hz, the recovery from saturation is typically very slow. Consequently, following stimulation, no signal can be detected for up to several seconds. This is unacceptably slow response of the preamplifier because the majority of neurons fires action potentials within first milliseconds following stimulation. Here we propose to use a switched-capacitor preamplifier with adjustable pass-band for fast recovery from saturation caused by stimulation via the recording electrode. The idea was tested in a real preamplifier manufactured with a standard CMOS technology (0.35 microm). In control conditions, the high-pass filter was set to 100 Hz and, during stimulation, was shifted to 10 kHz. Such a shift allows the reduction of the recovery time from tens of milliseconds to sub-millisecond range.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:652-5.
[Show abstract][Hide abstract] ABSTRACT: There is increasing interest in the development of small hybrid cell-semiconductor systems for the non-invasive evaluation of the physiological state of a cell population. These miniature devices can be used in many areas of biomedical applications, ranging from basic research to drug screening during cancer chemosensitivity testing in clinics. A prerequisite for the biological and medical application of these devices is that cells retain their functional and growth properties when in contact with the semiconductor sensor material. The sensor surface is usually coated with dielectric silicon dioxide (SiO2 ) or a silicon nitride layer (Si3 N4 ); therefore, cellular adhesion to these materials and cellular viability on these surfaces are of crucial im-portance. This is especially true for bone cells that are sensitive to the surface microstructure. Therefore, we investigated the short-term (1-7 days) behavior of model bone cells (MG63 human osteosarcoma cells) grown on silicon samples coated with SiO2 . Cell adhesion and morphology were evaluated by scanning electron microscopy (SEM) 1 day after seeding and cell pro-liferation was evaluated by Alamar Blue assay at 2, 3 and 7 days after seeding. No adverse cellular reactions could be detected with these assays suggesting that the tested substrate is suitable for the hybrid cell-semiconductor systems that test bone tumor chemosensitivity.
[Show abstract][Hide abstract] ABSTRACT: In the last decade, a number of laboratories have developed devices that combine electronic components with living cells, including neurons. These devices can be used as cell-based biosensors or labs-on-a-chip for testing of the tumor cell sensitivity to anti-cancer drugs, detection of toxins and chemical substances and pre-clinical evaluation of new drugs. Here we review briefly the existing types of the cell-based biosensors and the strategies employed to improve these complex devices. We argue that, for the neuron-based biosensors, introduction of structure in the connections of the synaptic network should significantly improve the utility of such devices.