Single-unit recording | EPFL Graph Search

In neuroscience, single-unit recordings (also, single-neuron recordings) provide a method of measuring the electro-physiological responses of a single neuron using a microelectrode system. When a neuron generates an action potential, the signal propagates down the neuron as a current which flows in and out of the cell through excitable membrane regions in the soma and axon. A microelectrode is inserted into the brain, where it can record the rate of change in voltage with respect to time. These microelectrodes must be fine-tipped, impedance matching; they are primarily glass micro-pipettes, metal microelectrodes made of platinum, tungsten, iridium or even iridium oxide. Microelectrodes can be carefully placed close to the cell membrane, allowing the ability to record extracellularly. Single-unit recordings are widely used in cognitive science, where it permits the analysis of human cognition and cortical mapping. This information can then be applied to brain–machine interface (BMI)

Large-scale, high-resolution electrophysiological imaging of field potentials in brain slices with microelectronic multielectrode arrays

Luca Berdondini, Diego Ghezzi

Multielectrode arrays (MEAs) are extensively used for electrophysiological studies on brain slices, but the spatial resolution and field of recording of conventional arrays are limited by the low number of electrodes available. Here, we present a large-scale array recording simultaneously from 4096 electrodes used to study propagating spontaneous and evoked network activity in acute murine cortico-hippocampal brain slices at unprecedented spatial and temporal resolution. We demonstrate that multiple chemically induced epileptiform episodes in the mouse cortex and hippocampus can be classified according to their spatio-temporal dynamics. Additionally, the large-scale and high-density features of our recording system enable the topological localization and quantification of the effects of antiepileptic drugs in local neuronal microcircuits, based on the distinct field potential propagation patterns. This novel high-resolution approach paves the way to detailed electrophysiological studies in brain circuits spanning spatial scales from single neurons up to the entire slice network.

Frontiers Research Foundation2012

Implantable Autonomous Wireless Closed-loop Bio-electronics for Epilepsy Control

Reza Ranjandish

Implantable electronic medical device (IEMD) is an emerging technology that plays an important role in the treatment of several neurological disorders such as epilepsy, especially in the cases of drug-resistant epilepsy. Recent developments and studies show the possibility of accurate detection of seizure onset and stopping the seizures or shortening their duration using electrical neural stimulation. By employing these devices, the quality of the life of the patients who could not benefit from anti-epileptic medicines or surgery will improve, significantly. An IEMD uses a neural recording interface to sense and amplify neural signals. Increasing the number of recording channels from few recording channels to hundreds is a promising feature of the future IEMDs. However, employing hundreds of recording channels brings several challenges including minimizing the power consumption which relates to the temperature elevation in the device and may damage the tissues around the IEMD. In order to implement a low-power implantable electronic device for neural recording, epilepsy detection and epilepsy control with a high spatiotemporal resolution, some techniques should be devised to solve this issue. Closed-loop implantable electronics is a new trend for controlling seizures by detecting them and applying an electrical stimulation to the brain or a group of nerves. These devices employ electrical stimulators; however, electrical stimulation requires very careful consideration due to the safety issues. A poor design of the electrical stimulator may damage the brain tissue and endanger the life of the patients. Hence, charge balancers are introduced to ensure the safety of the electrical stimulation. In addition, closed-loop implantable devices for seizure control require an accurate seizure onset detector. These devices should detects all the seizures with the least latency to stop the seizures or stop them to spread in the brain. The first part of this thesis presents a low-power and compact size seizure detection system while discussing the challenges in the design of neural amplifiesr, feature extractors and data compression circuits. Then a comprehensive study on electrical stimulation and charge balancing are provided. Consequently, circuit techniques to achieve a low-power, low-are and accurate charge balancers are present. Finally, a neural recording system based on orthogonal sampling and two closed-loop stimulation systems for epilepsy control are proposed. Orthogonal sampling enables reducing the number of the ADCs in conventional recording systems into one single unit while simultaneously recording from several channels. Consequently, the ADC bandwidth and dynamic range is effectively employed and shared between all the channels without any loss in the temporal information of the channels during sampling, which is not the case of time-multiplexed ADCs. In an IoT based closed-loop stimulation system for epilepsy control, the system is divided into two parts including implantable part and external parts. Using wearable devices, several biomarkers are recorded and sent to the implantable part of the system to improve the accuracy of the detection. In the end, an all wireless implantable closed-loop stimulation system is presented with an accurate charge balanced stimulator.

EPFL2019

Light-Evoked Modulation of Neuronal Activity with Conjugated Polymers

Diego Ghezzi, Mattia Nova

Organic bioelectronics aims at the intimate integration between organic materials and biological tissues in order to obtain a targeted functional outcome. In the last decades, conductive polymers have been successfully employed to interface excitable cells through biocompatible probes and devices. We previously reported the possibility to culture primary neurons on photosensitive conjugated polymers, such as poly(3-hexylthiophene) (P3HT), without altering either the polymer or the neuronal properties. These neurons displayed a depolarizing response to a brief (< 50 ms) green light stimulus and a consequent control over the action potential firing rate. The same interface was also shown to elicit activation of retinal circuitry and ganglion cell firing in explanted degenerate retinas upon light stimulation. However, while neuronal excitation has been extensively proved via planar or protruding electrodes, carbon nanotubes, and conjugated polymers, the hyperpolarization of neurons and silencing of their firing activity has been achieved with optogenetics, but rarely documented for functionalized planar devices and structures. We show here a method to induce both depolarization and hyperpolarization of cells interfaced with conjugated polymers upon prolonged (500 ms) light stimulation. Patch-clamp experiments showed that HEK293 cells grown on P3HT displayed a biphasic response composed of an initial depolarization followed by a sustained hyperpolarization during light illumination. We also documented that the amplitude of the light-induced hyperpolarization was reduced in the absence of intracellular potassium, but was insensitive to changes in the intracellular chloride concentration. A prolonged illumination was equally able to hyperpolarize primary neurons cultured over P3HT and significantly reduced both spontaneous and electrically elicited action potential frequency. We further assessed the translatability of our findings to tissue stimulation by describing the modulation of ganglion cell firing in explanted blind retinas from Royal College of Surgeons rats, a model of Retinitis pigmentosa. By coupling conjugated polymers with multi-electrode arrays and conventional metal electrodes, single-unit activity of ganglion cells was inhibited by prolonged illumination. We similarly investigated the phenomenon in acute hippocampal brain slices placed onto a conjugated polymer thin film. These results indicate that conjugated polymers can be used to non-invasively excite and inhibit the electrical activity of cells cultured on its surface. Furthermore, the translation of our findings from in vitro cultures to different central nervous system tissues, suggests a potential application of these organic devices as a tool for modulation of neuronal activity in vivo.

2015