Circuit Models and Experimental Noise Measurements of Micropipette Amplifiers for Extracellular Neural Recordings from Live Animals

Abstract

Glass micropipettes are widely used to record neural activity from single neurons or clusters of neurons extracellularly in live animals. However, to date, there has been no comprehensive study of noise in extracellular recordings with glass micropipettes. The purpose of this work was to assess various noise sources that affect extracellular recordings and to create model systems in which novel micropipette neural amplifier designs can be tested. An equivalent circuit of the glass micropipette and the noise model of this circuit, which accurately describe the various noise sources involved in extracellular recordings, have been developed. Measurement schemes using dead brain tissue as well as extracellular recordings from neurons in the inferior colliculus, an auditory brain nucleus of an anesthetized gerbil, were used to characterize noise performance and amplification efficacy of the proposed micropipette neural amplifier. According to our model, the major noise sources which influence the signal to noise ratio are the intrinsic noise of the neural amplifier and the thermal noise from distributed pipette resistance. These two types of noise were calculated and measured and were shown to be the dominating sources of background noise for in vivo experiments.

An Integrated Circuit for Simultaneous Extracellular Electrophysiology Recording and Optogenetic Neural Manipulation

“…The noise model in Fig. 1 was expanded from our previously model in which a glass pipette electrode was used and without noises arisen from optogenetic control [44]. …”

“…[44]. In short, a 1 Vpp sinusoidal voltage with a sweeping frequency from 1 to 5000 Hz was connected to a 10 MΩ resistor and the neural amplifier in series.…”

“…The role of the amplifier’s input impedance, which is one of the important parameters for extracellular recordings, has not received much attention in these designs. Tailoring the input impedances of the amplifiers allows for selective measurements of local filed potentials, action potentials from multiple neurons, or action potentials from a single neuron [29], [44]. In particular, a high impedance electrode with a small recording surface is necessary to record single neuronal activity and designs of neural amplifiers specially tailored for this application are relatively few.…”

Low-latency single channel real-time neural spike sorting system based on template matching

“…Recording action potentials from neurons in the brain gives neuroscientists the ability to study neural circuits with single cell accuracy [1–6] Typically neural spikes (or action potentials) are recorded extracellularly with a metal or glass electrode inserted into the brain of an animal or a human patient [7,8]. By contrast, intracellular or patch clamp recordings with glass pipettes are much less common in vivo because pulsation, movement of brain tissue and electrode contamination make them very challenging.…”

“…The underlying principle of spike sorting relies on the fact that neural spikes originating from different neurons will have different temporal profiles. The temporal profiles of these neural spikes are dependent on the impedance of the extracellular fluid between the neurons and the electrode, the currents produced by each neuron, as well as the cell membrane area from which the ionic currents can reach the metal electrode [1,7,8].…”