Evoked Potentials |
|
 |
|
 |
| Neurophysiological amplifiers and headstages with PowerLab systems may be used to record intracellular and extracellular evoked potentials. |
|
|
|
An evoked potential is a change in membrane potential that is directly induced by an electrical stimulus or the presence of a drug and they are distinct from spontaneous potentials. Evoked potentials are described by their tendency to depolarize (excite) or hyperpolarize (inhibit) the membrane potential and are referred to as excitatory (EPSP) or inhibitory post-synaptic potentials (IPSP). Evoked potentials refer to responses obtained following stimulation of central nervous system structures such as the cerebral cortex, brain stem, spinal cord and peripheral nerves. Evoked potentials include: - Steady-state evoked potentials – when the stimuli are in a rapid succession, the evoked potentials overlap in time until it forms a steady wave
- Motor evoked potentials (MEP) - recorded from muscles following direct stimulation of exposed motor cortex, or magnetic/electrical transcranial stimulation of motor cortex
- Sensory evoked potentials (SEP) - recorded from the central nervous system following stimulation of sense organs
- Visual evoked potentials - generated by a flashing light or changing pattern on a monitor
- Auditory evoked potentials – generated by click or tone stimulus presented through earphones
- Somatosensory evoked potentials (SSEP) - generated by tactile or electrical stimulation of a sensory or mixed nerve in the periphery
Evoked potential amplitudes tend to be low, ranging from less than a microvolt to several microvolts and therefore usually require signal averaging to resolve these low-amplitude potentials against the background of other biological signals and noise. Evoked potentials may be recorded using PowerLab and suitable amplifiers that include intracellular amplifiers manufactured from Dagan Corporation. It must be noted that equipment supplied by Dagan Corporation is NOT suitable for connection to human subjects. These intracellular amplifiers may be used to record IPSP and EPSP signals. For further information, see the:
LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro.
LabChart software is also suitable for evoked potential recordings that do NOT require waveform averaging or if more than two recording channels are required. The triggering option within LabChart is extremely useful to synchronize recordings with a stimulus, while the analog or digital outputs on the PowerLab may be used to control a third-party stimulator. The LabChart software can be used to identify the specific waveform components such as amplitude and latency. LabChart Extensions are free for download from the website for existing LabChart users and they include:
- Event Manager (Win Only): Allows the user to monitor user defined events online using different criteria, and to perform a variety of user defined actions.
- Export Axon (Win Only): Allows the user to save LabChart files in the ABF (Axon binary format) which can be read by pClamp.
- Evoked Response (Mac Only): This extension analyzes physiological responses to a stimulus (evoked response experiments). A number of response parameters can be measured and logged to the Data Pad. This process can be automated to analyze a series of stimuli/response cycles.
- Peak Parameters (Win or Mac): Allows the user to determine a number of parameters for an individual peak. Parameters calculated include peak height, width, slope and various time parameters. It is useful for determining parameters of action potentials such as cardiac potentials, EPSP and IPSP.
- Read Scope (Mac Only): Read Scope is a LabChart extension which allows LabChart for Mac to read Scope for Mac files directly.
- Export Matlab(Win only): Allows LabChart for Windows files to be saved and exported as MATLAB compatible files. MATLAB is a flexible data analysis program available from The Mathworks Inc. (www.mathworks.com).
- Translate Binary (Win only): Translate Binary is a LabChart extension which allows LabChart for Windows files to be saved and exported in a simple binary format. Translate Binary can import documents that have either been exported from LabChart, or generated by another application.
- Translate EDF (Win only): Allows LabChart to save data as an EDF file, and to read EDF files. Translate EDF does not support the EDF+ format.
- Telegraph (Win only): Makes use of the gain-telegraph output from an electrophysiological amplifier to continue to display data at the correct scale after a gain change. The Telegraph Extension uses the gain telegraph voltage from the amplifier to automate the display of electrophysiological data in LabChart, so that the correct units and scale are used.
Scope
Scope software, supplied with PowerLab systems, provides powerful display, recording and analysis features to transform your computer into a two-channel storage oscilloscope, XY plotter or Power Spectrum (FFT) analyser. Scope is used commonly to measure any high-frequency signal that is time-locked to a stimulus such as action potentials and evoked responses. For analyzing Evoked Potentials, the Scope Software is recommended because it provides signal averaging functions that are necessary to extract the evoked response from background noise.
This software:
- Provides the ability to record, display and analyze any high frequency signal that is time-locked to a stimulus
- Synchronizes sweeps with recorded or built-in stimulation patterns
- Provides a range of real-time and offline analysis features
- Generates stimuli of differing intensities and waveform structures (i.e. single-pulse, multiple pulse, simple ramps) and control an external stimulator using the analog output on the front of the PowerLab
Therefore, Scope is an ideal software program for recording any type of evoked potential because each successive stimulus and evoked potential may be recorded in a single sweep and the results of multiple sweeps may be superimposed or averaged to minimize signal noise and isolate the evoked potential. Scope is useful in signal averaging techniques to improve the signal-to-noise ratio and minimize artifacts induced by related events such as the blink-response. Features such as filtering and spectral analysis may be used to identify oscillating potentials. The analog output of the PowerLab data acquisition system may be used to control a stroboscopic flash unit (with suitable inputs) for presentation of the light stimuli.
GLP and 21 CFR Part 11
For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.
Data Recording and AnalysisPowerLab data acquisition systems and LabChart/Scope software are ideal for intracellular recordings due to their ability to record at high sampling rates. The high frequency of neuronal firing rates greatly exceeds the frequency of most other physiological signals. Sampling rates of 40 kHz to 200 kHz are recommended for most intracellular recordings. They include: Intracellular Recording SystemML870B71 Intracellular Recording System includes: Intracellular Preamplifiers and Accessories Stimulators
| Physiological properties of late inspiratory neurons and their possible involvement in inspiratory off-switching in cats |
| A Haji; M Okazaki; H Yamazaki and R Takeda, Journal of Neurophysiology, 1057-1067, 2002 |
| In vagotomized, decerebrate cats the motor output of the central respiratory network was analyzed by recording nerve discharges from the desheathed phrenic nerve through bipolar silver electrodes. Amplified signals (3,00010,000 times) were filtered (303,000 Hz), rectified and integrated with a leaky integrator (time constant, 0.1 s). Membrane potential and discharge properties of late-I neurons in the medulla were recorded either with single micropipettes or with the central micropipette of a six-barrel coaxial array for intracellular recording and extracellular iontophoresis.
All recordings of neuronal activity started were displayed on a computer using signal processing software at a sampling rate of 4,000 Hz and stored on a computer hard disk (Macintosh-PowerLab/4 s; ADInstruments Pty, Castle Hill, Australia).
. Power spectrum analysis of synaptic noise and poststimulus averagings of PSPs were performed using libraries included in PowerLab. For power spectrum analyses, the fast Fourier transform (8,192 points at a sampling rate of 4,000 Hz) was applied to filtered signals (low-pass filter at 250 Hz) occurring during a window of a 2.048-s duration and averaged 15 times. Peak frequency of action potential discharges as well as latency, duration, and amplitude of PSPs were measured.
Recording pipettes were filled with 2 M K-citrate (DC resistance in brain tissue, 3040 MOhms) or 3 M KCl (1015 MOhms).
To determine whether the neurons were vagal or bulbospinal, the occurrence of antidromically conducted action potentials was tested by stimulating the central end of the ipsilateral vagus nerve (0.2- to 0.3-mA intensity, 0.1-ms pulse duration) with bipolar silver electrodes, or the ventrolateral part of the C2C3 spinal cord (0.30.5 mA, 0.2 ms) with an array of five concentric stimulating electrodes. To elicit stimulus evoked IOS responses, a coaxial stimulating electrode was inserted into NPBM (12 mm caudal to the margin of the inferior colliculus, 45 mm lateral to the midline and 23 mm deep from the dorsal surface)
The ipsilateral vagus nerve or NPBM was stimulated by trains of pulses with 1.5 times the threshold intensity (0.20.4 mA) to induce IOS responses. To analyze excitatory postsynaptic potentials (EPSPs) and IPSPs in late-I neurons during the evoked transient inhibition or a premature IOS, single pulses (0.51.0 mA, 0.1 ms) were applied to electrodes in the NPBM or on the vagus nerve
.. Stimulation was delivered at a predetermined time during the respiratory cycle using a triggering pulse derived from the integrated phrenic neurogram. For current injection through the recording pipette into a cell, bridge balance or discontinuous current clamp was used (AxoClamp-2B; Axon Instruments, Foster City, CA). Input resistance was measured by injecting a constant negative current (-1 nA, 100 ms, 2 Hz) through the recording pipette filled with a solution of K-citrate. |
|
| Glycine receptor-mediated inhibition of dopamine and non-dopamine neurons of the rat ventral tegmental area in vitro |
| F Zheng and S V Johnson, Brain Research, 313-317, 2001 |
| Horizontal midbrain slices containing the VTA (300 ΅m) were prepared from adult rats
.. The slice was placed on a nylon mesh in a 0.5-ml recording chamber, immersed and perfused with artificial cerebrospinal fluid
..Intracellular recordings were made using glass microelectrodes filled with either 2 M potassium acetate (KAc) or 2 M potassium chloride (KCl), with tip resistances of 40120 M?. Tips of microelectrodes were positioned in the VTA using a dissecting microscope. Potentials were amplified with an Axoclamp 2A amplifier and recorded using Axotape (IBM-type personal computer) and MacLab chart software (Macintosh computer). Continuously recorded spontaneous inhibitory postsynaptic potentials (IPSPs) were analyzed off-line using Axograph software. |
|
|
|
|
|
|
The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.
|
|
|