8
Stimulation Using Planar Microelectrodes
The MED64 Head Amplifier has a built-in 2 channel current-driven stimulator that enables stimulation via any of
the 64 electrodes. The stimulus current amplitudes and channels are set in the [Acquire MED64R2 Data w/Stim]
module in the MED64 Mobius software. Please refer to the Mobius Tutorial for setting up the stimulation
parameters.
Fig.4 shows a schematic diagram of the extracellular electrical stimulation circuit for the MED64 system. The
stimulus current flows from the selected electrode to reference electrodes. The applied stimulus current charges
the “electrical double-layer capacitor” (Ce) at the interface of electrode, subsequently changing the Ce voltage
(Vc). This current modulates the field potential, which results in hyperpolarization or depolarization of cellular
membranes. The field potentials (Vf) change according to the output current (Is) as seen on the right in the
Fig.4.
Stimulus Artifacts and Biphasic Stimulation
During stimulation, signals (stimulus pulses) are recorded at recording channels (non-stimulated channels) due
to crosstalk, causing "stimulus artifacts”. These stimulus artifacts can persist even after the stimulus pulse
returns to zero and can interfere with the recording of real biological signals.
This is mainly due to following factors:
Fig.3.
Mobius’ Control panel for setting stimulus parameter.
Select stimulator
Set
Select stimulus electrode
s
stimulus waveform
Ce: Capacitance of electrical double-layer capacitor (electrode)
Re: Resistance of electrode
Rs: Resistance of solution with slice
Is: Stimulator output current
Vs: Stimulator output voltage
Vc: Voltage of Ce
Vf: Voltage of Rs (Voltage change in the field)
Stimulator output
current (Is)
Stimulator output
voltage (Vs)
Voltage of Ce (Vc)
Voltage of Rs (Vf)
(Changes in the
field potentials)
Fig.4
. Stimulation using microelectrodes at the MED64 system.
