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A long-lasting wireless stimulator for small mammals.

Hentall ID - Front Neuroeng (2013)

Bottom Line: The chronic effects of electrical stimulation in unrestrained awake rodents are best studied with a wireless neural stimulator that can operate unsupervised for several weeks or more.Microstimulation of the rat's raphe nuclei with intermittent 5-min (50% duty cycle) trains of 30 μA, 1 ms pulses at 8 or 24 Hz frequency during 12 daylight hours lasted 21.1 days ±0.8 (mean ± standard error, Kaplan-Meir censored estimate, n = 128).Devices with these general features can address in small mammals many of the biological and technical questions arising neurosurgically with prolonged peripheral or deep brain stimulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological Surgery and The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami Miami, FL, USA.

ABSTRACT
The chronic effects of electrical stimulation in unrestrained awake rodents are best studied with a wireless neural stimulator that can operate unsupervised for several weeks or more. A robust, inexpensive, easily built, cranially implantable stimulator was developed to explore the restorative effects of brainstem stimulation after neurotrauma. Its connectorless electrodes directly protrude from a cuboid epoxy capsule containing all circuitry and power sources. This physical arrangement prevents fluid leaks or wire breakage and also simplifies and speeds implantation. Constant-current pulses of high compliance (34 volts) are delivered from a step-up voltage regulator under microprocessor control. A slowly pulsed magnetic field controls activation state and stimulation parameters. Program status is signaled to a remote reader by interval-modulated infrared pulses. Capsule size is limited by the two batteries. Silver oxide batteries rated at 8 mA-h were used routinely in 8 mm wide, 15 mm long and 4 mm high capsules. Devices of smaller contact area (5 by 12 mm) but taller (6 mm) were created for mice. Microstimulation of the rat's raphe nuclei with intermittent 5-min (50% duty cycle) trains of 30 μA, 1 ms pulses at 8 or 24 Hz frequency during 12 daylight hours lasted 21.1 days ±0.8 (mean ± standard error, Kaplan-Meir censored estimate, n = 128). Extended lifetimes (>6 weeks, no failures, n = 16) were achieved with larger batteries (44 mA-h) in longer (18 mm), taller (6 mm) capsules. The circuit and electrode design are versatile; simple modifications allowed durable constant-voltage stimulation of the rat's sciatic nerve through a cylindrical cathode from a subcutaneous pelvic capsule. Devices with these general features can address in small mammals many of the biological and technical questions arising neurosurgically with prolonged peripheral or deep brain stimulation.

No MeSH data available.


Related in: MedlinePlus

Ex vivo testing. (A) The stimulus current measured at 5 different stimulus amplitudes. (B) External signaling pulses sent during the highest amplitude current. The pattern alternated between (B1) and (B2) during the active stimulation phase. The first pulse interval in (B1) represents stimulus width plus clock time and the second represents stimulus amplitude; the first interval in (B2) represents pulse width and the second represents clock time plus amplitude. The alternation allows more than two parameters to be encoded with two intervals, to reduce power usage while transmitting at a reasonably fast update rate to the external reader. Inactive phases were signaled by the presence of four pulses, so there was no alternation of pattern. (C) Control voltages delivered during the stimulus pulses of graph (A). All graphs have the same time base.
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Figure 2: Ex vivo testing. (A) The stimulus current measured at 5 different stimulus amplitudes. (B) External signaling pulses sent during the highest amplitude current. The pattern alternated between (B1) and (B2) during the active stimulation phase. The first pulse interval in (B1) represents stimulus width plus clock time and the second represents stimulus amplitude; the first interval in (B2) represents pulse width and the second represents clock time plus amplitude. The alternation allows more than two parameters to be encoded with two intervals, to reduce power usage while transmitting at a reasonably fast update rate to the external reader. Inactive phases were signaled by the presence of four pulses, so there was no alternation of pattern. (C) Control voltages delivered during the stimulus pulses of graph (A). All graphs have the same time base.

Mentions: A magnetic reed switch (Coto Technology, CT05-1535-J1) serves as the transducer for remote control of stimulator settings. It passes no current when open and, given a suitably high value of in-series resistor, passes very low current when closed. Wireless output is signaled by an infrared (IR) light-emitting diode (Everlight Electronics Co. IR91-21C), using a customized pulse-interval code of 3 or 4 brief (20 μs) pulses. The current delivered by the LT3464 voltage regulator is set by a resistor (R2) attached to the FB pin (Figure 1A). The internal chip design provides the options of constant output when the voltage at the CTRL pin is >1.25 V or variable output when it is <1.25 V (Shtartgot, 2003). A roughly tenfold range of voltages is achievable for a fixed value of R2, from 34 V maximum to a minimum near the battery power supply. Most experiments using the fixed mode set the amplitude at 30 μA. Experiments that called for higher currents used the variable mode, with output programmed in 5 steps up to 100 μA (Figure 2C). The analog control voltage (0–1 V) is created by pulse-width modulation (PWM) of one of the microprocessor's output pins with an RC time-constant of 0.47 ms. Digital-to-analog (DAC) conversion by PWM minimizes the required size and number of components, compared with DAC or digital potentiometer ICs, for example. The CTRL pin also feeds the gate of an FET switch (Q1 in Figure 1A), which is closed by a higher voltage (>1.5 V), serving to truncate the otherwise slow output decay of the LT3464 step-up regulator after shutdown.


A long-lasting wireless stimulator for small mammals.

Hentall ID - Front Neuroeng (2013)

Ex vivo testing. (A) The stimulus current measured at 5 different stimulus amplitudes. (B) External signaling pulses sent during the highest amplitude current. The pattern alternated between (B1) and (B2) during the active stimulation phase. The first pulse interval in (B1) represents stimulus width plus clock time and the second represents stimulus amplitude; the first interval in (B2) represents pulse width and the second represents clock time plus amplitude. The alternation allows more than two parameters to be encoded with two intervals, to reduce power usage while transmitting at a reasonably fast update rate to the external reader. Inactive phases were signaled by the presence of four pulses, so there was no alternation of pattern. (C) Control voltages delivered during the stimulus pulses of graph (A). All graphs have the same time base.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3795361&req=5

Figure 2: Ex vivo testing. (A) The stimulus current measured at 5 different stimulus amplitudes. (B) External signaling pulses sent during the highest amplitude current. The pattern alternated between (B1) and (B2) during the active stimulation phase. The first pulse interval in (B1) represents stimulus width plus clock time and the second represents stimulus amplitude; the first interval in (B2) represents pulse width and the second represents clock time plus amplitude. The alternation allows more than two parameters to be encoded with two intervals, to reduce power usage while transmitting at a reasonably fast update rate to the external reader. Inactive phases were signaled by the presence of four pulses, so there was no alternation of pattern. (C) Control voltages delivered during the stimulus pulses of graph (A). All graphs have the same time base.
Mentions: A magnetic reed switch (Coto Technology, CT05-1535-J1) serves as the transducer for remote control of stimulator settings. It passes no current when open and, given a suitably high value of in-series resistor, passes very low current when closed. Wireless output is signaled by an infrared (IR) light-emitting diode (Everlight Electronics Co. IR91-21C), using a customized pulse-interval code of 3 or 4 brief (20 μs) pulses. The current delivered by the LT3464 voltage regulator is set by a resistor (R2) attached to the FB pin (Figure 1A). The internal chip design provides the options of constant output when the voltage at the CTRL pin is >1.25 V or variable output when it is <1.25 V (Shtartgot, 2003). A roughly tenfold range of voltages is achievable for a fixed value of R2, from 34 V maximum to a minimum near the battery power supply. Most experiments using the fixed mode set the amplitude at 30 μA. Experiments that called for higher currents used the variable mode, with output programmed in 5 steps up to 100 μA (Figure 2C). The analog control voltage (0–1 V) is created by pulse-width modulation (PWM) of one of the microprocessor's output pins with an RC time-constant of 0.47 ms. Digital-to-analog (DAC) conversion by PWM minimizes the required size and number of components, compared with DAC or digital potentiometer ICs, for example. The CTRL pin also feeds the gate of an FET switch (Q1 in Figure 1A), which is closed by a higher voltage (>1.5 V), serving to truncate the otherwise slow output decay of the LT3464 step-up regulator after shutdown.

Bottom Line: The chronic effects of electrical stimulation in unrestrained awake rodents are best studied with a wireless neural stimulator that can operate unsupervised for several weeks or more.Microstimulation of the rat's raphe nuclei with intermittent 5-min (50% duty cycle) trains of 30 μA, 1 ms pulses at 8 or 24 Hz frequency during 12 daylight hours lasted 21.1 days ±0.8 (mean ± standard error, Kaplan-Meir censored estimate, n = 128).Devices with these general features can address in small mammals many of the biological and technical questions arising neurosurgically with prolonged peripheral or deep brain stimulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurological Surgery and The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami Miami, FL, USA.

ABSTRACT
The chronic effects of electrical stimulation in unrestrained awake rodents are best studied with a wireless neural stimulator that can operate unsupervised for several weeks or more. A robust, inexpensive, easily built, cranially implantable stimulator was developed to explore the restorative effects of brainstem stimulation after neurotrauma. Its connectorless electrodes directly protrude from a cuboid epoxy capsule containing all circuitry and power sources. This physical arrangement prevents fluid leaks or wire breakage and also simplifies and speeds implantation. Constant-current pulses of high compliance (34 volts) are delivered from a step-up voltage regulator under microprocessor control. A slowly pulsed magnetic field controls activation state and stimulation parameters. Program status is signaled to a remote reader by interval-modulated infrared pulses. Capsule size is limited by the two batteries. Silver oxide batteries rated at 8 mA-h were used routinely in 8 mm wide, 15 mm long and 4 mm high capsules. Devices of smaller contact area (5 by 12 mm) but taller (6 mm) were created for mice. Microstimulation of the rat's raphe nuclei with intermittent 5-min (50% duty cycle) trains of 30 μA, 1 ms pulses at 8 or 24 Hz frequency during 12 daylight hours lasted 21.1 days ±0.8 (mean ± standard error, Kaplan-Meir censored estimate, n = 128). Extended lifetimes (>6 weeks, no failures, n = 16) were achieved with larger batteries (44 mA-h) in longer (18 mm), taller (6 mm) capsules. The circuit and electrode design are versatile; simple modifications allowed durable constant-voltage stimulation of the rat's sciatic nerve through a cylindrical cathode from a subcutaneous pelvic capsule. Devices with these general features can address in small mammals many of the biological and technical questions arising neurosurgically with prolonged peripheral or deep brain stimulation.

No MeSH data available.


Related in: MedlinePlus