ABSTRACT
Objective.Detection of the epileptogenic zone is critical, especially for patients with drug-resistant epilepsy. Accurately mapping cortical regions exhibiting high activity during spontaneous seizure events while detecting neural activity up to 500 Hz can assist clinicians' surgical decisions and improve patient outcomes.Approach.We designed, fabricated, and tested a novel hybrid, multi-scale micro-electrocorticography (micro-ECoG) array with a unique embedded configuration. This array was compared to a commercially available microelectrode array (Neuronexus) for recording neural activity in rodent sensory cortex elicited by somatosensory evoked potentials and pilocarpine-induced seizures.Main results.Evoked potentials and spatial maps recorded by the multi-scale array ('micros', 'mesos', and 'macros' refering to the relative electrode sizes, 40 micron, 1 mm, and 4 mm respectively) were comparable to the Neuronexus array. The SSEPs recorded with the micros had higher peak amplitudes and greater signal power than those recorded by the larger mesos and macro. Seizure onset events and high-frequency oscillations (â¼450 Hz) were detected on the multi-scale, similar to the commercially available array. The micros had greater SNR than the mesos and macro over the 5-1000 Hz frequency range during seizure monitoring. During cortical stimulation experimentation, the mesos successfully elicited motor effects.Significance.Previous studies have compared macro- and microelectrodes for localizing seizure activity in adjacent regions. The multi-scale design validated here is the first to simultaneously measure macro- and microelectrode signals from the same overlapping cortical area. This enables direct comparison of microelectrode recordings to the macroelectrode recordings used in standard neurosurgical practice. Previous studies have also shown that cortical regions generating high-frequency oscillations are at an increased risk for becoming epileptogenic zones. More accurate mapping of these micro seizures may improve surgical outcomes for epilepsy patients.
Subject(s)
Electrocorticography , Evoked Potentials, Somatosensory , Microelectrodes , Seizures , Electrocorticography/instrumentation , Electrocorticography/methods , Animals , Seizures/diagnosis , Rats , Male , Electrodes, Implanted , Somatosensory Cortex , Equipment Design , Rats, Sprague-Dawley , Brain Mapping/methods , Pilocarpine , EpilepsyABSTRACT
Ultrasound (US) is known to non-invasively stimulate and modulate brain function; however, the mechanism of action is poorly understood. This study tested US stimulation of rat motor cortex (100 W/cm2, 200 kHz) in combination with epidural cortical stimulation. US directly evoked hindlimb movement. This response occurred even with short US bursts (3 ms) and had short latency (10 ms) and long refractory (3 s) periods. Unexpectedly, the epidural cortical stimulation hindlimb response was not altered during the 3-s refractory period of the US hindlimb response. This finding suggests that the US refractory period is not a general suppression of motor cortex, but rather the recovery time of a US-specific mechanism.
Subject(s)
Electric Stimulation/methods , Motor Cortex/physiology , Ultrasonography/methods , Animals , Epidural Space , Male , Models, Animal , Rats , Rats, Sprague-Dawley , Ultrasonic WavesABSTRACT
A single diode with a wireless power source and electrodes can act as an implantable stimulator or sensor. We have built such devices using RF and ultrasound power coupling. These simple devices could drastically reduce the size, weight, and cost of implants for applications where efficiency is not critical. However, a shortcoming has been a lack of control: any movement of the external power source would change the power coupling, thereby changing the stimulation current or modulating the sensor response. To correct for changes in power and signal coupling, we propose to use harmonic signals from the device. The diode acts as a frequency multiplier, and the harmonics it emits contain information about the drive level and bias. A simplified model suggests that estimation of power, electrode bias, and electrode resistance is possible from information contained in radiated harmonics even in the presence of significant noise. We also built a simple RF-powered stimulator with an onboard voltage limiter.
Subject(s)
Implantable Neurostimulators , Wireless Technology/instrumentation , Computer Simulation , Electric Power Supplies , Electricity , Electrodes , Humans , Models, Theoretical , Movement , Radio WavesABSTRACT
We have previously shown a small simple ultrasound-powered nerve stimulator. The piezoelectric implant receives power from an external driving ultrasound transducer. Focusing the ultrasound beam improves power transfer efficiency, but the implant location must be known to aim the focus. We show that currents driven by the stimulator might be detectable on the skin. By scanning the ultrasound focus and measuring the electrical response, we form an image of the implant location. This could give a feedback signal for aiming the beam, and allow multichannel addressing of several stimulators with no added circuitry in the implant.
Subject(s)
Electric Stimulation Therapy/instrumentation , Electric Stimulation Therapy/methods , Electrodes, Implanted , Models, Biological , Sound , Animals , Humans , Peripheral NervesABSTRACT
An unexpectedly simple implantable device that can achieve wireless neurostimulation consists of a short 1 cm long dipole platinum wire antenna, a Schottky diode, and a pulsed microwave transmitter. Fabricated into a 1 cm long by polyimide tubing, the implant can have a sub-millimeter diameter form factor suited to introduction into tissue by injection. Experiments that chronically implant the device next to a rat sciatic nerve show that a 915 MHz microwave transmitter emitting an average power of 0.5 watts has an ability to stimulate motor events when spaced up to 7 cm from the body surface. Tissue models consisting of saline filled tanks show the possibility of delivering milliampere pulsed current to neurosimulators though 5 centimeters or more of tissue. Such a neurostimulation system driven by microwave energy is limited in functional tissue depth by microwave SAR exposure. This report discusses some of the advantages and limitations of such a neurostimulation approach.
Subject(s)
Action Potentials/physiology , Electric Power Supplies , Electric Stimulation/instrumentation , Neurons/physiology , Prostheses and Implants , Semiconductors , Wireless Technology/instrumentation , Animals , Equipment Design , Equipment Failure Analysis , Humans , Injections , MicrowavesABSTRACT
A miniature piezoelectric receiver coupled to a diode is evaluated as a simple device for wireless transmission of bioelectric events to the body surface. The device converts the energy of a surface-applied ultrasound beam to a high frequency carrier current in solution. Bioelectrical currents near the implant modulate the carrier amplitude, and this signal is remotely detected and demodulated to recover the biopotential waveform. This technique achieves millivolt sensitivity in saline tank tests, and further attention to system design is expected to improve sensitivity.
