Transcranial Magnetic Stimulation (TMS)

Division Chief: Felipe Salinas, Ph.D.

 

Transcranial Magnetic Stimulation Laboratory

The focus of the Transcranial Magnetic Stimulation (TMS) laboratory is to enhance the precision and ease with which TMS can be used for the diagnosis and treatment of neurological and psychiatric disorders and for neuroscience research. TMS is the newest and least invasive form of electrical brain stimulation. It is being developed for clinical application in pre-surgical mapping and in treatment of depression. It is also being used in neuroscientific applications to examine neural connectivity, reversible-lesion cognitive mapping, and chronometry of brain processing. Approximately 4/5 of the studies are in normal subjects; 1/5 of the studies are in patients.

Subject Testing Room: Subjects are tested in a room with a state-of-the-art PC running Neuroscan (for electrophysiology) and E-Prime (for integrated control of TMS stimulus, psychological stimuli, and subjects’ responses), an examination table, color monitor for visual presentation, and headphones.

Cadwell TMS: The RII’s primary human transcranial magnetic stimulation system is a Cadwell High Speed Magnetic Stimulator (HSMS) (Kennewick, Washington). This stimulator uses a B-shaped coil. The peak energy transfer to the coil is 225 joules. The stimulator produces a symmetric bi-phasic pulse with a total duration of about 250 µs. It is capable of delivering pulses at a rapid rate of up to 25 Hz with no reduction in intensity. The maximum rate is 60 Hz at 40% of maximum intensity. We have 2 systems.

Magstim TMS: The RII also has another transcranial magnetic stimulation system, Magstim BiStim Module (The Magstim Co. Ltd. Wales, UK). This stimulator uses a B-shaped coil. The stimulator produces a symmetric mono-phasic pulse with a total duration of about 500 µs. It is capable of delivering pulses at a slow rate of up to 0.25 Hz at maximum intensity. Two small animal coils (2 and 4 loop) are available for use with this system.

NeuroMate Robotic System: The NeuroMate Robotic System includes a five-axis robot arm; robot base and head support frame; and (ActMate) workstation. It was specifically conceived and designed for use by and with humans. It is the only robot approved by the FDA for use in neurosurgical application and the only device of its kind adapted to precise, safe, programmable positioning, with on-line co-referenced spatial coordinate systems. From 1989-1995, over 2500 neurosurgical procedures have been performed with NeuroMate. The NeuroMate Robotic System includes a five-axis robot arm; robot base and head support frame; and (ActMate) workstation. The tool holder contains sensors suitable for monitoring rotational movement of the tool in the holder. The NeuroMate has automatic self-blocking joints, sensor redundancy, and an embedded controller, which are key to its accuracy and safety. All joints are powered by worm gears, making them very stable (for tool holding) and absolutely rigid during power surges and loss. Once positioned, the NeuroMate can be de-powered with no change of position; it does not return to a home position. It is an automatic and extremely accurate positioning device. Its absolute accuracy (positioning 0.75 mm; orientation 0.125°) and repeatability (positioning 0.15 mm; orientation 0.02°) are well suited for accurate positioning of TMS coils at the scalp. Positions are achieved within 45 seconds, directly after trajectory validation on the image planner. The NeuroMate has no geometric limitations due to mechanics. The patient’s head always remains accessible. It has low EM emission, easy cleaning, and ergonomic design appropriate to experimental environment. Its inherent safety features and built-in controls will be efficiently integrated into a 2nd generation TMS- AHRM system in the future.

Microscribe Digitizer: The MicroScribe 3DLX, from Immersion Corp. (San Jose, CA) is a precision mechanical arm used to acquire 3D coordinates (see figure). The arm has five axes with precise encoders, which combine to track the position and orientation of the stylus tip. This particular version of the arm has a spherical workspace of 66" (1.67 meters) and an accuracy of 0.012" (0.30 mm). It supports RS232 serial interface to host computer, and has an internal sampling rate of 1000 per second.

Electromyography (EMG): The TMS lab has a Neuroscan SynAmps 32 channel EEG/ERP system running Scan 4.3 acquisition and analysis software that is used to record EMG. In addition there is a custom 8-channel double differential surface EMG (sEMG) system (Motion Lab Systems, Baton Rouge, LA). The TMS lab also has SML-10 strain gauges and a 9840 intelligent indicator (Interface, www.interfaceforce.com) to provide constant feedback of the muscle forces.

E-Field Measurement: Currently we measure the electric field using both a custom-made dipole probe and a custom-made coil probe. The output from these probes is measured using a Tektronix TDS 320 100 MHz, 2-channel digital oscilloscope. We have calculated and verified comprehensive 3-D E-Field maps for all TMS coils.

 

Behavioral Apparatus: RII investigators also conduct psychological experiments to develop the behavioral paradigms that serve as the basis for PET and TMS experiments, as well as for fMRI and ERP studies. In these experiments, a computer presents visual or auditory stimuli and collects either verbal, button-press, or joystick responses from a subject, which then can be analyzed for accuracy, reaction times, or other behavioral parameters. These computer experiments are conducted using either E-Prime (Psychology Software Tools, Inc.) on PC platform, SuperLab (Cedrus, Inc.) on an Apple or PC platform. Further the laboratory has audio and video recording capabilities during motor and speech studies.

 

TMS Funded Grants:

1. “Mechanisms of Action of TMS-Induced Performance Enhancement.” VA Merit award. PI: Peter T. Fox.

The overall goal of this project is 1) to determine the mechanisms of action of short-term (single stimulation session) TMS-induced performance enhancement. 2) To determine the mechanisms of action of long-term (multiple stimulation sessions) TMS-induced performance enhancement.

2. “Image-Guided Robotically-Positioned TMS System.” 1 R41 MH074278-01. PI: Jack L. Lancaster.

The overall goals for Phase I are: 1) incorporate current irTMS treatment planning and delivery control software, 2) add hardware specific for the new robot, and 3) test the new irTMS system by comparison with the current irTMS system.

3. “Imaging and Modeling Therapeutic Mechanisms of Action.” R21 NS43738. PI: Peter T. Fox.

The major goals of this project are to develop system-level modeling strategies for neuroimaging and to apply these novel strategies to mechanisms of action of motor learning.

4. “Imaging Mechanisms of Action in Motor Learning.” BCS- 0225711. PI: Jinhu Xiong

The major goals of this project are to develop system-level modeling strategies for neuroimaging and to apply these novel strategies to mechanisms of action of motor learning.

5. “Robotic Image-Guided Transcranial Magnetic Stimulation.” R01 MH60246-03. PI: Peter T. Fox.

The major goal of this project is to enhance the precision and ease with which transcranial magnetic stimulation (TMS) can be used for the diagnosis and treatment of neurological and psychiatric disorders and for neuroscience research.