Safety

In progress.


Safety comprises three parts:
1) the device should not be allowed to enter physically unsafe limits,
2) if some component within the device fails, the device should fail in a direction that avoids damage or injury, and
3) the device should not be allowed to enter neurophysiologically unsafe regimes, for any given subject.

The first concern can be accomplished in a number of ways: hardware current limiting in the coil, having a physical fuse or shunt to prevent current from exceeding a limit, or using a magnetometer to physically feedback the rate of magnetic field change, and shutdown device operation if the device exceeds a certain rate. Care must also be taken that the capacitor not discharge when the coil is not connected. Standard preventative care on the power supply side should be taken.

The second requires that all designs be self-correcting, and/or fault-tolerant. For example, control circuit failure should not leave the capacitors charged indefinitely; accordingly, a shunt resistor should exist to short out the cap (much like for the magnetron of a microwave). The capacitors should not charge, nor discharge, without a proper command signal — the default state should be to retain each component separately in an open circuit with respect to the external world. Overheating of the coil, or excessive mechanical deformation of the coil, must be sensed and lead to shutdown of the device, or to activation of cooling circuits or other means of remedying the deficit in device operation.

The third concern requires
a) human attentiveness to make sure that subjects with certain conditions not be stimulated,
b) software and hardware limits to prevent stimultation with inappropriate parameters (e.g., too-high amplitudes or too-high rates), and
c) monitoring of muscle and brain activity to actively feedback and modulate stimulator function, to prevent excessive stimulation.

a. Subjects. No systematic consensus has been arrived at for children or adolescents; accordingly, subjects under the age of 18 should not be stimulated, nor operate the machine. No subject with a history of epilepsy or any neuropsychiatric condition, nor taking any medications that alter neural excitability, should be stimulated, except under the supervision of a clinical neurophysiologist who has approved the procedure. Note that it is always possible that a subject undergoing TMS has a latent neural excitability condition, which could be revealed by rapid-rate stimulation. It is recommended that all experimenters read the International Federation on Clinical Neurophysiology's "Information Brochure on Repetitive Transcranial Magnetic Stimulation (rTMS)" for considerations on this issue, which recommends when a neurologist should be consulted (e.g., if you have a family history of epilepsy, have a history of seizures, or are on medication).

b. Stimulation parameters. TMS of sufficiently high amplitude, or high stimulation rate, can cause a seizure, even in normal humans. The NINDS held a conference from June 5-7, 1996 in which safety recommendations for TMS operation in neurologically normal, unmedicated humans were arrived at, shown in the figure below. Following these recommendations, in a neurologically normal human who is not taking medications that increase neural excitability, reduces the risk to an extremely low level. In the rare event that a seizure does occur in a normal human while following the guidelines presented below, no lasting damage has ever been documented. In fact, the greatest side effect of a TMS-induced seizure is that the subject may worry about having more seizures; this of course is not to be taken lightly. In our project, we should enforce these constraints at the software level.

Wassermann, E. M. (1998) Electroencephalography and Clinical Electrophysiology, 108:1-16

c. Feedback. Monitoring of the hand muscles using an electromyography (EMG) device is important, both for accurately tuning the motor threshold of the stimulator under normal operation, and to monitor when stimulation of non-motor areas (e.g., frontal, parietal, or occipital cortex) leads to spread of excitation to the thumb area (abductor pollicis brevis). Such spread should lead to termination of stimulator operation. In addition, we will design our open-source brain stimulator to monitor brain activity via EEG or IR imaging, to provide means for feedback, modulation, and even shutdown of the stimulator device.


Under exploration.


None yet.


None yet.


None yet.


None yet.

---

The text and graphics of this site are released under a Creative Commons license unless otherwise stated. You are free to copy, distribute, utilize, or display the works, or even to make commercial use of the works found herein, as long as you give attribution for your use of that information, in the context of whatever derivative works or products you create or devise, to the OpenStim Project, and release your works under an identical license. For administrative queries please email openstimadmin@transcenmentalism.org.