Magnetic field treatment techniques
The invention involves enhancing brain function by stimulating the brain using magnetic fields. Applications of the new methods include improving the condition of individuals with cognitive disorders, such as depression, and studying the effects of neural stimulation using induced electric fields. These techniques can avoid deleterious effects of psychotropic pharmaceutical treatments, and provide a relatively safe, comfortable, inexpensive means of direct cranial stimulation.
1. A system comprising:
a magnetic coil configured to produce a magnetic field in response to an electrical signal; and
a waveform generator comprising a computer programmed to produce the electrical signal such that the magnetic field comprises a time-varying magnetic field with a maximum strength of less than 50 G,
wherein the magnetic field induces an electric field in air comprising a series of electric field pulses, and
wherein the electric field pulses are monophasic and consecutive electric field pulses are separated by periods of substantially no electric field, wherein the periods have non-zero durations.
2. The system of claim 1 , wherein the maximum strength of the magnetic field is less than 10 G.
3. The system of claim 1 , wherein the electric field pulses have amplitude less than 10 V/m.
4. The system of claim 3 , wherein the duration of each electric field pulse is less than or equal to 10 milliseconds.
5. The system of claim 1 , wherein the duration of each electric field pulse is less than or equal to 1 millisecond.
6. The system of claim 1 , wherein a spatial gradient of the magnetic field is substantially uniform.
7. The system of claim 6 , wherein the magnetic coil is configured to generate the magnetic field over a region of interest.
8. The system of claim 1 , wherein the magnetic coil is configured to receive at least a portion of a subject's head within the coil.
9. The system of claim 1 , wherein at least one of the periods have a duration substantially equal to 768 microseconds.
10. A waveform generator comprising a computer programmed to produce an electrical signal for delivery to a magnetic coil such that the magnetic coil produces a time-varying sequence of magnetic field pulses in response to the electrical signal,
wherein each of the magnetic field pulses is unidirectional and has a substantially uniform spatial gradient, and wherein the magnetic field pulses induce electric field pulses such that the electric field pulses are monophasic and consecutive electric field pulses are separated by periods of substantially no electric field, wherein the periods have non-zero durations.
11. The waveform generator of claim 10 , wherein the maximum strength of the magnetic field pulses is less than 50 G.
12. The waveform generator of claim 10 , wherein the time varying sequence of magnetic field pulses comprises pulses each having a duration less than about 10 milliseconds and being trapezoidal shaped with a plateau between two magnetic field ramps.
13. The waveform generator of claim 10 , wherein the maximum strength of the magnetic field pulses is less than 500 G.
14. A waveform generator comprising a computer programmed to produce an electrical signal for delivery to a magnetic coil, the magnetic coil producing a magnetic field in response to the electrical signal, the magnetic field comprising a time-varying magnetic field, wherein the magnetic field induces an electric field in air comprising a series of electric field pulses, wherein the series of electric field pulses has a frequency of at least about 100 Hz, and wherein each electric field pulse has a single polarity and consecutive electric field pulses are separated by periods of substantially no electric field, wherein the periods have non-zero durations.
15. The waveform generator of claim 14 , wherein the maximum strength of the magnetic field is less than 50 G.
16. The waveform generator of claim 14 , wherein the electric field pulses have an amplitude less than 10 V/m.
17. The waveform generator of claim 14 , wherein the electric field pulses have an amplitude less than 5 V/m.
18. The waveform generator of claim 14 , wherein the time varying magnetic field comprises a sequence of magnetic field pulses each having a duration less than 10 milliseconds and being trapezoidal shaped with a plateau between two magnetic field ramps.
19. The waveform generator of claim 18 , wherein each electric field pulse is generated during field ramps of two succeeding magnetic field pulses.
20. The waveform generator of claim 18 , wherein the periods of substantially no electric field correspond to the plateaus of the trapezoidal shaped magnetic field pulses.
21. The waveform generator of claim 14 , wherein the frequency of the series of the electric field pulses is 1 kHz.
22. The waveform generator of claim 21 , wherein the series of electric field pulses comprises multiple pulse trains, wherein each pulse train comprises 512 pulses and lasts a half second and wherein successive pulse trains are separated by one and a half seconds.
23. The waveform generator of claim 14 , wherein the maximum strength of the magnetic field is less than 500 G.
24. A waveform generator comprising a computer programmed to produce an electrical signal such that a magnetic field is produced by a magnetic coil in response to the electrical signal, the magnetic field comprising a time-varying magnetic field,
wherein the magnetic field induces an electric field in air comprising a series of electric field pulses, wherein the electric field is substantially unidirectional over at least a region of the brain, and wherein each electric field pulse has a single polarity and consecutive electric field pulses are separated by periods of substantially no electric field, wherein the periods have non-zero durations.
25. The waveform generator of claim 24 , wherein the maximum strength of the magnetic field is less than 50 G.
26. The waveform generator of claim 25 , wherein the electric field pulses have an amplitude less than 10 V/m.
27. The waveform generator of claim 24 , wherein the electric field pulses have an amplitude less than 5 V/m.
28. The waveform generator of claim 27 , wherein the duration of each electric field pulse is less than or equal to 10 milliseconds.
29. The waveform generator of claim 24 , wherein the duration of each electric field pulse is less than or equal to 1 millisecond.
30. The waveform generator of claim 24 , wherein the frequency of the series of the electric field pulses is at least 100 Hz.
31. The waveform generator of claim 24 , wherein the maximum strength of the magnetic field is less than 500 G.