To investigate whether magneto-sensory evoked potentials triggered by magnetic fields could be mediated by a biophysical mechanism actually involving only the electric field component.
Previous studies (Carrubba et al., 2008; Carrubba et al., 2007a; Carrubba et al., 2007b) have shown that weak low frequency magnetic fields trigger magneto-sensory evoked potentials. Because the magnetic fields and their induced electric fields were both present in the brain the distinct influence of the components (magnetic/electric) on brain activity is unclear.
23 subjects (six males) were exposed to electric fields whose strength was capable of producing brain electric fields comparable to those of magnetic fields from the previous studies (see above). To test the sensitivity, the strength of the electric field was systematically reduced and was always below the threshold for awareness. Sham exposure (negative control) was performed randomly before or after exposure.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
60 Hz
Modulation type:
pulsed
Exposure duration:
80 pulses
|
|
| Frequency | 60 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 80 pulses |
| Exposure source |
|
|---|---|
| Setup | plates inside an electrically grounded room, test person's head between the plates; field perpendicular to the sagittal plane |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| electric field strength | 1 V/m | - | calculated | - | - |
| electric field strength | 1,000 V/m | peak value | calculated | - | - |
| electric field strength | 1 mV/m | - | calculated | - | induced in the brain |
Evoked potentials were observed in all but one subject in response to electric fields. The evoked potentials had the same latency, duration and distribution of magnitudes as the potentials triggered by magnetic fields in earlier studies (see above). Evoked potentials were not detected based on EEG analysis using time averaging, but only by means of recurrence analysis. No sensitivity threshold could be determined.
It was concluded that the electric field was a sufficient biophysical determinant of the evoked potentials in this study and previous studies. The transduction of an electric field could be explained by biophysical coupling between fields and tissue by processes involving forces on ion channel gates.
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