The anatomic location of magnetic field sensing in rabbits should be determined by partial body exposure to a 60 Hz magnetic field.
The EEG of 10 rabbits was recorded during several exposure trials. Each trial lastet 7 seconds, with exposure during the first 2 seconds (exposure condition) and no exposure during the other 5 seconds. The last 2 seconds (second 6 and 7) of each trial were definded as the control condition and seconds 4 and 5 were defined as the sham exposure condition (used to verify the control condition).
The area of exposure was scaled down decreasingly to identify the location of magnetic field sensing. First, a whole body exposure was conducted, then the front and back body half were exposed separately. Afterwards, exposure was focused on the head and finally on the eye of each animal. For each exposure condition, n=50 trials were recorded.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
60 Hz
Exposure duration:
intermittent (2 s field on, 5 s field off) 50 times
|
|
|
Exposure 2:
60 Hz
Exposure duration:
intermittent (2 s field on, 5 s field off) 50 times
body halfs exposure
|
|
|
Exposure 3:
60 Hz
Exposure duration:
intermittent (2 s field on, 5 s field off) 50 times
head exposure
|
|
|
Exposure 4:
60 Hz
Exposure duration:
intermittent (2 s field on, 5 s field off) 50 times
|
|
the average geomagnetic field was 30.5 µT, 22° below the horizontal; the geomagnetic component along the direction of 60 Hz was 23.9 µT
| Frequency | 60 Hz |
|---|---|
| Type | |
| Exposure duration | intermittent (2 s field on, 5 s field off) 50 times |
| Additional info | whole body exposure |
| Exposure source |
|
|---|---|
| Chamber | rabbits were restrained in an acrylic box, which was positioned in a light tight wooden box which was centered in the exposure unit such that its axis and the rabbit`s rostral-caudal axis were parallel |
| Setup | multiple-turn coils of 12-gauge magnet wire; coaxial configuration of four square coils, each 66 cm on a side; field was 5% homogeneous in exposure area; the outer coils (85 turns each) were ± 33.4 cm from the unit's centerline; the inner coils (35 turns each) ± 8.5 cm |
| Sham exposure | A sham exposure was conducted. |
| Additional info | control coils produced the same heat but no magnetic field |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 250 µT | spatial average | measured | - | - |
| Frequency | 60 Hz |
|---|---|
| Type | |
| Exposure duration | intermittent (2 s field on, 5 s field off) 50 times |
| Additional info | body halfs exposure |
| Exposure source |
|
|---|---|
| Chamber | see E1 |
| Setup | like E1 but the magnitudes and phases of the coil currents were chosen such that one half of the body was exposed stronger |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 250 µT | peak value | measured | - | in exposed body half |
| magnetic flux density | 220 µT | mean | measured | - | ± 60 µT; in exposed body half |
| magnetic flux density | 50 µT | mean | measured | - | ± 30 µT; in non-exposed body half |
| Frequency | 60 Hz |
|---|---|
| Type | |
| Exposure duration | intermittent (2 s field on, 5 s field off) 50 times |
| Additional info | head exposure |
| Exposure source |
|
|---|---|
| Distance between exposed object and exposure source | 4 cm |
| Chamber | see E1 |
| Setup | pair of 14-turn coils, each 5 cm in diameter and located 9 cm apart one on each side of the head with a distance of approx. 4 cm to the center of the brain |
| Sham exposure | A sham exposure was conducted. |
| Additional info | sham exposure served as temperature control |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 250 µT | spatial average | measured | - | - |
| Frequency | 60 Hz |
|---|---|
| Type | |
| Exposure duration | intermittent (2 s field on, 5 s field off) 50 times |
| Additional info | eye exposure |
| Exposure source |
|
|---|---|
| Distance between exposed object and exposure source | 0.5 cm |
| Chamber | see E1 |
| Setup | 24-turn coil, 2 cm in diameter, with a distance of approximately 0.5 cm to the cornea |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 280 µT | spatial average | measured | - | ± 50 µT; average over the retina |
Whole body exposure led to significant changes in the EEG compared to the control condition. Exposure of the front half of the body led to a comparative result, whereas no changes could be observed when the back half was exposed. Further exposure of the head resulted in significant changes in the EEG in comparison the control condition, while an exposure of the eye did not show significant EEG changes.
There were no significant differences between control and sham exposure conditions.
The authors conclude that sensing of the 60 Hz magnetic field occurs in in the head of rabbits, probably in the brain.
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