To study the exposure to either one of two symmetrical magnetic fields or to one of two complex magnetic fields on memory acquisition and consolidation of contextual fear conditioning in rats.
Animals were placed in a conditioning chamber and received four footshocks (with/without prior presentation of a discrete auditory stimulus/tone). Subsequently rats were removed from the chamber and placed in their home cages. Freezing to contextual cues was assessed 24 hours later when rats were returned to the conditioning chamber. Rats were exposed either before or immediately after the conditioning.
The two complex magnetic fields were a theta-burst patterned (similar to prominent hippocampal electrophysiological pattern; to mimic the firing parameters of hippocampal pyramidal cells during learning) and a amygdaloid complex burst-firing (modeled after recordings of amygdaloid activity in epileptic patients) magnetic field.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
7 Hz
Exposure duration:
30 min
|
|
|
Exposure 2:
20 Hz
Exposure duration:
30 min
|
|
|
Exposure 3:
100 Hz
Modulation type:
pulsed
Exposure duration:
30 min
|
|
Exposure 4:
Modulation type:
pulsed
Exposure duration:
30 min
|
|
| Frequency | 7 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 30 min |
| Exposure source | |
|---|---|
| Setup | 30 cm x 30 cm x 30 cm plexiglas box with 6 solenoids affixed perpendicular to the center of each external face of the cube |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 400 nT | maximum | unspecified | - | - |
| Frequency | 20 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 30 min |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 900 nT | maximum | unspecified | - | - |
| Frequency | 100 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 30 min |
| Additional info | magnetic field with theta burst stimulation pattern was used. |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 500 nT | maximum | unspecified | - | - |
| Frequency |
|
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 30 min |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 900 nT | mean | unspecified | - | - |
Only the rats exposed after the conditioning to the theta-burst (hippocampal) magnetic fields displayed evidence of forgetting, as inferred by their marked attenuation of freezing behavior 24 hours later. Behavioral responses to the discrete conditioned stimulus (2.) were not influenced. All other treatment conditions did not differ significantly from each other. Because the two sinusoidal magnetic field treatments did not influence contextual extinction testing (1.), they were excluded from additional experiments.
The results are consistent with the involvement of the hippocampus in learned fear to contextual stimuli but not to discrete auditory stimuli.
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