Study type: Medical/biological study (experimental study)

Exposure to a theta-burst patterned magnetic field impairs memory acquisition and consolidation for contextual but not discrete conditioned fear in rats. med./bio.

Published in: Neurosci Lett 2000; 292 (2): 99-102

Aim of study (acc. to editor)

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.

Background/further details

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.

Endpoint

Exposure

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:
  • unspecified
Modulation type: pulsed
Exposure duration: 30 min

Exposure 1

Main characteristics
Frequency 7 Hz
Type
Waveform
Exposure duration 30 min
Exposure setup
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.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 400 nT maximum unspecified - -

Exposure 2

Main characteristics
Frequency 20 Hz
Type
Waveform
Exposure duration 30 min
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 900 nT maximum unspecified - -

Exposure 3

Main characteristics
Frequency 100 Hz
Type
Waveform
Exposure duration 30 min
Additional info magnetic field with theta burst stimulation pattern was used.
Modulation
Modulation type pulsed
Additional info

The pattern consisted of 5 pulse bursts of 100 Hz separated by 140 ms.

Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 500 nT maximum unspecified - -

Exposure 4

Main characteristics
Frequency
  • unspecified
Type
Waveform
Exposure duration 30 min
Modulation
Modulation type pulsed
Additional info

burst firing pattern (not further specified)

Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 900 nT mean unspecified - -

Reference articles

  • Richards PM et al. (1993): Modification of activation and evaluation properties of narratives by weak complex magnetic field patterns that simulate limbic burst firing.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by

Replication studies

Related articles