ALTERATIONS OF AFFECTIVE AND AUTONOMIC RESPONSES
WITH TRANSCEREBRAL COMPLEX MAGNETIC FIELDS:
DAILY VERSUS WEEKLY SCHEDULE

E. W. Tsang,  M. A. Persinger,  S. A. Koren
Neuroscience Research Group, Laurentian University,
Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 2C6

Abstract: The present studies investigated the autonomic & affective changes of normal subjects following repeated stimulation with weak but complex magnetic fields under two treatment schedules. In experiment one, 24 university students were exposed to one of two configurations of weak (1 microTesla) magnetic fields or to a sham field for 20 min per session for three sessions. The treatments were delivered for either 3 consecutive days or once per week for 3 weeks. The fields were applied to the frontotemporal region bilaterally. Psychometric index—Profile of Mood State was administrated before and after each treatment session. Autonomic measures including skin conductance, photoplethysmograph, and heart rate were completed before, during, and after the treatments. The results from experiment one indicated that the weekly treatment schedule was more effective than the daily schedule for altering subjects’ autonomic responses as well as improving emotional responses. Experiment two involved treating a total of 32 normal university students with one of seven configurations of weak magnetic fields or a sham field. The treatment procedure in experiment two was identical to that in experiment one except that all subjects were treated for once per week for 3 sessions. The results for experiment two indicated that weak magnetic fields whose patterns resembled patterns generated by neurons within the amygdoid nucleus were effective in reducing subjects’ level of depression.

Introduction

Baker-Price and Persinger (1996) reported that stimulating the temporal areas bilaterally with weak (1 microTesla) complex magnetic fields whose pattern resembled burst firings of the amygdoid nucleus could reduce chronic clinical depression for brain-injured patients. The stimulation was delivered once per week for 30 min for a total of 5 weeks. The results after 5 weeks of treatment indicated that all patients showed a reduction in their scores for depression (h²=67%) as measured by the Beck Depression Inventory. The most conspicuous reduction in depression score was observed after the third week of treatment i.e. after 3 sessions of treatment.

The present studies were designed to test the generalizability of the Baker-Price and Persinger (1996) experiment with normal healthy university students. In experiment 1, we applied a 20 min per session treatment to normal subjects in order to compare the effects of two different patterns of weak magnetic fields and two schedules of delivery: once per day versus once per week. Following experiment 1, experiment 2 was designed to deliver a 20 min stimulation per session in a once per week schedule for 3 week to compare 8 different patterns of weak magnetic stimulation. We would like to know whether different patterns could produce different results in affective responses as well as physiological measures.

Method

Subject

Subjects in experiment 1 were 12 male and 12 female university students aged 20 to 25 years. They were randomly assigned to one of three treatment groups: 20 min burst firing pulse, 10 min of burst firing followed by 10 min of theta pulse, or 20 min of sham treatment. Half of the individuals were treated once daily for 3 consecutive days; the other half were treated once per week for 3 weeks. 

Participants for experiment 2, consisted of 32 male and female students, were randomly assigned to one of eight groups and were treated for 20 min per session for 3 sessions approximately once per week. The 8 treatment conditions were— 20 min burst firing; 10 min burst firing followed by 10 min of theta pulse; 20 min theta pulse with interstimulus interval (ISI) of 4000 msec; 20 min theta pulse with ISI=20 msec; 20 min of complex sequence pattern; 20 min of sham treatment; 20 min of random pattern with ISI=1 msec, and 20 min of random pattern with ISI=3000 msec.

Procedure           

Each subject was individually tested for 3 sessions in both experiments. During the experiment, the subject sat on a comfortable chair. Autonomic responses including the galvanic skin response, photoplephysmograph, and heart-rate were recorded before, during, and after the treatment. The Profile of Mood State was administered before the treatment. After filling out the psychometric test, a pair of modified headphones embedded with 4 pairs of solenoids was placed on the subject’s temporal areas bilaterally. The subject was blindfolded and earmuffed to reduce sensory inputs. A weak (1mT) patterned magnetic fields that passed through the temporal areas was delivered through the 4 pairs of solenoids for 20 min. The subjects who were assigned to the sham group was exposed to sham field for 20 min. Approximately 5 min after the treatment, the subject was re-administered the Profile of Mood States.

Results

To minimize individual differences, relative changes were calculated for the autonomic measures and scores for the psychometric scale by dividing the post-treatment scores with the pre-treatment scores. The results from experiment 1 indicated that the group who received the burst firing pulse displayed a lower heart-rate than those in other groups [F(2,21)=6.67, p<0.01, h²=.28] during the first treatment session (see Figure 1).

Figure 1. Relative changes in heart-rate during the first 20 min exposure to magnetic fields.

The group who received weekly burst firing showed lower depression scores compared to other groups after 3 sessions of treatment [F(5,23)=2.70, p=.05, h² =.44]. This indicated that weekly treatment was more effective than daily treatment (see Figure 2).

Figure 2. Relative changes in depression scores after 3 daily or 3 weekly treatments.

The results from experiment 2 showed that burst firing was the most effective pattern to produce attenuation of depression after 3 weeks of treatments [F(7,24)=2.05, p=.08, h² =.50]. The group who received theta pulse ISI=4000 msec had lower fatigue [F(7,24)=2.56, p=.04, h2 =.53] and confusion scores [F(7,24)=1.08, p<.13, h²=.34] than the sham and the theta pulse ISI=20 msec groups after 3 weeks of treatment.

Discussion

The present study was the first to present evidence that complex weak (1mTesla) magnetic fields produced changes in human physiological responses. It also showed that the amygdoid burst firing pattern magnetic fields reduced depression on normal subjects as well as brain-injured patients as shown in previous clinical studies. Another discovery was that the theta pulse pattern produced contradictory effects on subjects after 3 weeks of treatment when given different interstimulus intervals. The results were consistent with previous findings in human and animal studies regarding the influence of (1mT) theta pulse magnetic fields on verbal and spatial learning (Persinger, Richards, & Koren, 1994; McKay, Persinger, & Koren, 2000). In summary, weak patterned magnetic fields tended to produce positive effects on subjects with interstimulus interval around 4000 msec; however, more negative effects were produced when the interstimulus interval was shortened i.e. 20 msec and 1 msec. It was thereby suggested that weak patterned magnetic fields served as enhancers of intrinsic neural activities. Specific temporal parameters determined the different effects.

References

[1] L. A. Baker-Price & M. A. Persinger. “Weak, but complex pulsed magnetic fields may reduce depression following traumatic brain injury,” Percept Mot Skills, 83(2),491-8, 1996.

[2] M. A. Persinger, P. M. Richards, S. A. Koren. “Differential ratings of pleasantness following right and left hemispheric application of low energy magnetic fields that stimulate long-term potentiation,” Int J Neurosci, 79(3-4), 191-7, 1994.

[3] B. E. McKay, M. A. Persinger, S. A. Koren. “Exposure to a theta-burst patterned magnetic field impairs memory acquisition and consolidation for contextual but not discrete conditioned fear in rats,” Neurosci Lett, 292(2), 99-102, 2000.