Erik Nilsen | PubMed Health

PubMed2004

Effect of low-frequency magnetic fields on brain electrical activity in human subjects.

OBJECTIVE: To measure the response rate of normal human subjects to a low-strength, low-frequency magnetic field (MF), using nonlinear quantitative analysis of the electroencephalogram (EEG). METHODS: Eight subjects were exposed to a series of trials, each consisting of the application of the MF (1 G, 60 Hz) for 2 s followed by a field-free period of 5 s, and the EEG was analyzed statistically using phase-space methods to assess whether the subject detected the MF. RESULTS: Each subject exhibited statistically significant changes in the EEG during presentation of the MF, as evidenced by increases in percent determinism and percent recurrence, two different measures of deterministic structure in the recorded signal, thereby indicating that the MF had been detected. CONCLUSIONS: The 100% response rate manifested by the study group suggested that the ability to detect low-strength, low-frequency MFs is a common property of the human nervous system.

Adult↗

PubMed2003

Consistent magnetic-field induced dynamical changes in rabbit brain activity detected by recurrence quantification analysis.

The reports dealing with the effects of electromagnetic fields (EMFs) on brain electrical activity have been inconsistent. We suspected that the use of linear methods and models accounted for some of the variability, and we explored the issue by using a novel approach to study the effects of EMFs on the electroencephalogram (EEG) from rabbits. The EEG was embedded in phase space and local recurrence plots were calculated and quantified to permit comparisons between exposed and control epochs from individual animals. Statistically significant alterations in brain activity were observed in each animal (n=10) when it was exposed to 2.5 G, 60 Hz, as assessed using each of two recurrence-plot quantifiers. Each result was replicated; a positive-control procedure ruled out the possibility that the effect of the field was a product of the method of analysis. Measurements performed while the rabbits were under anesthesia suggested that the effect was mediated by N-methyl-D-aspartate and/or alpha(2)-adrenoceptors. No differences were found between exposed and control epochs in any animal when the experiment was repeated after the rabbits had been killed, indicating that a putative interaction between the field and the EEG electrodes could not account for the observed effects. We conclude that EMF transduction resulting in changes in brain electrical activity could be demonstrated consistently using a nonlinear method of analysis.

Animals↗

PubMed2003

Nonlinear changes in brain electrical activity due to cell phone radiation.

We studied the effect of an electromagnetic field from a cellular telephone on brain electrical activity, using a novel analytical method based on a nonlinear model. The electroencephalogram (EEG) from rabbits was embedded in phase space and local recurrence plots were calculated and quantified using recurrence quantitation analysis to permit statistical comparisons between filtered segments of exposed and control epochs from individual rabbits. When the rabbits were exposed to the radiation from a standard cellular telephone (800 MHz band, 600 mW maximum radiated power) under conditions that simulated normal human use, the EEG was significantly affected in nine of ten animals studied. The effect occurred beginning about 100 ms after initiation of application of the field and lasted approximately 300 ms. In each case, the fields increased the randomness in the EEG. A control procedure ruled out the possibility that the observations were a product of the method of analysis. No differences were found between exposed and control epochs in any animal when the experiment was repeated after the rabbits had been sacrificed, indicating that absorption of radiation by the EEG electrodes could not account for the observed effect. No effect was seen when deposition of energy in the brain was minimized by repositioning the radiating antenna from the head to the chest, showing that the type of tissue that absorbed the energy determined the observed changes in the EEG. We conclude that, in normal use, the fields from a standard cellular telephone can alter brain function as a consequence of absorption of energy by the brain.

Action Potentials↗

PubMed2003

Localization of electroreceptive function in rabbits.

The detection process by which animals react to the presence of electromagnetic fields (EMFs) may be a form of sensory transduction. However, the anatomic location of signal transduction in most species is unknown. Attempts to solve this problem by applying local EMFs and registering the resulting changes in the electroencephalogram (EEG) have not succeeded because of the nonstationarity of the EEG and the insensitivity of linear methods of analysis. We approached the problem of localizing electroreception in rabbits by using recurrence quantification analysis (RQA), a novel method of nonlinear analysis designed to detect small deterministic changes in a larger signal irrespective of considerations involving stationarity. When 2.5 G, 60 Hz was applied to the entire body, increased determinism in the EEG was found in all 10 animals studied, as evidenced by statistically significant increases in two RQA quantifiers. A similar result occurred when the field was applied only to the front half of each animal, but no effect on the EEG was seen when the field was applied only to the back half. When the field was localized to the head, the effect on the determinism in the EEG was again seen. When the field was further localized to the eye, the effect did not occur. Overall, the results indicated that detection of the field occurred in cells or extracellular structures in the head, probably the brain, although the methods used did not have the resolution to discriminate between specific brain structures. Thus, our results showed that the presence of transient deterministic brain states induced by an EMF signal could be documented using dynamical analysis, thereby allowing us to infer the approximate anatomic location of the signal's transduction.

Animals↗

PubMed2002

Consistent magnetic-field induced dynamical changes in rabbit brain activity detected by recurrence quantification analysis.

The reports dealing with the effects of electromagnetic fields (EMFs) on brain electrical activity have been inconsistent. We suspected that the use of linear methods and models accounted for some of the variability, and we explored the issue by using a novel approach to study the effects of EMFs on the electroencephalogram (EEG) from rabbits. The EEG was embedded in phase space and local recurrence plots were calculated and quantified to permit comparisons between exposed and control epochs from individual animals. Statistically significant alterations in brain activity were observed in each animal (n=10) when it was exposed to 2.5 G, 60 Hz, as assessed using each of two recurrence-plot quantifiers. Each result was replicated; a positive-control procedure ruled out the possibility that the effect of the field was a product of the method of analysis. Measurements performed while the rabbits were under anesthesia suggested that the effect was mediated by N-methyl-D-aspartate and/or alpha(2)-adrenoceptors. No differences were found between exposed and control epochs in any animal when the experiment was repeated after the rabbits had been killed, indicating that a putative interaction between the field and the EEG electrodes could not account for the observed effects. We conclude that EMF transduction resulting in changes in brain electrical activity could be demonstrated consistently using a nonlinear method of analysis.

Algorithms↗

PubMed2002

Comparison of tests of accommodation for computer users.

BACKGROUND: With the increased use of computers in the workplace and at home, optometrists are finding more patients presenting with symptoms of Computer Vision Syndrome. Among these symptomatic individuals, research supports that accommodative disorders are the most common vision finding. METHODS: A prepresbyopic group (N= 30) and a presbyopic group (N = 30) were selected from a private practice. Assignment to a group was determined by age, accommodative amplitude, and near visual acuity with their distance prescription. Each subject was given a thorough vision and ocular health examination, then administered several nearpoint tests of accommodation at a computer working distance. RESULTS: All the tests produced similar results in the presbyopic group. For the prepresbyopic group, the tests yielded very different results. CONCLUSION: To effectively treat symptomatic VDT users, optometrists must assess the accommodative system along with the binocular and refractive status. For presbyopic patients, all nearpoint tests studied will yield virtually the same result. However, the method of testing accommodation, as well as the test stimulus presented, will yield significantly different responses for prepresbyopic patients. Previous research indicates that a majority of patients prefer the higher plus prescription yielded by the Gaussian image test.

Accommodation, Ocular↗

PubMed2002

The efficacy of computer glasses in reduction of computer worker symptoms.

BACKGROUND: Computer workers with presbyopia are at greater risk for the development of symptoms with a conventional prescription vs. a computer prescription because general-wear multi-focal corrections often do not provide adequate correction for the viewing distances and angles needed at the computer workstation. "Computer glasses," as defined by the American Optometric Association, are specifically designed for the computer workplace and have a different lens design or prescription than general-wear glasses. The purpose of this study is to evaluate the effectiveness of computer glasses in reduction of symptoms of presbyopic computer users. METHODS: Subjects were 26 symptomatic presbyopic computer users who had had an eye examination within the past year and had 20/20 vision at distance and near with habitual glasses. Two interventions in planned alternating order were tested for 3 weeks each on all subjects. One intervention was computer glasses. The comparison intervention was an ergonomic self-assessment tool (ESAT) with their habitual Rx. Symptoms were assessed before and after each intervention. A post-comparative questionnaire asked subjects to reflect on the relative efficacy and ease of use of the two interventions. RESULTS: The computer glasses were significantly more effective at reducing the frequency and severity (p < 0.008) of the symptoms than the ESAT, and 24 of 26 subjects judged the computer glasses to bemore effective. Subjects attributed 80.7% of symptom reduction to the computer glasses and 19.3% to the ESAT. Although the ESAT was judged effective, it was not as effective as the computer glasses. CONCLUSION: Computer glasses have been shown to be effective in reduction of vision-related symptoms of computer users.

Computers↗