Learning and Memory Changes Associated with Exposure to Radio and Low Frequency Electromagnetic Fields
By @SamoaSilk
Abstract
This review takes into consideration the neurobehavioral consequences of low-frequency (LF) and radio-frequency electromagnetic field (RF-EMF) exposure. Electromagnetic frequency pollution has been associated with science fiction despite having the capability of inducing biological changes. Here, research demonstrating behavioral disorder resulting from frequencies of both low-level and radio emissions will be evaluated. The origin of these fields will be discussed primarily in terms of wireless communication devices. Non-radiation related factors associated with wireless device usage are also taken into consideration. The correlation between radiation exposure and changes in sleep quality, memory processes, and hormone production is discussed.
Discovering Electromagnetic Fields
Electromagnetic fields (EMFs) are capable of inducing currents within the human body (Akdag et al., 2016). The physiological changes in the body that result from EMFs depend on their frequency, amplitude, and the duration in which the body is exposed. According to the International Commission on Non-Ionizing Radiation Protection (2009), high level frequency radiation (HLF-EMF) emissions have the potential for cellular and DNA damage. Lower level frequencies, such as those emitted from household appliances, have not been shown to cause this kind of damage. Though, there is evidence that exposure to lower level power frequency magnetic fields increases the risk of childhood learning disabilities through disruption of nocturnal production of melatonin in the pineal gland (Dyche, Anch, Fogler, Barnett, & Thomas, 2012), and that exposure may alter REM sleep latency, a stage of sleep that is necessary for sleep consolidation (Mohammed, Fahmy, Radwan, & Eslayed, 2013). The goal of this paper is to investigate whether extremely low frequency EMFs (ELF-EMFs) and radiofrequency EMFs (RF-EMFs) have influence on learning and memory behavior via disruption of brain activity, particularly during sleep.
Classification of EMFs
The electromagnetic spectrum includes both natural and human made sources of EMFs. EMFs are a fascinating area of research; while there are therapeutic applications of EMFs, the detrimental side effects of long-term exposure of various frequencies are not well understood. The various classifications of EMF can be broken down into simple terms. ELF-EMFs generally have frequencies up to 300 Hz, intermediate frequency (IF) fields range from 300 Hz to 10 MHz, and radiofrequency (RF) fields have frequencies of 10 MHz to 300 GHz (Figure 1).
Figure 1. Kheifets, Repacholi, Saunders, & van Deventer’s (2005) Table of EMFs.
Childhood Vulnerability to EMF Exposure
ELF-EMF. As countries around the world continue to develop, human exposure to EMFs between 0 to 300 GHz continues to rise as a result of the demand to generate and distribute electricity (Redlaski, 2015). Evidence of an association between ELF-EMF exposure and childhood leukemia has brought attention to the potential harmful effects of EMF emissions (Redlaski, 2015). This association was acknowledged by the International Agency for Research on Cancer (IARC), which later classified ELF-EMF as a “possible human carcinogen” (IARC, 2002). The evidence for this was established through studies using cancer patients and control subjects who were examined by their proximity to power lines. A correlation between leukemia and brain cancer in children was observed in these studies, however there are little studies with a sophisticated assessment of exposure therefore further research is needed (Kundi, 2007; IARC, 2002). The IARC suggests that there is a possibility that children have higher levels of sensitivity compared to adults toward radiation; however it is unclear whether this is true for some or all segments of the EMF spectrum (IARC, 2002).
RF-EMF. An expert group in the United Kingdom was the first to raise concerns about the potential vulnerability of children to RF-EMF given the rising use of wireless mobile devices (Kheifets, Repacholi, Saunders, & van Deventer, 2005). The rational that children may be more sensitive stemmed from the notion that children have a longer lifetime of exposure in comparison to adults; additionally, children have a developing nervous system with brain tissue that is more conductive than that of adults (Kheifets, Repacholi, Saunders, & van Deventer, 2005). Increased conductivity results from a higher water content and ion concentration in the brain; this results in greater absorption of RF energy emitted by wireless devices within brain tissue (Kheifets, Repacholi, Saunders, & van Deventer, 2005).
EMF and Brain Cancer
Central nervous system (CNS) tumors account for approximately 20% of recorded growths in children under the age of 15 years old, but account for less than 2% in adults (Kheifets, Repacholi, Saunders, & van Deventer, 2005). This is because CNS tumors during childhood commonly develop mesodermal or embryonic tissues of origin, whereas epithelial tissues (cerebral hemispheres) are often cancerous in adults (Kheifets, Repacholi, Saunders, & van Deventer, 2005). Brainstem gliomas (a malignant, or very infectious cancer) are often the diagnosis made in children (Kheifets, Repacholi, Saunders, & van Deventer, 2005). In 2011, the World Health Organization (WHO) and the IARC qualified EMFs emitted by mobile phones as a risk to glioma development (Kheifets, Repacholi, Saunders, & van Deventer, 2005). Rises in childhood CNS tumor diagnosis have been observed in the United Kingdom, Japan, Australia, and the United States within the last few decades (Kheifets, Repacholi, Saunders, & van Deventer, 2005). Epidemiologic studies suggest there is risk of childhood leukemia associated high levels of ELF-EMF exposure, however laboratory studies have yet to explain how EMF influence cellular division in mesodermal or embryonic tissues (Kheifets, Repacholi, Saunders, & van Deventer, 2005).
Current State of Research
While it is documented that HF-EMF can cause cellular and DNA damage (Akdag et al., 2016), ELF-EMF and RF-EMF are in need of additional research.
ELF-EMF. Zhang, Liu, Zhang, and Li (2015) studied the short-term effects of ELF-EMF on Alzheimer’s disease (AD) in twenty male Sprague Dawley rats. AD was modeled in the rat by injection of amyloid-beta (Aβ) content in the hippocampus. Rats were randomly divided into exposure group (50Hz ELF-EMF) or sham exposure at 12 weeks. Association between ELF-EMF exposure and memory impairment was investigated. After 12 weeks of exposure, cognitive and memory ability was tested using a Morris water maze. Results failed to identify a causational relationship between ELF-EMF exposure and cognition and memory impairments in rats. The researchers noted that more comprehensive studies are still required to clarify their findings, and that the possible effects and mechanisms of ELF-EMF exposure on living organisms were still unknown (Zhang, Liu, Zhang, & Li, 2015). Aβ plaques were detected unchanged in the cortex; ELISA assays were used to measure hippocampus and plasma. H&E staining was used to detect neuron morphology. Short-term ELF-EMF exposure did not alter Aβ expression or neuron morphology, however the researchers suggest that long-term studies are necessary (Zhang, Liu, Zhang, & Li. 2015).
RF-EMF. In RF-EMF studies, DNA damage is generally not observed as a result of exposure (Akdag et al., 2016). Rats that undergo long-term exposure (2.4 GHz RF-EMF (via Wi-Fi)) do not show DNA damage, however the testes had shown to be an organ that is sensitive to exposure (Akdag, et al. 2016). While the testes are not directly associated with learning and memory processes, there seems to be a biological effect from RF-EMF exposure.
Can EMFs Rightfully be Classified as Dangerous?
It is unclear whether RF-EMF and ELF-EMF can be classified as dangerous. The opinions of researchers regarding the influence of EMF pollution on living organisms are divided. Existing studies suggest EMF emissions are harmless; in fact, various EMFs have medical applications. Cameron, Markov and Hardman (2014) have shown that therapeutic ELF-EMF treatment has the potential to significantly suppress tumor growth in mice. Tumor suppression can be seen with 10 minutes of ELF-EMF (120 Hz) exposure twice a day after 12 days in mice (Cameron, Markov, & Hardman, 2014). The tumor of interest was a murin 16/C mammary andocarcinoma cell growth derived from breast tissue, which was inserted hypodermically between the scapula bones in C3H mice. Cameron and colleagues (2014) observations suggest that therapeutic EMF is a possible treatment for tumor cancer patients, particularly breast cancer, which is not a concern amongst children. It is certain that ELF-EMF has the potential to cause biological effects.
EMF pollution. Various forms of EMF are associated with different phenomena that are observable in radiation exposure studies (Redlarski et al., 2015). Modern technological advancements have led to an omnipresent source of electromagnetic pollution; in many areas, this pollution generates EMF or electromagnetic radiation (EMR) that exceeds what natural sources are capable of producing (Redlarski et al., 2015). There is no conclusive evidence that this pollution causes harm to human beings; the increasing abundance of EMF emissions, however, gives reason for investigation (Redlarski et al., 2015).
Mobile devices and base stations. A base station can be defined as a local low power wireless transmitter that works as a radio signal receiver and transmitter (e.g. Wi-Fi router or cell tower). The rising number of mobile phones reflects a similar increase in the number of base stations (Sorgucu & Develi, 2012). Sorgucu and Devili (2012) successfully mapped measured radiation over a university campus by plotting 80 base stations by their power density via data entry in the Golden Software Surfer 9 program. Short term exposure to base station level radiofrequency (RF-EMF) has been shown to cause headache, irritation and difficulties concentrating among school children 8-17 years of age (Heinrich, Thomas, Heumann, von Kries, & Radon, 2010). Some base stations have higher EMF levels than others; therefore it is important to select location wisely before installation (Sorgucu & Develi, 2012). Limits set by international organizations do not provide safety against potential health risks (Sorgucu & Develi, 2012). The harm of base stations is still under investigation; studies of the distance of base stations from the point of human exposure may be used to investigate regional health problems (Sorgucu & Develi, 2012).
Learning, memory and language processing. EMF and RF-EMF exposures may instigate a chronic state of homeostatic disturbance, much like that observed in symptomatic autism or cognitive impairment (Sage & Burgio, 2017). Sage and Burgio (2017) discovered a significant relationship between the frequency and duration of phone calls made (via cell phone) with risk of ADHD in children. RF-EMF exposure may disturb neural synchrony, which may result in disordered memory and learning processes (Sage & Burgio, 2017).
Hippocampus and denate gyrus. Maskey et al. (2010) reported learning and language processing deficits in young mice associated with 835 MHz (cell phone) exposure. This was discovered by examining the effect of 325 MHz on the hippocampal region of the CA1, CA3, and denate gyrus. The dentate gyrus is a region of the hippocampus/hippocampal formation that is believed to assist in forming new episodic memories (Maskey et al., 2010). The CA1 and CA3 were chosen, as they are hippocampal areas associated with context dependent extinction, and the CA1 is believed to be responsible for context dependent memory retrieval (Maskey et al., 2010). These three regions were imunostained with calbindin (CB) and calretinin (CR). The results indicated that there was a layer specific distribution of CB and CR throughout all three regions of interest. The hippocampus is responsible for behavioral and cognitive function, particularly special learning and memory via calcium concentration fluctuation (Maskey et al., 2010). Behavioral changes such as increased anxiety and risk taking were observed.
A loss of pyramidal cells in the CA1 area was observed after 1 month of 835MHz EMF exposure; this finding was more evident in female rats and those treated during prenatal periods (Maskey et al., 2010). EMF exposure has been shown to result in shrunken, scattered or grouped dark neurons, which often lack internal structures (Maskey et al., 2010). Maskey et al. (2010) did not identify cell loss in the denate gyrus, however a study by Odaci and Kaplan (2008) found that prenatal exposure of 900MHz leads to denate gyrus cell loss in 4 week old rats. Maskey and colleagues concluded that the loss of pyramidal and interneurons detected in the CA1 region was likely due to neuronal cell death instigated by radiation. The consequences of this cell death may alter hippocampal GABAA and GABAB receptor responses via modification of inhibitory control of neuronal synchronization that occurs within different behavioral states (Shetty and Turner, 1998). Pyramidal cells serve as important source of output from the hippocampus; they project connections to the orbital, medial temporal, and medial frontal cortexes (Maskey et al., 2010). Thus, the loss of pyramidal cells will diminish the connection between cortical areas and the CA1 region, which may explain behavioral manifestations (Maskey et al., 2010). Neuronal loss in the CA1 region such as this could change the hippocampal trisynaptic circuit (relays hippocampal synaptic transmission via granule cells and CA1/CA3 pyramidal neurons), which might result in learning and memory deficit (Maskey et al., 2010). With this finding in mind, Maskey and colleagues hypothesized that 835 MHz EMF may influence Ca2+ concentrations, thus the effects on the human cerebrum should be investigated as it plays a significant role in signal transduction.
Figural memory. Schoeni, Roser, and Rossli (2015) investigated whether adolescent memory performance is affected by wireless device RF-EMFs. It was tested whether implications result from RF-EMF exposure or by non-radiation related wireless device use on its own. It is important to rule out non-radiation factors such as texting, playing repetitive games, scrolling, or any task that requires little use of memory and minimal effort in retaining attention; this is done in order to determine whether it is the way we interact with our phones or the emissions that are responsible for a behavioral change. An association between RF-EMF doses and figural memory was found; a change in memory performance over one year was negatively associated with cumulative duration of cell phone usage and more strongly with RF-EMF dose. These results suggest that RF-EMF dose positively correlates with poor figural memory performance over time. Figural memory entails a combination of visual comprehension with verbal recall, however the objects themselves do not require recollection to the extent that pronunciation holds significance. Essentially, figural memory involves obligating visually presented images to memory and recognizing them as words, and this process may be altered in the presence of RF-EMFs (Dyche, Anch, Fogler, Barnett, & Thomas, 2012; Schoeni, Roser, & Rossli, 2015).
ELF-EMF
Sleep and memory consolidation theory. Research today concerning ELF-EMF’s mechanism of action often investigates the possible influence on sleep processes, particularly alteration of the circadian rhythm (internal 24-hour clock that regulates sleep and alertness) (Reiter, 1993).
The suprachiasmatic nucleus (SCN) of the hypothalamus sends signals to regions of the brain that are responsible for hormone production, body temperature, or other functions that play a roll in sleep or wakefulness. The SCN raises body temperature and releases cortisol in the early morning. The SCN is responsible for delaying release of melatonin until seep onset. Melatonin is produced by the pineal gland, which remains inactive during daytime, however in the presence of darkness melatonin is released into the blood supply. The process of melatonin production begins with L-tryptophan (precursor), which can be converted into serotonin. L-tryptophan is an amino acid that essential for creating serotonin, which is then converted to melatonin.
Melatonin. Dyche, Anch, Fogler, Barnett, and Thomas (2012) studied the effects of power frequency EMFs on melatonin and sleep in the rat. Urine analysis enabled measurement of melatonin production after 3 days of EMF (50-60Hz). The study found that such ELF-EMF exposure generally decreased melatonin synthesis of the pineal gland, which may be linked to childhood learning disabilities through insufficient cortisol levels (Dyche, Anch, Fogler, Barnett, & Thomas, 2012). This research suggests that nocturnal production of melatonin in the pineal gland can be disrupted by EMF exposure.
Conversion of serotonin. In 1993, Reiter performed a study on static (naturally occurring) EMF and ELF-EMF exposure effects on the circadian production of melatonin. (Explain, include differences in effects of static and ELF). Static EMF had been shown to disturb circadian melatonin rhythm, but alteration was not significant (Reiter, 1993). ELF-EMF had been shown to depress melatonin concentrations of the pineal gland, blood, pineal cyclic AMP levels, and hydroxyindole-O-methyltransferase activity (which is an enzyme responsible for forming melatonin) (Reiter, 1993).
REM Sleep. Mohammed, Fahmy, Radwan, and Eslayed (2013) studied non-thermal continuous and modulated EMR fields effect on sleep EEG of rats. Chronic exposure to non-thermal ELF-EMF was investigated. EEG recordings suggested that rapid eye movement (REM) sleep is more susceptible to modulated RF-EMF than slow wave sleep (SWS). Mohammed and collegues discovered that the latency of REM sleep increased in the presence of ELF-EMF exposure, this suggests that ELF-EMF has the potential to change sleep cycles. It is possible that REM sleep is more susceptible to interaction with EMF (compared to SWS) due to radio frequency interactions with the cholinergic system (which controls both REM and waking states) (Mohammed, Fahmy, Radwan, & Eslayed (2013). Given that there appears to be a clear importance of REM sleep for memory consolidation, alteration in REM sleep due to EMFs may compromise learning and memory processes.
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