A number of studies have examined various aspects of brain function in laboratory animals.

The blood-brain barrier (BBB) consists of endothelial cells tightly attached in order to protect the brain from substances in the blood that may affect its delicate function. It is a selectively permeable hydrophilic barrier. Many animal studies have examined, with conflicting results, the effects of various radiation frequencies on the exchange of molecules (e.g. calcium, albumin) across the BBB (Oscar, 1977; Salford, 1993, 1994; Saunders, 1996). Tsurita (2000) did not find any effect on the BBB or the cerebellum of rats exposed to 1,439 MHz field for one hour per day, five days per week, for up to four weeks. This paper pointed out that although some studies have shown an increase in permeability of the BBB, these results may have been dependent on thermal effects. Schirmacher and colleagues (2000), however, found that 1.8GHz EMFs increased the permeability of the BBB to sucrose, and felt that they could exclude thermal mechanisms as the explanation for this change. This group, however, improved BBB tightness and failed to reproduce their earlier findings (Franke, 2005a, 2005b). Salford (2003) reported albumin leakage and nerve cell damage in rats after 2 hours exposure to microwaves from a 915 MHz cell phone. Finnie (2002), however, found no evidence of increased albumin leakage in mice exposed to 900 MHz radiation for 1 hour, 5 days per week for 2 years. Similarly, Cosquer (2005) could not find any effect of EMFs on the BBB. Nylund (2004) found evidence to suggest that RFR exposure at 900 MHz frequency for 1 hour could change the expression of proteins that are involved in the structure of the cell. He postulates that this could weaken the blood-brain barrier. Kuribayashi (2005) failed to detect any changes in the BBB in immature and young adult rats after exposure to 1439 MHz EMFs at SAR up to 6W/kg for 90 minutes a day for 2 weeks. Finnie (2006) reported no breakdown of the BBB in neonatal mice receiving a 60-minute far-field whole body exposure of 4 W/kg on 7 successive days postnatally. Kumlin (2007) found no evidence of breakdown in the BBB in young rats exposed to a 900 MHz signal at 0.3 or 3 W/kg. 2 hours a day on 5days a week for 5 weeks.

Exposure to low level pulsed or continuous microwave radiation has been reported to affect neurotransmitter metabolism and the concentration of receptors involved in stress and anxiety response to different parts of the brain. (Lai 1992, 1994; Mausset, 2001; Testylier 2002). The Independent Expert Group on Mobile Phones in the UK pointed out that most of the studies had used high power densities that might have produced thermal effects. Cosquer (2005) reported that exposure to 2.45 GHz EMFs does not alter anxiety responses in rats. Mausset-Bonnefont (2004) reported cellular and molecular changes in rats' brains after exposure to 900 MHz RFR at a high brain-averaged SAR of 6 W/kg. Brillaud (2007) confirmed this effect. Dasdag (2004) reported that exposure of rats to 900 MHz RFR had no effect on brain structure and fatty acid composition, but affected malondialdehyde concentration. The latter is a measure of lipid peroxidation. Thorlin (2006) found no evidence of damage-related factors in glial cells exposed to RFR at SARs up to 27 W/kg.

Other studies have suggested that RF radiation can alter the electrical activity of the brain as measured by electroencephalogram (EEG) responses (Saunders, 1996). Another study (Tattersall et al., 2001) suggested that low intensity RF fields at 700 MHz can alter electrical activity in hippocampal slices from rat brain. The hippocampus is involved in spatial learning and memory processes. Beasond (2002) found that a GSM-like signal to neurons of an avian brain produced increased excitation in 52% and decreased in another 17%.

Several studies have examined cognitive function. Two studies suggested that 2450 MHz microwave radiation might influence the spatial memory of rats (Lai, 1994; Wang and Lai, 2000). However, replication studies by Cobb (2004) and Cassel (2004) failed to show an effect of 2450 MHz microwave radiation on rats' spatial memory. Sienkiewicz and colleagues (2000) found no effect of a 900 MHz field on spatial learning tasks in mice. These authors used SAR levels much lower than in Lai's experiments. Kumlin (2007) exposed young rats to a 900 MHz frequency signal for 2 hours a day, 5 days a week, for 5 weeks and found no evidence of an effect in the open-field test, plus maze test, or acoustic startle test. In the water maze test, however, they found significantly improved learning and memory. Dubreuil (2002) used a heads-only exposure to 900 MHz radiation and found no effect on spatial learning tasks in rats. Yamaguchi (2003) found no effect of 1439 MHz pulsed TDMA fields on rats' learning in a T-maze, unless the SAR was high enough to cause temperature elevation. These authors suggest that the exposure system used by Wang and Lai could produce the microwave hearing effect, thus influencing the rats' behaviour. Bornhausen (2000) examined the offspring of rats exposed throughout pregnancy to 900 MHz pulsed radiation. The average whole body SAR was between 17.5 and 75 mW/kg. There were no differences in litter size, body mass, or developmental landmarks. The offspring were tested as adults for cognitive deficits, and none were found. In a review of animal studies D'Andrea (1999) concluded that there was a threshold for the disruption of behavioural performance at a SAR of about 4 W/kg.

Exposure to amplitude-modulated low-level microwave radiation at low SAR levels has been reported to cause calcium efflux from nerve cells or brain tissue at a specific range of ELF modulation frequencies, known as frequency or power "windows" (Dutta,1984; Luben, 1996; Royal Society of Canada Expert Panel, 1999; Independent Expert Group on Mobile Phones and Health, 2000). Other studies, however, have not been able to replicate the findings using the same power windows. One study (Paulraj, 2002) reported increased calcium efflux from brain cells following exposure to 2.45 GHz continuous wave As well, continuous wave (CW) RF fields have been shown to affect the transport of cations such as sodium and potassium across cell membranes over a wide range of SARs (0.2 to 200 W/kg) and frequencies (27 MHz to 10 GHz) (Luben, 1996; Repacholi, 1998; Independent Expert Group). Platano (2007) reported that CW or GSM-modulated 900 MHz RF-EMFs do not significantly alter the current amplitude or the current-voltage relationship of Ba 2+  through voltage-gated calcium channels. However, the biophysical modeling of these effects is not sufficiently established and the implications for human health not well enough understood for human risk to be determined (Cleary, 1996; Repacholi, 1998; Independent Expert Group on Mobile Phones, 2000). Further, little information is known about the biological effects in this area at the specific frequencies used in cellular telephone communications (i.e., 800-900 MHz and about 1.9 GHz).
Hermann and Hossmann (1997), in an extensive review of neurological effects, concluded that:

The UK Independent Expert Group stated, with respect to nervous system effects:

References:

Authors
Ammari M, Brillaud E, Gamez C, Lecomte A, Sakly M, Abdelmelek H, de Seze R. (2008):
Title
Effect of a chronic GSM 900MHz exposure on glia in the rat brain.
Journal
Biomed Pharmacother. 2008 Mar 26 Ahead of print.

Authors
Ammari M, Lecomte A, Sakly M, Abdelmelek H, de-Seze R. (2008):
Title
Exposure to GSM 900MHz electromagnetic fields affects cerebral cytochrome c oxidase activity.
Journal
Toxicology. 250(1):70-74.

Authors
Beasond R C, Semm P (2002):
Title
Response of neurons to an amplitude-modulated microwave stimulus.
Journal
Neuroscience letters 33:175-8.
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Authors
Bornhausen M, Scheingraber H (2000)
Title
Prenatal exposure to 900 MHz, cell-phone electromagnetic fields had no effect on operant-behavior performances of adult rats.
Journal
Bioelectromagnetics 21:566-574.
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Authors
Brillaud E, Piotrowski A, de Seze R (2007)
Title
Effect of an acute 900 MHz GSM exposure on glia in the rat brain: A time-dependent study.
Journal
Toxicology 238:23-33.
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Authors
Cassel JC, Cosquer B, Galani R, Kuster N (2004)
Title
Whole-body exposure to 2.45 GHz electromagnetic fields does not alter radial-maze performance in rats.
Journal
Behav Brain Res 155:37-43.
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Authors
Cobb BL, Jauchem JR, Adair ER (2004):
Title
Radial arm maze performance of rats following repeated low level microwave radiation exposure.
Journal
Bioelectromagnetics 25:49-57.
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Authors
Cosquer B, Galani R, Kuster N, Cassel JC (2005):
Title
Whole-body exposure to 2.45 GHz electromagnetic fields does not alter anxiety responses in rats: a plus-maze study including test validation.
Journal
Behav Brain Res 156:65-74.
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Title
Cosquer B, Vasconcelos AP, Frohlich J, Cassel JC (2005b).
Authors
Blood-brain barrier and electromagnetic fields: effects of scopolamine methylbromide on working memory after whole-body exposure to 2.45 GHz microwaves in rats.
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Behav Brain Res 161:229-237.
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Authors
Dasdag S, Akdag MZ, Aksen F, Bashan M, et al. (2004).
Title
Does 900 MHz GSM mobile phone exposure affect rat brain?
Journal
Electromagnetic Biology and Medicine 23:201-214.
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Authors
Dubreuil D, Jay T, Edeline J-M (2002)
Title
Does heads-only exposure to GSM-900 electromagnetic fields affect the performance of rats in spatial learning tasks?
Journal
Behavioural Brain Research 129:202-210
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Authors
Eberhardt JL,  Persson BRR, Brun AE,  Salford LG, Malmgren LOG.
Title
Blood-Brain Barrier Permeability and Nerve Cell Damage in Rat Brain 14 and 28 Days After Exposure to Microwaves from GSM Mobile Phones
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Electromagnetic Biology and Medicine 2008;27( 3):215 – 229.

Authors
Finnie JW, Blumberg PC, Manavis J, Utteridge TD, et al. (2002)
Title
Effect of long-term mobile communication microwave exposure on vascular permeability in mouse brain
Journal
Pathology 34:344-347
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Authors
Finnie JW, Blumbergs PC, Cai Z, Manavis J, et al. (2006)
Title
Neonatal mouse exposure to mobile telephony and effect on blood-brain barrier permeability
Journal
Pathology 38:262-263.
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Authors
Franke H, Ringelstein EB, Stogbauer F (2005a)
Title
Electromagnetic fields (GSM 1800) do not alter blood-brain barrier permeability to sucrose in models in vitro with high barrier tightness.
Journal
Bioelectromagnetics 26:529-535.
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Authors
Franke H, Streckert J, Bitz A, Goeke J, et al. (2005b):
Title
Effects of universal mobile telecommunications system (UTMS) electromagnetic fields on the blood-brain barrier in vitro.
Journal
Radiat Res164:259-269.
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Authors
Grafström G, Nittby H, Brun A, Malmgren L, Persson BR, Salford LG, Eberhardt J.
Title
Histopathological examinations of rat brains after long-term exposure to GSM-900 mobile phone radiation.
Journal
Brain Res Bull. 2008 Sep 6 Ahead of print.

Authors
Kumlin T, Iivonen H, Miettinen P, Juvonen A, et al. (2007):
Title
Mobile phone radiation and the developing brain: Behavioral and morphological effects in juvenile rats. Journal
Radiat Res 168: 471-479.
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Authors
Kuribayashi M, Wang J, Fujiwara O, Doi Y, et al. (2005)
Title
Lack of effects of 1439 MHz electromagnetic near field exposure on the blood-brain barrier in immature and young rats.
Journal
Bioelectromagnetics 26:578-588.
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Authors
Lai H, Horita A, Guy AW (1994)
Title
Microwave irradiation affects radial-arm maze performance in the rat.
Journal
Bioelectromagnetics 15:95-104.
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Authors
Mausset A-M, de Seze R, Montpeyroux F, Privat A (2001).
Title
Effects of radiofrequency exposure on the GABAergic system in the rat cerebellum: clues from semi-quantitative immunohistochemistry.
Journal
Brain Research 912:33-46.
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Authors
Mausset-Bonnefont AL, Hirbec H, Bonnefont X, Privat A, et al. (2004):
Title
Acute exposure to GSM-900 MHz electromagnetic fields induces glial reactivity and biochemical modifications in the rat brain.
Journal
Neurobiol Dis17:445-454.
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Authors
Nylund R, Leszczynski D (2004):
Title
Proteomics analysis of human endothelial cell line EA.hy926 after exposure to GSM 900 radiation.
Journal
Proteomics 4:1359-1365.
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Authors
Odaci E, Bas O, Kaplan S.
Title
Effects of prenatal exposure to a 900 Mhz electromagnetic field on the dentate gyrus of rats: a stereological and histopathological study.
Journal
Brain Res. 16 Aug 2008 Ahead of print.

Authors
Paulraj R, Behari J.
Title
The effect of low-level continuous 2.45 GHz waves on enzymes of the developing rat brain.
Journal
Electro-Magnetobiol 2002;21:221-231
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Authors
Platano D, Mesirca P, Paffi A, Pellegrino M, et al. (2007):
Title
Acute exposure to low-level CW and GSM-modulated 900 MHz radiofrequency does not affect BA2+ currents through voltage-gated calcium channels in rat cortical neurons.
Journal
Bioelectromagnetics 28:599-607.
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Authors
Salford LG, Brun A, Eberhardt JL, Persson BR (1993)
Title
Permeability of the blood-brain barrier induced by 915 MHz electromagnetic radiation, continuous wave and modulated at 8, 16, 50 and 200 Hz.
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Bioelectrochem Bioenerg 30:293-301.
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Authors
Salford LG, Brun A, Sturesson K, Eberhardt JL, et al. (1994)
Title
Permeability of the blood-brain barrier induced by 915 MHz electromagnetic radiation, continuous wave and modulated at 8, 16, 50, and 200 Hz.
Journal
Micros Res Tech 27:535-542.
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Authors
Salford LG, Brun AE, Eberhardt JL, Malmgren L, et al.
Title
Nerve cell damage in mammalian brain after exposure to microwaves from GSM mobile phones.
Journal
Environmental Health Perspectives, Online January 29, 2003 (www.ehponline.org)
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Authors
Schirmacher A, Winters S, Fischer S, Goeke J, et al. (2000)
Title
Electromagnetic fields (1.8 GHz) increase the permeability to sucrose of the blood-brain barrier in vitro.
Journal
Bioelectromagnetics 21:338-345.
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Authors
Sienkiewicz Z, Blackwell RP, Haylock RGE, Saunders RD, et al. (2000)
Title
Low-level exposure to pulsed 900 MHz microwave radiation does not cause deficits in the performance of a spatial learning task in mice.
Journal
Bioelectromagnetics 21:151-8.
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Authors
Tattersall JEH, Scott IR, Wood SJ, Nettell JJ, et al. (2001)
Title
Effects of low intensity radiofrequency electromagnetic fields on electrical activity in rat hippocampal slices.
Journal
Brain Res 904:43-53.
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Authors
Testylier G, Tondulu L, Malablau R, Debouzy JC.
Title
Effects of exposure to low level radiofrequency fields on acetylcholine release in hippocampus of freely moving rats
Journal
Bioelectromagnetics 2002;23:249-255.
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Authors
Thorlin T, Rouquette J-M, Hamnerius Y, Hansson E, et al. (2006)
Title
Exposure of cultured astroglial and microglial brain cells to 900 MHz microwave radiation.
Journal
Radiat Res 166:409-421.
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Authors
Tsurita G, Nagawa H, Ueno S, et al. (2000)
Title
Biological and morphological effects on the brain after exposure of rats to a 1439MHz TDMA field.
Journal
Bioelectromagnetics 21: 364-371.
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Authors
Wang B, Lai H (2000)
Title
Acute exposure to pulsed 2450-MHz microwaves affects water-maze performance of rats.
Journal
Bioelectromagnetics 21:52-6
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Authors
Yamaguchi H, Tsurita G, Ueno S, Watanabe S, et al. (2003)
Title
1439 MHz pulsed TDMA fields affect performance of rats in a T-maze task only when body temperature is elevated.
Journal
Bioelectromagnetics 24:223-230.
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Authors
Yan JG, Agresti M, Zhang LL, Yan Y, Matloub HS (2008): 
Title
Upregulation of specific mRNA levels in rat brain after cell phone exposure.
Journal
Electromagn Biol Med. 27(2):147-54.

Authors
Yan JG, Agresti M, Zhang LL, Yan Y, Matloub HS (2008): 
Title
Upregulation of specific mRNA levels in rat brain after cell phone exposure.
Journal
Electromagn Biol Med. 27(2):147-54.