Recently discovered Magnesium L-threonate is the only magnesium that crosses easily the blood-brain barrier. A group of researchers from MIT showed its role in improving learning abilities and memory skills of laboratory rats (18).
There are clinical trials right now researching a possible implementation of magnesium L-threonate in treatment of dementia and Alzheimer's disease, other degenerative conditions of the human brain tissue, and also insomnia and depression.

(1) Can J Psychiatry. 2012 Feb;57(2):85-92.
Nutrient intakes are correlated with overall psychiatric functioning in adults with mood disorders.
Davison KM, Kaplan BJ.
Intersections of Mental Health Perspectives in Addictions Research Training (IMPART) Postdoctoral Research Fellow, British Columbia Centre for Excellence in Women's Health, Vancouver, British Columbia, Canada.

(2) Kardiologiia. 2012;52(9):80-6.
Magnesium in the treatment and prevention of cerebrovascular disease.
Akarachkova ES, Vershinina SV, Kotova OV.
Scientific Research Center of the First Moscow State Medical University named after I.M. Sechenov, ul. Trubetskaya 8, 199991 Moscow, Russia.

(3) Alcohol Alcohol. 2012 Nov;47(6):688-96. doi: 10.1093/alcalc/ags088. Epub 2012 Sep 7.
Association of water softness and heavy alcohol consumption with higher hospital admission rates for alcoholic liver disease.
Howarth M, Riva A, Marks P, Williams R., UK.

(4) Rocz Panstw Zakl Hig. 2012;63(2):127-34.
The influence of components of diet on the symptoms of ADHD in children.
Konikowska K, Regulska-Ilow B, Rózańska D.
Department of Dietetics, Wroclaw Medical University, Poland.

(5) Clin Calcium. 2012 Aug;22(8):1217-26.
Abnormalities of magnesium (Mg) metabolism and therapeutic significance of Mg administration in patients with metabolic syndrome, type 2 diabetes, heart failure and chronic hemodialysis.
Kikuchi K, Tanaka H, Gima M, Kashiwagi Y, Shida H, Kawamura Y, Hasebe N.
Cardiovascular Medicine, Hokkaido Cardiovascular Hospital, Sapporo, Japan.

(6) Nutr J. 2012 Jun 13;11:41. doi: 10.1186/1475-2891-11-41.
Correlation of magnesium intake with metabolic parameters, depression and physical activity in elderly type 2 diabetes patients: a cross-sectional study.
Huang JH, Lu YF, Cheng FC, Lee JN, Tsai LC.
Graduate Institute of Ph.D. Program in Nutrition and Food Science, Fu-JenCatholic University, New Taipei City, Hsinchuang, Taiwan.

(7) Nutr Neurosci. 2012 Mar;15(2):78-84.
Plasma magnesium levels and treatment outcome in depressed patients.
Camardese G, De Risio L, Pizi G, Mattioli B, Buccelletti F, Serrani R, Leone B, Sgambato A, Bria P, Janiri L.
Institute of Psychiatry, Catholic University of the Sacred Heart, Rome, Italy.

(8) Annu Rev Nutr. 2012 Aug 21;32:55-71. Epub 2012 Mar 8.
Hypomagnesemia and inflammation: clinical and basic aspects.
Weglicki WB.
Department of Biochemistry and Molecular Biology, Division of Experimental Medicine, The George Washington University School of Medicine and Health Sciences, Washington, DC 20037, USA.

(9) Clin Interv Aging. 2012;7:51-4. Epub 2012 Feb 16.
Correcting magnesium deficiencies may prolong life.
Rowe WJ.
Medical University of Ohio at Toledo, Ohio, USA.

(10) J Water Health. 2012 Mar;10(1):161-9.
Association of blood pressure and metabolic syndrome components with magnesium levels in drinking water in some Serbian municipalities.
Rasic-Milutinovic Z, Perunicic-Pekovic G, Jovanovic D, Gluvic Z, Cankovic-Kadijevic M.
Department of Endocrinology, Zemun Clinical Hospital, Belgrade, Serbia.

(11) Clin Sci (Lond). 2012 May;122(9):397-407.
Endothelial cells and magnesium: implications in atherosclerosis.
Maier JA.
Dipartimento di Scienze Cliniche L. Sacco, Università di Milano, Via G.B. Grassi 74, Milano, Italy.

(12) Neurosciences (Riyadh). 2011 Oct;16(4):320-3.
Relation between serum magnesium level and migraine attacks.
Talebi M, Savadi-Oskouei D, Farhoudi M, Mohammadzade S, Ghaemmaghamihezaveh S, Hasani A, Hamdi A.
Department of Neurology, Tabriz University of Medical Sciences, Tabriz, Iran.

(13) Neuropharmacology. 2012 Jan;62(1):304-12. Epub 2011 Aug 4.
Magnesium deficiency induces anxiety and HPA axis dysregulation: modulation by therapeutic drug treatment.
Sartori SB, Whittle N, Hetzenauer A, Singewald N.
Department of Pharmacology and Toxicology, Institute of Pharmacy, and Centre for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Peter-Mayr-Strasse 1, A-6020 Innsbruck, Austria.

(14) J Assoc Physicians India. 2011 Jan;59:19-22.
Hypomagnesemia in critically ill medical patients.
Limaye CS, Londhey VA, Nadkart MY, Borges NE.
Department of Medicine, TN Medical College and BYL Nair Ch. Hospital, Mumbai, India.

(15) Arch Intern Med. 2011 Aug 8;171(15):1391-2. Epub 2011 May 9.
Hypomagnesemia and proton pump inhibitors: below the tip of the iceberg.
Furlanetto TW, Faulhaber GA.
Division of Internal Medicine, Hospital de Clinicas de Porto Alegre, Rio Grande do Sul, Brazil.

(16) Nutr Neurosci. 2011 Jan;14(1):10-24.
Effect of magnesium chloride on psychomotor activity, emotional status, and acute behavioural responses to clonidine, d-amphetamine, arecoline, nicotine, apomorphine, and L-5-hydroxytryptophan.
Iezhitsa IN, Spasov AA, Kharitonova MV, Kravchenko MS.
Department of Pharmacology, Volgograd State Medical University, Research Institute of Pharmacology, Volgograd, Russia.

(17) Magnes Res. 2010 Dec;23(4):158-68. Epub 2011 Jan 4.
Magnesium supplementation improves indicators of low magnesium status and inflammatory stress in adults older than 51 years with poor quality sleep.
Nielsen FH, Johnson LK, Zeng H.
United States Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, North Dakota 58202-9034, USA.

(18) Neuron. 2010 Jan 28;65(2):165-77.
Enhancement of learning and memory by elevating brain magnesium.
Slutsky I, Abumaria N, Wu LJ, Huang C, Zhang L, Li B, Zhao X, Govindarajan A, Zhao MG, Zhuo M, Tonegawa S, Liu G.
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

(19) J Neurosci. 2011 Oct 19;31(42):14871-81.
Effects of elevation of brain magnesium on fear conditioning, fear extinction, and synaptic plasticity in the infralimbic prefrontal cortex and lateral amygdala.
Abumaria N, Yin B, Zhang L, Li XY, Chen T, Descalzi G, Zhao L, Ahn M, Luo L, Ran C, Zhuo M, Liu G.
Tsinghua-Peking Center for Life Sciences, School of Medicine, Tsinghua University, 100084 Beijing, China.