ORIGINAL PAPER 31 P-MRS Using Visual Stimulation Protocols with Different Durations in Healthy Young Adult Subjects Felipe R. Barreto • Thiago B. S. Costa • Ricardo C. G. Landim • Gabriela Castellano • Carlos E. G. Salmon Received: 9 July 2014 / Revised: 29 August 2014 / Accepted: 8 September 2014 / Published online: 17 September 2014 Ó Springer Science+Business Media New York 2014 Abstract Phosphorus magnetic resonance spectroscopy ( 31 P-MRS) combined with visual stimulation in functional experiments allows the non-invasive dynamic study of brain energy metabolism. 31 P-MRS has been applied to several diseases and to healthy subjects, but works have shown variable findings and non-reproducible results, possibly caused by low numbers of subjects combined with different stimulation paradigms. In the present work, we used 31 P-MRS at 3 T with two different visual stimulation protocols with different block duration (‘‘short’’ and ‘‘long’’) to evaluate metabolic changes under different workloads in 38 healthy subjects. We found a 15 % (short protocol—blocks of 1.5 min stimulation) and 3 % (long protocol—blocks of 5 min stimulation) increase in the inorganic phosphate (Pi) to a-adenosine triphosphate (a-ATP) ratio, and a 5 % (short protocol) and 2 % (long protocol) decrease in the nicotinamide adenine nucleotide (NADH ? NAD ? ) to a-ATP ratio. The NADH ? NAD ? results are, to the best of our knowledge, the first functional magnetic resonance spectroscopy in vivo assessment of these compounds, but their interpretation is difficult since they cannot be separately quantified at 3 T. Our results show that longer stimulations produce smaller concentra- tion changes in Pi/a-ATP and (NADH ? NAD ? )/a-ATP ratios, which suggests a possible adaptation effect during longer stimulations that leads metabolic concentrations towards the initial equilibrium. Keywords Energy metabolism Á NADH Á Inorganic phosphate Á Phosphorus magnetic resonance spectroscopy Á Visual stimulation Introduction Phosphorus magnetic resonance spectroscopy ( 31 P-MRS), combined with visual stimulation in functional experi- ments, allows the non-invasive study of high energy phosphates in the human brain. It is well known that adenosine triphosphate (ATP) hydrolysis is the main energy source of the human brain, produced by the com- plete oxidation of glucose. During high ATP demand in the muscle, the increase of adenosine diphosphate (ADP) leads to a shift in the balance of the creatine kinase (CK) reac- tion, causing a fall in the phosphocreatine (PCr) concen- tration, which is responsible for providing the phosphorus atoms to convert ADP into ATP again [1]. Besides PCr and ATP (a-ATP, b-ATP, c-ATP), coenzyme NAD ? , and its reduced form NADH, can be detected as a single resonance by 31 P-MRS at 3 T. NAD ? is involved in redox reactions, playing an important role in oxidative metabolism by transporting electrons between reactions [2]. 31 P-MRS can be also used to quantify pH from chemical shift difference between resonances [3], and these quantities may provide additional metabolic information. F. R. Barreto Á C. E. G. Salmon (&) Department of Physics, Faculdade de Filosofia, Cie ˆncias e Letras de Ribeira ˜o Preto, Universidade de Sa ˜o Paulo, Av. Bandeirantes 3900, Monte Alegre, Ribeira ˜o Preto, SP 14040901, Brazil e-mail: garrido@ffclrp.usp.br F. R. Barreto Á T. B. S. Costa Á R. C. G. Landim Á G. Castellano Á C. E. G. Salmon CInAPCe Program (Cooperac ¸a ˜o Interinstitucional de Apoio a Pesquisas sobre o Ce ´rebro), Sa ˜o Paulo, Brazil T. B. S. Costa Á R. C. G. Landim Á G. Castellano Neurophysics Group, Departamento de Cronologia, Instituto de Fı ´sica Gleb Wataghin, Raios Co ´smicos, Altas Energias e Le ´ptons, Universidade de Campinas (UNICAMP), Rua Se ´rgio Buarque de Holanda 777, Cidade Universita ´ria, Campinas, SP 13083859, Brazil 123 Neurochem Res (2014) 39:2343–2350 DOI 10.1007/s11064-014-1433-9