[1] INST MEXICANO SEGURO SOCIAL, CTR MED SIGLO 21, DEPT CLIN RES NEUROL & NEUROSURG, MEXICO CITY 7, DF, MEXICO
[2] INST NACL NUTR SALVADOR ZUBIRAN, DEPT BIOCHEM, MEXICO CITY 14000, DF, MEXICO
[3] NATL AUTONOMOUS UNIV MEXICO, FAC PSICOL, DEPT PSYCHOPHYSIOL, MEXICO CITY 04510, DF, MEXICO