I began my research career in 1976 at the Cajal Institute, under the supervision of Dr. J. Rodrigo, experimentally and morphologically studying the sympathetic and parasympathetic innervation of the mammalian oesophagus. Having presented my doctoral thesis in 1980, I joined the laboratory of Drs F. Valverde and A. Fairén at the same Institute. It was in this period that I began to study the microorganization of the cerebral cortex, using the combined method of Golgi-electron microscopy, a subject that has remained the focal point for my research since then. During this period, we developed a very simple and effective method for correlative light and electron microscopic studies to analysis the connections between identified neurons at the electron microscopy level. This method allowed us to identify unequivocally every part of the axon and the dendrites of the cell under study. In 1983, I obtained a Fogarty Fellowship (NIH) to work with Dr. Edward Jones at the Washington University School of Medicine, St. Louis (USA). This allowed me to extend my studies on cortical organization through the use of additional methods, such as high resolution immunocytochemistry and the use of anatomical tracers. One of the most important scientific achievements was the demonstration of the coexistence of neuropeptides (somatostatin, neuropeptide Y and cholecystokinin) with a classical neurotransmitter (GABA) in the cerebral cortex. From 1984 to 1985 I was appointed as a Visiting Scientist, in the laboratory of Dr. Jones at the University of California (Irvine). After this period in the laboratory of the Dr. Jones (1983-1986), I obtained a Tenured in Neuroscience at the Cajal Institute to continue my research on the cerebral cortex. Between 1989 and 1991, I returned to Dr. Jones’ laboratory to study the microorganization of the monkey cerebral cortex. In 1991 I returned to the Cajal Institute to establish a research group that principally focuses on the microorganization of the normal cerebral cortex (including hippocampus) in various species (particularly humans) and on the alterations of cortical circuits in epilepsy and Alzheimer disease. In 2000, I was appointed as Research Scientist, and in 2004 as Full Professor in the same institution. Another of my principal interest is the study of the history of our current understanding of cortical organization and function. In particular, I am interested in the roots of cortical histology and circuitry. At present I am director of the Laboratorio Cajal de Circuitos Corticales (Centro de Tecnología Biomédica, UPM) and of the Laboratorio de Microorganización de la Corteza Cerebral Normal y Alteraciones de los Circuitos (Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal, CSIC).