On March 31, 2014, the second phase of the John Edward Porter Neuroscience Research Center was dedicated. This new facility is shared by scientists from the National Institute of Neurological Disorders and Stroke (NINDS), National Eye Institute (NEI), National institute of Child Health and Human Development (NICHD), National Institute of Dental and Craniofacial Research (NIDCR), National institute of Mental Health (NIMH), National Institute on Deafness and Other Communicable Disorders (NIDCD), and the National Institute of Biomedical Imaging and Bioengineering (NBIB)—and represents a unique opportunity for scientists to collaborate across academic disciplines as well as the boundaries that sometimes separate institutes and centers on the NIH campus.
A new wave of research and exploration is beginning within these walls with new support for the creation of a new arsenal of instruments for unlocking the mysteries of the brain through the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative. This moment may be the most appropriate to look back over the accomplishments of the last century and anticipate those of the next.
Ricardo Martínez Murillo, Ph.D., Director of the Instituto Cajal in Madrid, Spain, is pictured in front of NIH's recently dedicated neuroscience research center where the exhibition of Ramón y Cajal original drawings is located.
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Cajal’s law of dynamic polarization, wherein information flows from the receptive dendrites of a neuron through its cell body and down through its axon (and on through the dendrites of the cells with which it forms synapses), is well illustrated in this figure above comparing the visual and olfactory systems. The olfactory and visual systems were integral to Cajal’s formulation of the law of dynamic polarization, since it was clear where the external stimulus originated and in which direction information ought to flow. Cajal was thus able to hypothesize that the dendrites (or, in photoreceptors, the pigmented outer segments) of the receptor neurons, which were closest to the stimulus, serve a receptive function, and thus, that the axons must be responsible for passing the information onwards. The olfactory system is shown in Fig 1: information originates in the olfactory mucosa (B), where olfactory receptor neurons (a) sense environmental stimuli and send signals to the olfactory bulb (A), which sends it further on to the olfactory cortex (C). This information transfer is unidirectional – signals originating in the olfactory cortex and relayed back to the olfactory bulb travel along a separate set of neurons (e,f,g). Similarly, in the visual system (Fig 2), information travels in the retina from the photoreceptors (a,m), through the bipolar cells (b,n) and ganglion cells (c,o) through the optic nerve to higher visual centers (B). Cajal showed that, in birds, information originating higher in the visual system travels back to the retina along a separate set of neurons (p,q,r).
Among his many “firsts,” Ramon y Cajal was the first to analyze the structure of individual neurons in the cingulate cortex, a structure in the brain involved with emotion formation and processing, learning, and memory. In this drawing, Cajal highlights the structure of the anterior cingulate cortex, as well as its surrounding tissues, the induseum griseum (right D), the cingulum bundle (left D), and the corpus callosum (E).
While the layers of structure are intended to be the same on each side of the drawing, on the left side, Cajal emphasizes the pyramidal neurons present in the five cortical layers of the anterior cingulate cortex (1-5), while on the right side, he draws attention to the interneurons found in those layers (a, d). In addition to the variety of types of pyramidal neurons that comprise the cingulate cortex (extroverted, small, medium, large, fusiform), there are also a variety of non-pyramidal neurons (multipolar, bipolar, and bitufted).
The soma of the neurons and interneurons are mainly in layers 2-5, while layer 1 is made of a dense arbor of dendrites from the layers below. Changes in the number, density, or composition of neurons in the anterior cingulate cortex are associated with disease states such as Parkinson’s disease, Alzheimer’s disease, and schizophrenia.
