Self Comes to Mind

of cerebral cortex, one also realizes why the idea of brain maps is not a far-fetched metaphor. One can sketch patterns onto such a grid, and when one squints a little and lets the imagination roam free, one can picture the sort of parchment paper that Henry the Navigator probably pored over when he was planning the voyages of his captains. One big difference, of course, is that the lines in a brain map are not drawn with quill or pencil; they are, rather, the result of the momentary activity of some neurons and of the inactivity of others. When certain neurons are “on,” in a certain spatial distribution, a line is “drawn,” straight or curved, thick or thin, a pattern distinct from the background created by the neurons that are “off.” Another big difference: the lead map-making horizontal layer is stacked between other layers above and below; each main element of the layer is also part of a vertical array of elements, namely, a column. Each column contains hundreds of neurons. Columns provide inputs to the cerebral cortex (the inputs come from elsewhere in the brain, from peripheral sensory probes such as the eyes, and from the body). Columns also provide outputs toward the same sources and carry out varied integrations and modulations of the signals being processed at each locality.
    Brain maps are not static like those of classical cartography. Brain maps are mercurial, changing from moment to moment to reflect the changes that are happening in the neurons that feed them, which in turn reflect changes in the interior of our body and in the world around us. The changes in brain maps also reflect the fact that we ourselves are in constant motion. We come close to objects or move away from them; we can touch them and then not; we can taste a wine, but then the taste goes away; we hear music, but then it comes to an end; our own body changes with different emotions, and different feelings ensue. The entire environment offered to the brain is perpetually modified, spontaneously or under the control of our activities. The corresponding brain maps change accordingly.
    A current analogy to what goes on in the brain relative to a visual map can be found in the sort of picture you see in electronic billboards, in which the pattern is drawn by active or inactive light elements (light-bulbs or light-emitting diodes). The analogy to electronic maps is all the more apt because the content depicted in them can rapidly change merely by changing the distribution of active versus inactive elements. Each distribution of activities constitutes a pattern in time. Different distributions of activity within the same patch of visual cortex can depict a cross, or a square, or a face, in succession or even in superposition. The maps can be rapidly drawn, redrawn, and overdrawn, at the speed of lightning.
    The same kind of “drawing” also happens in an elaborate outpost of the brain called the retina. It too has a square grid ready to inscribe maps. When the light particles known as photons strike the retina in the particular distribution that corresponds to a specific pattern, the neurons activated by the pattern—say, a circle or a cross—constitute a transient neural map. Additional maps, based on the original retinal map, will be formed at subsequent levels of the nervous system. This is because the activity at each point in the retinal map is signaled forward along a chain, culminating in the primary visual cortices while preserving the geometrical relationships they hold at the retina, a property known as retinotopy.
    Although the cerebral cortices excel at the creation of detailed maps, some structures below the cerebral cortex are able to create coarse maps. Examples include the geniculate bodies, the colliculi, the nucleus tractus solitarius, and the parabrachial nucleus. The geniculate bodies are dedicated, respectively, to visual and auditory processes. They too have a layered structure ideal for topographical representations. The superior colliculus is an important provider of visual maps and even has the ability to relate those visual maps to auditory and body-based maps. The inferior colliculus is dedicated to auditory processing. The activity of the superior colliculi may be a precursor of the mind and self processes that later blossom in the cerebral cortices. As for the nucleus tractus solitarius and parabrachial nucleus, they are the very first providers of whole-body maps to the central nervous system. The