About 2,600 years ago the pre-Socratic school of thought emerged (Collective, 1988). Without marching noisily through the streets, these philosophers showed a crucial freedom of thought. They abandoned mythology to anchor themselves to reason. The poetic narrative that was supposed to explain the world was gradually replaced by arguments and demonstrations. It was at the core of this current of thought that Anaximandre de Milet (“Anaximander”) tried, unabated, to explain the origin and organization of all facets of the world from a scientific point of view. He put aside gods and goddesses for the benefit of cause and consequence, coherence and demonstration.
Anaximander was the first to publish a map of the world with the aim of representing the ecumene: all the lands inhabited by man. This is obviously not by chance. To embark on the path of knowledge requires above all to be able to locate it. And what other way do we have than to map ?
In our previous article on the fly’s prowess, citing the work of Trush and his colleagues, we noted that the cerebral cortex of the fruit fly revealed a column structure with the ability to analyze the visual scene. It turns out that this column structure is precisely the one that allows the fly to… map its visual environment.
The cortex is, by definition, the part that forms the envelope of the animal or plant’s organ. For the brain, the cerebral cortex is a layer of neurons that shape its surface. It is of greyish appearance and found in flies, mice, giraffes and humans. The cerebral cortex is divided into many sections with different territories providing a well-identified function. For the human cortex, the three main areas are defined as: the motor, sensory and associative areas.
If you stimulate a region in the motor area, a part of the body will move. And conversely, if you move a part of the body, the zone of the corresponding motor area will activate. This is visible on an MRI. The cerebral cortex is remarkable in that it is also organized by the thickness of its cortical columns. Look at the illustration image: a 3D reconstruction of cortical columns of a rodent’s cerebral cortex. These so-called “barrel” columns mainly process information obtained from a mustache on the animal’s snout. Touch a single mustache and the corresponding cortical column of the rodent will activate.
For all those who try to understand the processing of the signal performed by the brain, this organization of cortical columns is a true Grail. Formally established by numerous works, including those of Lorente de No, reveal that the nervous system is organized into modules. This applies not only to vertebrates, of which we belong, but also to invertebrates, dreadful creatures, soft and repugnant (Lourente de No., 1938).
The cerebral cortex is therefore not an interlacing of complex neurons that is quasi-inextricable. It is like a modern, modular city, with its streets and avenues allowing local or long-distance transport between neighborhoods. Understanding how the cerebral cortex works begins by understanding how its modules work. This is a more accessible task, though it remains of course extremely difficult to accomplish. But not impossible.
The study of anatomy gives us a serious boost but it does not tell us anything about what is happening in the cortical columns. What signals do they receive, what process do they use and finally what are they for?
It was almost by chance that the answer was provided by two young researchers David Hubel and Torsten Wiesel. Their job was to record the activity of neurons in the cat’s visual area by trying to find out which orientation of a light signal was capable of increasing their electrical activity. Their account speaks for itself: “When we first undertook this type of experiment in 1961, the result was so surprising that we found it hard to believe. Instead of a series of random orientations, we found a sequence of a stunning order. Each time the electrode advanced, even 25 to 50 micrometers, the optimal orientation [of visual stimulus] changed by a small angular step of ten degrees on average; each step succeeded the other in the same direction, either clockwise or in the opposite direction” (Hubel-Wiesel,1962) (Hubel-Wiesel, 1978).
In other words, Hubel and Wiesel discovered that the cortical columns in the cat’s visual area detects the orientation of the light signals in an orderly manner: two nearby columns in the cat’s visual cortex detect signals in close proximity. And what goes for the cat, goes for the fly. This won them both the Nobel Prize in 1981.
Let’s remember Anaximander: mapping is the start of knowing. Mapping is to represent the environment’s elements on a map all the while respecting their proximity as much as possible. This is exactly what the visual cortex of the fly does. And we will later see that it is a principle common to all sensory modalities and to all living beings.
But the question that will now concern us relates to the mechanism that creates this order: auto-organization. How is it able to achieve this feat? It’s a promise, our next article will describe how it works and especially how you can do it.
References
Collectif. (1988). Les Présocratiques (éd. Bibliothèque de La Pléiade, Vol. 345). (J.-P. Dumont, Éd.) NRF.
HubeI, D. H., & Wiesel, T. N. (1978). Les mécanismes cérébraux de la vision. Belin.
Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields binocular interaction and functional architecture in the cat ‘s visual cortex. Journal of Physiology, 160, 106-154.
Lorente de No, R. (1938). The cerebral cortex: architecture, intracortical connections and motor projections. (J. Fulton, Éd.) Physiology of the nervous system, 291-301.