Nets without nodes and vice versa: The paradoxical Golgi and Cajal story
In 1873 Camillo Golgi wrote to a friend these words: «I spend long hours at the microscope. I am delighted that I have found a new reaction to demonstrate even to the blind the structure of the interstitial stroma of the cerebral cortex. I let the silver nitrate react with pieces of brain hardened in potassium dichromate. I have obtained magnificent results and hope to do even better in the future». This was the first reference to the discovery of the brain reaction which allowed the staining of single nerve cells. By applying this method to different part of the brain and spinal cord, Golgi elaborated a reticularist theory of brain structure and function also named diffuse nervous net, according to which the axons prolongations of nerve cells were fused or interlaced in a diffuse web along which the nervous impulse propagated. Even if the idea of a net of mutual relationship among the nervous elements, was not absent before Golgi, the novelty of his model was his functional penchant. According to Golgi, in fact, the diffuse nervous net was a physiological organ, in which the nervous impulse travels diffusely, establishing a not-selective communication system linking together every part of the encephalon and the spinal cord. The direct consequence of this model was that, according to Golgi, large part of the brain could function in an ensamble, i.e. in a holistic way. In fact he affirmed that brain activity was due «not to the isolated action of individual cells but to the simultaneous activity of large group of cells».
Golgi’s model was probably the first, in the history of science, that clearly related a complex function to a concept of net, i.e that related a web of relationship among nerve cells to the astonishing complexity and flexibility of nervous activity.
Towards the end of the nineteenth century this concept developed in polemical opposition to the neuron theory championed by the Spanish histologist Santiago Ramón y Cajal which affirms that the nervous system is anatomically and functionally composed of individual cells, like any other tissue, and that nerve cells act to each other through points of contact subsequently named synapses. In advocating this theory Cajal assumed an anti-reticularist view as a general epistemological approach to the brain function. It is obvious to say that the net of Golgi was wrong and that the neuronal concatenations of Cajal, at synaptic level, are a fairly good approximation to reality. But if we consider these models from a general “neurophilosophical” point of view we can see that both deal with one of the two fundamental aspects of neurosciences. In fact if there are two words that can epitomize more than any others, the basic pillars of neurosciences these two words are: net and nodes. Net means that the basic elements of the nervous system are related through a diffuse web of circuital relationships working both in a series and parallel to each other, accounting for the complexity of the nervous function. But they must also be targeted specifically. This second requisite is assured by specific nodes, i.e. synapses.
Now, from a historical point of view, if we look at the origin of the neurosciences, we find a paradoxical situation. Golgi advocated the idea that the functional level accounting for the activity of the encephalon and the spinal cord has to be searched in a net of mutual relationship among nerve cells. On the contrary Cajal assumed that this fundamental functional level has to be found at the synaptic level and the idea of a net conceived as physiological element is substantially absent from his writings.
Thus we reach the paradoxical conclusions that the two fundamental concepts of brain organization, the net and the nodes, were endorsed with mutual exclusion by the two champions of early neurosciences.
Pavia, Italy, 2006