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Training the Train of Ideas "When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased. This is often paraphrased as "Neurons that fire together wire together." It is commonly referred to as Hebb's Law. The combination of neurons which could be grouped together as one processing unit, Hebb referred to as 'cell-assemblies'. And their combination of connections made up the ever-changing algorithm which dictated the brain's response to stimuli." "5. Some of our ideas have a natural correspondence and connexion one with another; it is the office and excellency of our reason to trace these, and hold them together in that union and correspondence which is founded in their peculiar beings. Besides this, there is another connexion of ideas wholly owing to chance or custom: ideas, that in themselves are not at all of kin, come to be so united in some men's minds that it is very hard to separate them, they always keep company, and the one no sooner at any time comes into the understanding but its associate appears with it; and if they are more than two which are thus united, the whole gang, always inseparable, show themselves together." (336)  "6. This strong combination of ideas, not allied by nature, the mind makes in itself either voluntarily or by chance, and hence it comes in different men to be very different, according to their different inclinations, educations, interests, etc. Custom settles habits of thinking in the understanding, as well as of determining in the will, and of motions in the body: all which seem to be but trains of motion in the animal spirits, which, once set a-going, continue in the same steps thay have been used to; which, by often treading, are worn into a smooth path, and the motion in it becomes easy and, as it were, natural. As far as we can comprehend thinking, thus ideas seem to be produced in our minds; or, if they are not, this may serve to explain their following one another in an habitual train, when once they are put into that track, (—tengo que hacer un inciso para recalcar que las metáforas ferroviarias de Locke no son tales, claro; está pensando más bien en caminos de mulas alisados por el constante uso. Pero tan adecuada es la metáfora que podría darle ideas adicionales a algún ingeniero, o a algún neurólogo). as well as it does to explain such motions of the body. A musician used to any tune will find that, let it but once begin in his head, the ideas of the several notes of it will follow one another orderly in his understanding, without any care or attention, as regularly as his fingers move orderly over the keys of the organ to play out the tune he has begun, though his unattentive thoughts be elsewhere a-wandering. Whether the natural cause of these ideas, as well as of that regular dancing of his fingers, be the motion of his animal spirits, I will not determine, how probable soever, by this instance, it appears to be so; but this may help us a little to conceive of intellectual habits and of the tying together of ideas." "7. That there are such associations of them made by custom in the minds of most men, I think nobody will question who has well considered himself or others; and to this, perhaps, might be justly attributed most of the sympathies and antipathies observable in men, which work as strongly and produce as regular effects as if they were natural; and are therefore called so, though they at first had no other original but the accidental connexion of two ideas, which either the strength of the first impressions or future indulgence so united that they always afterwards kept company together in that man's mind, as if they were but one idea. I say most of the antipathies, I do not say all: for some of them are truly natural, depend upon our original constitution, and are born with us; but a great part of those which are counted natural would have been known to be from unheeded, though perhaps early, impressions or wanton fancies at first, which would have been acknowledged the original of them, if they had been warily observed. A grown person surfeiting with honey no sooner hears the name of it, but his fancy immediately carries sickness and qualms to his stomack, and he cannot bear the very idea of it; other ideas of dislike and sickness and vomiting presently accompany it, and he is disturbed, but he knows from whence to date this weakness and can tell how he got this indisposition: had this happened to him by an overdose of honey when a child, all the same effects would have followed, but the cause would have been mistaken, and the antipathy counted natural." (337) "No es nuestro ánimo exponer aquí las diversas teorías propuestas para explicar ese fenómeno de transformación de un acto consciente en inconsciente; seános lícito, sin embargo, indicar la conjetura que juzgamos más racional y armónica con los datos de la evolución ontogénica. Comencemos por afirmar, de acuerdo con muchos fisiólogos, que para que una excitación pueda llegar al campo de la consciencia, es condición indispensable que alcance cierta intensidad y además que en la corteza cerebral, teatro del fenómeno consciente, concurran ciertas condiciones físico-químicas todavía desconocidas que se traducen en lo dinámico por el despertar de la atención. Esto sentado, puede admitirse que, durante la época juvenil, es decir, antes del modelamiento definitivo de las arborizaciones nerviosas, las ramas colaterales sensitivo-motrices poseen un desarrollo relativamente limitado, marchando las corrientes de preferencia por los tallos ascendente y descendente, y alcanzando fácilmente el bulbo (ganglios de Goll y de Burdach) y la corteza cerebral á la que llegan con energía bastante para causar una reacción consciente. Mas, ulteriormente, y a consecuencia del ejercicio, las colaterales se hipertrofian á expensas de las terminales que permanecerán, en cuanto á grosor, más ó menos estacionarias; de donde se sigue que la excitación sensible, por su tendencia natural a propagarse en el sentido de la menor resistencia, fluirá ahora de preferencia por las colaterales. Por consiguiente, bajo un estímulo periférico moderado, al cerebro llegará solamente una corriente débil incapaz de provocar la sensación á menos que por los mecanismos puestos en juego por la atención, es decir, congestionando y aumentando la excitabilidad de la corteza gris no surja el hecho de consciencia y las consiguientes reacciones motrices intencionales. En otros términos: no es que la onda sensitiva ascendente sea en el adulto incapaz de provocar reacciones conscientes, sino que para determinarlas necesita, ó alcanzar intensidad mayor que en la edad juvenil, ó hallar la corteza cerebral convenientemente preparada para ello. Las preferencias de ruta á que aludimos, podrían todavía exagerarse merced á un superior desarrollo (por ramificación y estiramiento) de las arborizaciones protoplásmico-nerviosas, es decir, por un creciente aumento de la superficie de contacto de las neuronas constitutivas del arco excito-motor. (Textura del sistema nervioso del hombre y de los vertebrados, I, xix, 456). "Nadie ignora que la obra de un pianista, de un orador, de un matemático, de un pensador, etc., resulta absolutamente inabordable para el hombre ineducado, cuya adaptación al nuevo trabajo (caso de que concurran en el sujeto circunstancias orgánicas favorables) es obra de muchos años de gimnasia mental y muscular. Para comprender este importante fenómeno se hace necesario admitir, además del refuerzo de las vías orgánicas preestablecidas, el establecimiento de otras nuevas, mediante la ramificación y crecimiento progresivo de las ramificaciones dendríticas y nerviosas terminales. En tal suposición, el talento adquirido (dejando a un lado lo relativo á la capacidad cerebral ó memoria orgánica, cuantía de neuronas y otras condiciones que deben influir también en el resultado), tendría por principal condición la presencia de centros conmemorativos primarios y secundarios provistos de enlaces múltiples y complicados entre órdenes ó pléyades neuronales poco ó nada relacionadas en los cerebros incultos. Por virtud de esta superior asociación, una excitación sensorial ligera, la contemplación de una idea, un estímulo, en fin, cualquiera incapaz de provocar en un cerebro ineducado sino asociaciones vulgares ó ilógicas, suscitaría en las cabezas fuertemente cultivadas é impresionables, combinaciones ideales inesperadas, que traducen esquemática, pero fielmente, relaciones positivas de la realidad exterior, y se condensan y expresan en fórmulas generales y fecundas. La citada hipótesis explicaría también: la memoria lógica, es decir, ese encadenamiento y subordinación ordenada de las adquisiciones, que no se logra sino tras largo esfuerzo de atención y reflexión, y mediante una nueva organización de los centros conmemorativos; así como la creación de sistemas arquitectónicos de ideas ó construcciones lógicas complicadas (sistemas ó credos filosóficos, religiosos y políticos). Las observaciones y argumentos que sirven de apoyo á esta hipótesis son: 1º Durante el desarrollo embrionario, las dendritas y ramificaciones nerviosas se extienden y ramifican progresivamente, poniéndose en contacto con un número cada vez mayor de neuronas (véase Histogénesis de la médula espinal, capítulo XXI, tomo I). 2º Es un hecho también que el ajuste definitivo de estas relaciones no se verifica sino después de algunos tanteos, advirtiéndose que antes de que las expansiones lleguen á su destino y creen articulaciones estables, desaparecen numerosas ramas accesorias, especie de asociaciones de ensayo cuya existencia prueba la gran movilidad inicial de las arborizaciones celulares." (Textura del sistema nervioso del hombre y de los vertebrados, II.2, xlviii, 1150-51). "A stimulation implies a force added to, or evolved in, that part of the organism which is its seat; while a mechanical movement implies an expenditure or loss of force in that part of the organism which is its seat: implying some tension of molecular state between the two localities. Hence if, in the life of a minute animal, there are circumstances involving that a stimulation in one particular place is habitually followed by a contraction in another particular place—if there is thus a repeated motion through some line of least resistance between those places; what must be the result as respects the line? If this line—this channel—is affected by the discharge–if the obstructive action of the tissues traversed, involves any reaction upon them, deducting from their obstructive power; then a subsequent motion between these two points will meet with less resistance along this channel than the previous motion met with, and will consequently take this channel still more decidedly. Every repetition will further diminish the resistance offered; and thus will gradually be formed a permanent line of communication, differing greatly from the surrounding tissue in respect of the ease with which force traverses it. Hence in small creatures may result rudimentary nervous connexions." (First Principles 211-212) "Only an adumbration of nervous processes thus hinted as conforming to the general law, is here possible. But the effects of associations between impressions and motions as seen in habits, all yield illustrations. In knitting, in reading aloud, in the performance of the skilled pianist who talks while he plays, we have examples of the way in which channels of nervous communication are eventually made so permeable by perpetual discharges along them as to bring about a state almost automatic or reflex: illustrating at once the fact that molecular motion follows lines of least resistance, and the fact that motion along such lines, by diminishing the resistance, further facilitates the motion." (212) "Al igual que el repetir la asociación entre dos ideas facilita la excitación de una por parte de la otra, del mismo modo cada descarga de sentimientos en forma de acciones vuelve más fácil una descarga subsiguiente de tales sentimientos en tales acciones" (456).
Miércoles, 28 de Septiembre de 2011 18:33. José Ángel García Landa Enlace permanente. Ciencia y tecnología Comentarios » Ir a formulario |
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