Théodule Ribot, answered from the texts and cited to the page.
In the dissolution of the mind there is a law, and it is the mirror of development. Whatever is formed last is undone first; whatever is most complex, most voluntary, most delicately organized, is the most fragile; whatever is oldest, simplest, most automatic, most deeply organized, resists longest.1 So in the diseases of memory the recollections of yesterday vanish while those of childhood remain, the proper names before the common, the ideas before the feelings, the voluntary recall before the habits the hand and tongue perform without thought; the old man losing his memory travels backward through his life.2
So too the will dissolves from its highest coordinations down to mere impulse, and the personality unravels from its latest acquisitions toward its organic base. Destruction does not fall at random. It retraces, step by step and in reverse, the very order in which the mind was built — for what evolution has laid down last and lightest, dissolution takes away first.345
The law of decay, in psychology, consists in a continuous retrogression, descending from the higher to the lower, from the complex to the simple, from the unstable to the stable, from the most to the least organised; in other words, those manifestations which are the latest in date of evolution are the first to disappear; while those which were the first to appear are the last to vanish.The Psychology of the Emotions
If it were possible for a given period of time to compare in humanity, taken as a whole, the total number of acts produced by voluntary attention with the total number of those produced without it, the ratio would be nearly as zero to infinity.Diseases of the Will, p. 122
I regret my inability to place before the reader more facts of this kind, notwithstanding an extended search. GENERAL AMNESIA. 127 When attention is called to tMs point, I hope that other material will be discovered. On the whole, our law, derived from facts and verified by observation, may be assumed as true until the contrary is proved. It may be further corroborated by other known facts.Diseases of Memory, pp. 137–139
The rapidity with which the patient learns shows that all was not lost. The cells may have been atrophied but, if their nuclei (generally considered as the seat of reproduction) give origin to other cells, the bases of memory are re-established; the new cells resemble the parent-ceUs by virtue of that tendency of every organism to maintain its type, and of every acquired modification to transmit its characteristics…Diseases of Memory, pp. 212–213
It does not come from above, but from below; it is a sublimation of inferior elements. I would compare volition, once affirmed, to what is called in architecture the keystone of an arch. To it the arch owes more than its solidity,: its existence; but this stone derives its power wholly from the others which sustain it and shut it in, as in its turn it presses upon them and holds them in place.Diseases of the Will, pp. 114–116
Ribot's Law of regression is his most famous generalization and entered neurology and psychiatry as a lasting clinical principle, framed by Spencer's evolution-dissolution and Jackson's neurology. It captures real and robust phenomena — the temporal gradient of retrograde amnesia (recent memories more vulnerable than remote), the pattern of loss in Alzheimer's dementia, the survival of overlearned and procedural memory — and "Ribot's gradient" is still invoked. But as a strict universal law it is an idealization that real data only partly fit: the temporal gradient of amnesia is debated and depends on the lesion and the type of memory, retrograde amnesia has complex non-monotonic patterns, and frontal versus temporal damage produces different profiles. So the law is a powerful, partly-confirmed clinical generalization rather than an exceptionless natural law.