What is thinking? That inquiry can be approached in many ways: physiologically, psychologically, phenomenologically, etc. But I would argue that none shed light on thinking in the way physiology does. This text is written with a purpose to consolidate my understanding of the ideas from a seminal tractate "Reflexes of the Brain"[1] by the brilliant physiologist Ivan Sechenov first published in 1863. I hope that it will serve as a kind of summary and that the reader may also find it interesting.
Sechenov starts with a simple but deep assumption:
The infinite diversity of external manifestations of cerebral activity can be reduced ultimately to a single phenomenon — muscular movement. (1)
He further divides all muscular movements into two groups: involuntary and voluntary. And attempts to show that all of them might be reduced to series of reflexes. Where the term reflex stems from the fact that the excitation of the sensory nerve is reflected in the motor nerve. Every reflex is further divided into three phases: sensory (afferent), integrative (central) and motor (efferent).
Observing how involuntary muscular movements work in frogs he concludes on their nature, "All involuntary movements are mechanical in origin." Meaning all of them are reducible to reflexes. Further he attempts to show that not only involuntary movements can be reduced to reflexes, but that voluntary movements (including the sense of free will and agency) are also of that nature. But most interestingly he comes to the hypothesis on what constitutes thinking.
He opens up the analysis of voluntary movements with the following observation:
I shall try to show in a few words that the final component of any voluntary act — muscular movement — is essentially identical with the activity of muscles in pure reflexes, i.e., in elementary involuntary movements. Physiology maintains that there are no special motor nerves and muscles for voluntary movements. The same nerves and muscles which produce the purely involuntary movements act also in the case of voluntary movements.
… Consequently, that part of the reflex mechanism which consists of the motor nerve and muscle is likewise capable of producing voluntary movements.
He further elaborates on the development of voluntary movements from the cradle. Emphasizing the fact that in each case, be it visual or aural perception or any other, the movements initially involved in its development are involuntary in nature and acquired by repetition. Child attempts to focus on most pronounced visual or aural stimuli involuntarily and many times until control over corresponding muscular movements is developed. He basically derives the concept of attractor (he calls it "notion") by observation and analysis and describes how it is formed through differentiation with repetition based on involuntary movements of a child. Which gives him confidence to declare that psychical processes are reflexes in nature and developed from involuntary movements. And although they are of complex nature (represented by series of associations formed in memory with repetition) their roots as reflexes may be derived from initially involuntary movements.
After the analysis of child's development he makes the following assumption:
This capacity of the sense organs to perceive external influences in the shape of sensations, to analyse the later in time and in space, and to combine them fully or partially into diverse groups is the sum total of the means which govern man's psychical development.
This assumption is stronger than (1) but follows from his observations and analysis. It is rather the exclusion of unnecessary postulates, the Occam's razor of sorts. He references Helmholtz's works on analysis of aural and visual senses and generalizes from there to other senses. It gives him confidence to analyze operations of the senses and postulate how notions and concepts are developed in the brain. Thus equivalencing psychical processes with reflex mechanism. To recapitulate, involuntary movements that are reflexes in nature lead to the development of psychical processes, such as notions and concepts, and hence psychical processes are reducible to reflexes as well, he calls them psychical reflexes.
Notably he reduces the development of notions of time and space to the operation of the senses and particular muscular movements.
Actually, sound and muscular sensation alone give man the idea of time — and not by their entire content, but by one element only, namely, the duration of the sound and the muscular sensation. A certain object is moving before my eyes; following this object I gradually move either head or eyes, or both; in each case the visual sensation is associated with a protracted sensation of the contracting muscles; I say "the movement is durable like a sound".
… Visual and purely tactile memory can be described as memory of space, while aural and muscular memory can be described as memory of time.
In the end of analysis of the development of voluntary movements he stresses out the following facts:
A reflex always ends in movement, which is invariably accompanied by muscular sensation.
… From the standpoint of the process, there is not the slightest difference between an actual impression with its consequences and the memory of this impression.
… By now the reader will have an idea of the importance of frequent repetition of one and the same act for psychical development. Repetition is the mother of learning, i.e., of a better differentiation of all psychical formations.
… All psychical acts without exception, if they are not complicated by elements of emotion (we shall dwell on these elements later) develop by way of reflex. Hence, all conscious movements resulting from these acts and usually described as voluntary, are reflex movements in the strict sense of the term.
What concerns emotions and desires he also successfully reduces them to reflex mechanism. Therefore through experiments on inhibitory mechanisms in frogs (stimulation of the midbrain could suppress spinal reflexes), analysis of the development of the brain from the cradle and a series of assumptions he comes to a conclusion that all movements — involuntary and voluntary — are just reflexes. That is an important thing to consider, which paves the way for a description of what is thinking. He also makes a profound observation which will help to understand the latter part:
When a child thinks, it at the same time inevitably speaks.
That is, the child has not learned to inhibit the motor phase of the reflex. Sechenov then turns to the investigation of inhibition of muscular movements. Noticing that inhibition shuts down the third phase of a reflex, namely the motor phase. And shows that such inhibition (just as any muscular movement) has to be learned. That is shutting down the motor phase of a reflex has to be learned as any other skill.
Man must learn to control the inhibition of movements just as he learns to perform the movements themselves.
… The child's ability to inhibit movements, or, strictly speaking, to eliminate the last member of a reflex, is acquired by learning.
He also highlights the fact that the capacity to inhibit the last member of a reflex is difficult to develop.
From this example the reader will gather that the muscular sensations accompanying the inhibition of movements are really weak. The fact that teachers cannot develop in their pupils the capacity to paralyse the external manifestations of their psychical activity must be attributed precisely to this circumstance. This also explains why this capacity is rarely encountered in man and why persons possessing it are, to a degree, regarded as freaks of nature.
And the following paragraph is the crux of Sechenov's investigation on what is thinking:
I shall now show the reader the first and most important result of man's capacity to inhibit the last member of a reflex. This can be summarized as the ability to think, meditate and reason. What, actually, is the process of thinking? It is the series of interconnected notions and concepts which exists in man's consciousness at a given time and which is not expressed in external manifestations resulting from these psychical acts. But a psychical act, as the reader knows, cannot appear in consciousness without an external sensory stimulation. Consequently, thought is also subordinated to this law. It manifests, therefore, the beginning of a reflex and its continuation; only the end of the reflex, i.e., movement, is apparently absent.
A thought is the first two-thirds of a psychical reflex.
That is a groundbreaking statement in many ways. First, it shows that the capacity for the inhibition is a skill just like any other. Second, it implies that all voluntary acts such as thinking are really reducible to reflexes in nature, thus wiping out the free will dilemma. What he writes further elucidates these results.
Thought is generally accepted as a cause of [voluntary] action. When the external influence, i.e., the sensory stimulus, remains unnoticed — which occurs very often — thought is even accepted as the initial cause of action. Add to this the strongly pronounced subjective nature of thought, and you will realise how firmly man must believe in the voice of self-consciousness when it tells him such things. But actually this is the greatest of falsehoods: the initial cause of any action always lies in external sensory stimulation, because without this thought is inconceivable.
It implies that the sense of agency which we experience (i.e. "I" as a conscious agent that makes choices out of its own volition independent of external stimuli and initiates action) is but a fabrication. All actions are initiated by some external stimuli, even if this is a complex reflex involving many associations and stored in memory, the cause for such series of reflexes to fire is external sensory stimulation of some sort. And the narrative which thinking weaves for itself (i.e. that it has made a choice to write these letters) is just a post hoc illusory construct. Further what concerns conscious choice:
Given the same internal and external conditions the activity of man will be similar. Choice of one of the many possible ends of the same psychical reflex is absolutely impossible; its apparent possibility is a merely a delusion of self-consciousness.
That is, given the same conditions one could not have behaved differently. So thoughts like, "I could have done otherwise", are fictions of self-consciousness. To paraphrase it further, choices are made constantly (i.e. reflexes compete) but they what we might say unconscious without anyone controlling them. The conscious part just gets updates from the unconscious mechanism (this predates Libet's experiments[2], and his later introduction of "free won't" does not hold ground because the inhibition also develops by way of reflex). There is no magical entity that affects the behavior beyond the reflex mechanism. That is, again, a repudiation of the ideas of free will and agency.
This however does not imply that the behavior of an individual may become chaotic and irresponsible in view of such knowledge. Conscience and the moral sense are developed just like any other sense: by cultivating feelings for goodness, example, proper social contract and repetition. They have nothing to do with free will. Among many competing motives the stronger wins. Therefore, it depends on the innate traits and upbringing which will it be. The absence of free will does not undermine the value of goodness, integrity, honesty, reliability and strong ethos. On the contrary, it removes the unnecessary and harmful belief that any action is possible at any time without the proper work behind it.
To sum up, I find these results truly illuminating (especially considering the year when they first appeared). To answer the question "what is thinking?" — thinking is a capacity to inhibit the last phase of a reflex (the motor phase). It is a skill like any other that can be learned. And the much wider implication — all voluntary movements are reducible to reflexes. Therefore, free will and the sense of agency are just illusory constructs which thinking builds for itself as an intermediary (integrative) step of reflex process. And these constructs may be deconstructed[3] as unnecessary.
Ivan Sechenov, Selected Physiological and Psychological Works.
Gary Weber, Myths about Nonduality and Science.