In this book, Bryant translated and collected major commentaries and explanations of the famously brief and sometimes cryptic sutras by Patanjali. I especially find his approach of mixing certain Sanskrit keywords in the text to be instructive. In these instances, the non-interchangeability between Sanskrit concepts and their (supposedly) corresponding English words is palpable. Despite sharing the Indo-European roots, the non-translatability is probably due to the massive distance in time.
It is hard to overstate the vast theoretical context behind the brevity of this manual. I am crawling my way through it slowly, and every few pages I am surprised by the deep insight into human psychology that was gleamed by the ancient Indian scholars and practitioners. I am in awe of these insights, not necessarily as a source of mysticism or exotic wisdom, but rather by the exhaustive and sophisticated examination of ... neurological patterns of the human mind.
Take for example the concept of citta, which refers to an organ that provides three types of functions: buddhi (roughly translated as intelligence), ahankara (the sense of self, I-ness, ego), and manas (the part of the mind that performs thinking and sensory processing).
Looking at these three components, one cannot help but be struck by their accuracy in describing some of the major activities of the brain. In the most basic aspect, it is now well established that one of the major functions of the brain is to centrally process and interpret the excitatory signals transmitted from the peripheral nerves (ie, manas), which allows humans to perceive and react to the environment. This neurological discovery in modern medical science was fairly recent and based on the anatomical exploration and understanding of the nervous system. The definition of buddhi, which emphasizes discernment and judgment, largely matches what is referred to as the executive function in neuroscience, which is carried out by the prefrontal cortex.
Of course, I am by no means saying the ancient Indian theory of the brain is complete or comparable to modern neuroscience. Several other types of brain functions that we now know are not described in this theoretical system, such as the emotional and instinctive activities in the limbic system and the structure and activities related to learning and memory (the hippocampus and more). Their technologies and research framework did not allow the ancients to realize that major bodily functions, such as body temperature, breathing, and heart rate, are linked to the brain stem. Nevertheless, I am greatly impressed by how far they had gone using only direct and empirical observations of the mind. The power of their self observation is astounding and unparalleled. (Perhaps this is in some ways related to the pursuit of "detachment", but that's a topic for another day.)
The examination of the sense of self is particularly fascinating and sophisticated. Recently I am intermittently reading a book by the German psychiatrist Fritz Simon, in which he explains how every concept is defined by what is inside versus outside a border (ie, what it is versus what it is not). It is a difficult and abstract concept that I have a hard time grasping and have never seen described in basic psychological theories. Yet the ancient Indians realized that the human mind (or what is now widely referred to as "consciousness", a fashionable and self-aggrandizing buzzword since the 2000s) is self-referential.
Another eerily accurate insight is that the brain's existence is proven through its constant activities, defined as vrttis. The ancient Indians asserted that our endless thoughts, feelings, reactions, dreams, and spontaneous, internally generated sensations, are the manifestations of a physical organ that is alive and working. This insight alone outstrips Descartes by hundreds or a thousand years. The Indian philosophers explained it in an elegant analogy: Citta is the sea, and vrttis is the waves.