Hierarchical Brain

Introduction

“I am a brain, Watson. The rest of me is a mere appendix.” Sherlock Holmes in “The Adventure of the Mazarin Stone” by Arthur Conan Doyle

This is the introduction to a set of web pages that is my attempt to describe how the human brain works by breaking down the explanation into seven hierarchical levels of description. Most of the content is not new; I have used and linked together many well-established theories from different areas of neuroscience, psychology and philosophy, but I have also found the need to use some new ideas and concepts of mine. This set of web pages describes a model for thinking about how the brain works that I hope may provide some insights and suggest some new possibilities for research. For more on this, see the background to these pages.

This page outlines the main proposals of this website and has a small number of links to other introductory pages. For links to lower-level pages that provide full details and references, please see the summary page. Because it is a high-level introduction, this page includes some over-simplifications that are explained and clarified in more detail in the lower-level pages. For information about how these pages are formatted and linked together, see the structure of this website. More concise overviews can be found on the home page or the abstract page. There is also a simple summary, intended for children or for people who are learning English.

• The human brain is a very complex and very remarkable organ
  • The human brain is self-configuring, self-balancing and self-generating (i.e. it generates a “self”).
    • The brain of a human baby creates huge numbers of connections between neurons very early in life. Input from the senses, as well as internal activity, tunes and prunes these connections over time, self-configuring the brain into one that is capable of processing data in a cumulative and hierarchical way.
    • The process of tuning and pruning also ensures that a balance is kept between excitation and inhibition, and therefore also between activity and inactivity, whilst maintaining a whole-brain network.
    • Over time, the cumulative and hierarchical processing creates representative symbols, not only of things and concepts outside the body, but also of the body and the processes of the brain itself.
    • Eventually, the concept of the “self” is generated, a self that is capable of perceiving and feeling.
    Remarkably, all of this happens solely because of the characteristics of the lowest-level components, the neurons and synapses, with help from glial cells; the difficulty lies in explaining the gap between the functionality of these low-level components and the internal feelings that I experience.
  • The human brain has evolved over hundreds of millions of years, from a few nerve cells in a tiny organism that have a small number of connections and provide simple reflex reactions, to a brain that contains billions of nerve cells, trillions of connections and controls a human body and all its organs as well as the gamut of human behaviour.
    • The brain has had to evolve in order to control a much larger and more complex body that has itself evolved over millions of years.
    • It has also had to evolve to react to the changing physical and social environments in which the evolving body has found itself.
    • Throughout all this time and all these changes, the primary aim of the brain has always been to allow the body to survive and reproduce.
    This is not intended to imply that the current human brain is a pinnacle of development, but it is certainly the product of a very long and complex process of evolution.
  • The DNA that is passed down the generations determines the overall structure of the brain, the major connections within it, the methods of development of a growing brain and the low-level detail of some crucial areas, but does not specify the details of connections that are largely created and updated by learning, both during development and later in life.
    • A new human brain develops from a few cells in an embryo and grows large numbers of new nerve cells with huge numbers of connections very rapidly.
    • Many structures deep within the brain, such as those that control vital bodily functions, are clearly predetermined and laid down very early in development, but nearly all other areas are much more adaptable and can potentially serve multiple purposes.
    • One particular area, the neocortex (the outer layer of the human brain), is made up of six layers within units known as columns. There are millions of these columns, and, although they are not all identical, most have similar types of connections between and within the layers, which when large numbers are connected together can form a hierarchical, tree-like structure that has both forwards and backwards connections. These columns can be regarded as standard building blocks, but other areas of the brain have similar connections as well.
    • What makes an individual brain unique are the subtle changes that are made to these connections from the very start of the development process, right up until the time of death.
    • It is these changes that allow learning to take place, and are the source of memory, experience and intelligence.
  • It is amazing that we still have so little knowledge of the workings of our own brains.
    • It is really only in the last hundred years or so that it has been generally accepted by scientists that the brain is the seat of all of a human’s learning, thinking and consciousness.
    • Most of our current knowledge of the workings of the brain has come about from research and theories from within the last fifty years or so.
    • The more we understand, the more mind-boggling it is! But it is probably still true to say that we understand far more detail about the workings of the inside of a star than the workings of the human brain!
    • The majority of the knowledge gained in the last fifty years has been from various types of high-level scans, behavioural evidence following trauma, experiments on animals, and, occasionally, experiments on humans.
    • It has proved very difficult to investigate higher-level phenomena such as consciousness and free will because they are solely personal experiences and cannot be tested in any normal scientific way.
    • There is a large explanatory gap between what we humans know about the workings of the brain and the experience that we humans have of using our brains.
  • This complexity and lack of understanding is why attempts to describe or explain the human brain from the bottom up have rarely made progress.
• Multiple levels of description are needed in any explanation of a complex object.
  • It is well known from other areas of science that a complex object can usually only be described or explained using hierarchical layers and multiple levels of description.
  • Each individual level must be describable in its own terms with explanations of any emergent features or concepts.
  • Each level should be “useful” in that it must provide new information and/or explain known observations.
  • This website outlines a hierarchical structure of levels of description that describe the working of the human brain.
  • This website itself also has a hierarchical structure, as does the brain when processing data.
  • The reason I decided to call this website “hierarchical brain” should therefore be obvious.
• The lower levels of my proposed structure describe how the brain processes data.
  • Using the basic capabilities of the low-level components of the brain (neurons and synapses), and given sufficient existing or potential synapse connections between the neurons, the brain has the ability to process data from any source using a standard method that is applied cumulatively and hierarchically.
    • This standard method has three elements: coincidence detection to spot synchronous events in incoming signals; lateral inhibition causing the strongest signals to have priority; and feedback connections to provide error correction, prediction capability and other important functions.
    • To save confusion with the use of terms such as “feedforward” and “feedback”, I prefer to use more precise technical terms: I describe incoming data signals as “afferent” and connections back towards the source as “efferent”.
  • The brain has no direct access to the outside world, but it analyses everything that it does have access to, which is actually the only thing it can do. This includes the processing of:
    • data from the external world via the well-known five senses (this processing is informally known as perception), but also from other lesser-known senses such as balance;
    • data from within the body relating to pain, the internal state of organs, and muscles and body position (technically called nociception, interoception and proprioception, respectively);
    • data about the processing of the brain itself (which I call “cognoception” because there doesn’t seem to be a term that describes it).
    All these signals are, in practical terms, indistinguishable - they are all identical electrical signals generated by neurons inside the brain; the only things that differentiate them are their source and their frequency.
  • Changes to the network over various timescales help to prioritise relevant signals and make correct predictions:
    • Changes to the strength and reliability of afferent (incoming) connections caused by coincidence detection create a memory of previous activity that helps to enhance future signals that are likely to be important.
    • Once these network paths are strengthened over many usages, they act as predictors of common incoming data structures.
    • Efferent connections (back in the opposite direction) are also strengthened by coincidence detection and with usage and so provide a means of correcting future errors and omissions and a further means of strengthening important incoming signals.
    • The strengths of connections can also be affected by more wide-ranging changes to the chemicals in the water that surrounds neurons in the brain. Hormones and other neuromodulators (such as alcohol) can cause temporary changes to the way connections are made, and this can then have longer lasting effects.
• The intermediate levels of my proposed structure describe the end results of the processing of data.
  • When the standard method of processing outlined above is considered from a higher-level viewpoint over many cumulative, hierarchical levels, the overall process can be described as compression, abstraction or generalisation, with prediction and selection. The essential or invariant features, or general characteristics, of the thing being sensed or analysed are extracted and remembered, and only the most important signals are processed up the hierarchy.
    • The structures created as a result of this cumulative process can be considered to be symbols that represent the things being sensed or analysed.
    • I call these structures “symbol schemas”, but other people have used different names for similar things.
    • A symbol schema that represents a thing is a large set of neurons and the synapse connections between them that are likely to all be activated at the same time when that thing is sensed.
    • A single neuron can participate in many symbol schemas and there is also a lot of duplication of pathways; in more technical terms, a symbol schema is degenerate, and also has resilience.
    • A symbol schema is simply a representation, it has no intrinsic meaning (but meaning arises with consciousness - see below).
    • Since data from the body and brain are also processed, a special symbol schema that I call the “self symbol schema” is also created.
    • Changes to the numbers, reliabilities and strengths of connections within and between symbol schemas is the primary way that the brain learns, and is the source of intelligence.
    • Symbol schemas are always linked to other symbol schemas that provide detail about relationships, and also more transient attributes such as absolute and relative positions in space and time and specific instance information.
    • Neuromodulation can affect the strengths of connections between symbol schemas, so affecting learning, thinking and levels of arousal, which includes sleep.
  • The efferent connections from a symbol schema back towards the source of the data are used for a number of things, the most important of which are:
    • To allow prediction in the case of incomplete or inconclusive incoming data, and to enhance important signals (the selection of the most important signals is the basis of what we call attention).
    • To keep a record of the sources (and later provide meaning) by connecting back towards sensory areas that were originally active when the thing being represented was sensed.
    • To specify the exact method of performing an action, and the order in which sub-actions must be performed.
  • When the collection of all symbol schemas and the connections between them are considered as a whole, the result can be described as a model of my world.
    • This model includes everything sensed in the outside world but also includes the body and the processing of the brain itself. It also includes non-real things such as future plans, creative thoughts, and fictional and impossible concepts.
    • The model is constantly being updated as new data is processed.
    • The term “schema” has sometimes been used for this whole model, or sometimes for part of the model, but I apply it to individual symbols.
  • The brain also processes data that originates from its own internal processes in exactly the same way as it processes all other incoming data.
    • I call this cognoception, and exact parallels can be drawn with perception.
    • For example, the processing compresses and simplifies the data, and the end result is a symbol schema that represents the original brain process.
    • However, because these symbol schemas reside within, and at the level of, my self symbol schema, they only contain information that is available at that hierarchical level, which equates to what is available to consciousness relating to the process of attention.
    • The symbol schema of my brain’s process for attention is particularly important in creating my self-awareness within the self symbol schema, but it is incomplete because it is totally unaware of the unconscious lower levels of processing that make up attention.
    • When a symbol schema representing a brain process is activated, it triggers that process, and this is a form of downward causation.
• The higher levels of my proposed structure show how the end results of the processing of data can provide the experience I have.
  • The way that all data is abstracted and compressed as described above to create symbol schemas and links between them shows that perception is based mainly on prediction and is therefore always influenced by past experience.
    • Perceptions are both not fully complete and not fully accurate, and therefore the model of my world that is created is also neither fully complete nor fully accurate; it consists of generalisations and idealisations.
    • An every-day example of this is when someone tells me something that I later relay to someone else, I don’t remember the exact words I heard, but I use different words that (hopefully) mean the same thing, or in some cases have a slightly different meaning.
    • No-one actually has a photographic visual memory, or the ability to remember sound like a digital recorder, although some people do have a better memory than others, but the brain has an amazing ability to compress and store huge amounts of information.
    • A perception can only have meaning if it connects to the self symbol schema and there are efferent connections back to the original source of the data. “Reinstatement” is the term I use for the reactivation of sensory neurons via efferent connections. Self-awareness is also needed (see below) for the meaning to be manifested.
    • A perception of an object, either in the outside world, within the body or within the brain, is not direct but is via the symbol schema for that object. I perceive only what I recognise, and I perceive via a symbol schema; this is proven by many sensory illusions.
  • My model of my body is not precise or complete, which is why I sometimes bang my elbow on a door. However, it is also flexible enough to allow me, after only a short time with a new size of tennis racquet, to be hitting a ball as if it were an extension of my own arm; it is also flexible enough to allow me to be fooled into thinking that a rubber hand is actually my hand.
  • Similarly, the symbol schemas of my own brain processing are generalised and idealised versions of the real thing, and only high-level, and I perceive my brain processes only indirectly, via those schemas.
  • To give a few examples, the self symbol schema is likely to specify, among other things, that:
    • I store and can recall fully everything I perceive;
    • the focus of my attention is fully under my conscious control and that I can block out any distractions;
    • my consciousness is either on or off - on when I am awake, and off when I am asleep or under anaesthetic;
    • I have full conscious control over my actions and take decisions based on rational, conscious thought - what is often called “free will”;
    • my brain creates “me” that is a constant presence, having a continuous existence from moment to moment - what is often referred to as “mind” or “soul”.
    The items in this list are things that people tend to assume (unconsciously) about their own brains as well as about other people’s brains, although these beliefs can obviously be altered by conscious knowledge. However, when these assumptions are examined or tested, it is easily found that in fact they are all almost completely false. These examples match very well with the end result that would be expected if a schema of the self including the brain were created in the way described above.
  • The logical conclusion is that the self symbol schema is more than just a model of me, it is me! Any feelings I have of self-awareness, qualia, consciousness etc., must be generated in this model, and it is the linking of this model to other symbol schemas and to sensory and motor areas of the brain that creates these feelings.
    • Not only are my perceptions of things in the outside world indirect, inaccurate and incomplete, but my perception of myself is also indirect, inaccurate and incomplete.
    • I become conscious of something only if the process of attention gives a signal sufficient priority that it connects to the self symbol schema.
    • If I sense something, but it does not become conscious, I can form no memory of it, it can have no meaning for me and I can have no feeling about it.
    • Feeling, meaning, qualia and emotions only come about because of relatively long-lasting connecting circuits between the relevant symbol schema and the self symbol schema.
    • Feelings and emotions have evolved as a useful feature to encourage the brain to promote survival of the genes, the self and the species (for example, pain, hunger, fear, curiosity, love, sexual desire etc.).
• Was Sherlock Holmes correct when he said “I am a brain” (the quote at the top of this page)? The concept of “I” has a hierarchy of at least three levels of meaning:
  1. “I” can be my brain and my body as a united and indivisible whole. In everyday speech, this is the most commonly understood meaning (“I” am throwing a frisbee).
  2. “I” can be said to be only my brain, as Arthur Conan Doyle has the cerebral Sherlock Holmes proclaim. On the face of it, this seems a reasonable statement because my brain is solely responsible for generating all my thoughts, desires, dreams and intelligence, and it controls all of my body and my behaviour, but when examined in more detail, there are some inconsistencies:
     • Without my body, my brain would not be able to create the “self” that is required for consciousness.
     • If “I” am my brain, why is it that “I” cannot control or even access a large number of important things that go on in my brain (normally referred to as unconscious processing)? For example, my blood pressure, my heart rate, my digestion system, my ability to walk and run, my processing of sense data, my process of attention, etc.
     • There are some important functions of my brain that I believe I have access to, but research has clearly proved that I am wrong about this. For example, I believe that I consciously control my attention, make decisions and take actions, but experiments have proven beyond doubt that large parts of these processes are done unconsciously and only reach my consciousness later.
     So “I am a brain” is understandable in the context of the Sherlock Holmes novel and the character who says it, but cannot be strictly true.
  3. My conclusion on this website is that “I” am only a small part of my brain, a model within my brain of me, my body and brain together. This model, my self symbol schema, has no access to the outside world, not even to most of the processing in the brain. It only has access to itself and other parts of the model of my world built by my brain when they connect to it. This explanation resolves the inconsistencies outlined above.
• This page is a summary of, and an introduction to, my proposals for how I think the human brain works. For further details, please see the links at the bottom of this page.
  • In the detail pages that are linked from the summary page, I have referenced many different scientific sources to justify most of my arguments.
  • Many of these sources provide or reference evidence that supports the arguments that I am proposing.
  • However, I have added some ideas of my own that may or may not be correct.
  • What I am proposing is essentially a possible model for the working of the brain.
  • I hope that my proposals provide food for thought and may lead to further research.

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Page last uploaded Sat Mar 9 12:29:17 2024 MST