Start With 100 Billion Brain Cells Called Neurons.
The brain is, by far, the most complex and mysterious organ in the human body. Composed of over 100 billion cells called neurons (sensory neuron and motor neurons also known as the brain’s ‘gray matter’ and the less known ‘white matter’ consisting of about another 100 billion glial cells that support the healthy functioning of neurons), this amazing structure is the center from which all of our skills of higher reasoning originate — creativity, learning, imagination, planning, and, perhaps most notable of all, our sense of identity. But how exactly does the physical brain make the transcendental leap to that much more esoteric concept, one’s sense of self? How does the brain work — and is it separate from what we might call the mind? These questions are still hotly debated in scientific, philosophic,religious, and cultural circles the world over,and the answers to them may well never be fully understood. Yet with the advent of modern neuroscience and psychology, much has come to be understood about the human brain.
A technical definition of the human brain begins, most simply, with the manner in which it is assembled. Each of its approximately 200 billion neurons connects to 10,000 others, forging a grand total of somewhere between 100-2000 trillion connections strung together by 90 million meters of neural fibers. Yet all of this neural density weighs between three to four pounds, and is set inside a cranium no more than 1 1/2 liters in volume, and the cortex (the brain’s rippled gray-matter surface, the center of all higher thought processes) is no greater in thickness and surface area than a formal dinner napkin.
If peeled apart, that cortical “dinner napkin” would reveal six distinct layers, each containing millions of interconnected neurons. Neurons on all layers communicate with each other through electrical impulses sent from the nucleus of each cell, down axons and across to dendrites of the surrounding neurons. This, in turn, allows the brain as a whole to communicate with the body it controls. Through neurons, the brain is able to receive information from numerous sensory receptors throughout the body, decide which of these sensory stimuli deserve attention, and send commands to initiate or inhibit various responses. Interestingly, the brain has far more capacity to respond to stimuli than it does to receive those stimuli in the first place; there are 10 times the number of feedback connections as there are “bottom-up” or sensory-input connections. It is, perhaps, this favoring of response over input that allows humans their remarkable skills at adapting to new, unfamiliar situations — their ability to interpret and innovate.
Parts Of The Brain:
From Brain Stem To Cerebellum and From Cortex To Frontal Lobe.
On a larger scale, the brain is made up of four distinct lobes on both the left and right hemispheres. The frontal, temporal, parietal, and occipital lobes each have primary processing functions, such as cognition, hearing, sensory input, and vision respectively, but they also serve act to regulate one another. The four major lobes have connections to the cerebellum in the base of the cranium to help regulate movement, and to the basal ganglia and midbrain, which relays signals between the brain, spinal cord, and body. The cerebellum can be seriously affected by alcohol abuse, which is why those who have too much to drink will end up stumbling home, unable to keep their balance! The nuclei in the basal ganglia are also critical for movement regulation, it is the connections between these nuclei that are the first to be affected in those with disorders like Parkinson’s (a loss of the ability to initiate movement) and Huntington’s (excessive uncontrollable movements) disease.
Seeing Brain Function With MRI & PET Scans
A Window Into Brain Activity.
The study of brain functions has been greatly augmented in recent years by the development of high-tech imaging techniques that allow scientists to observe the living brain in action. Blood flow imaging, functional magnetic resonance imaging, and electroencephalography all give scientists pictures of the activity taking place in a specific place of the brain while performing a specific activity. By understanding the electrical activity of the neurons making up a specific section of the brain, it is possible to develop a basic understanding of that section’s role in a given activity or in response to a given stimulus. The study of computational networks developed on supercomputers has also strengthened our theories about how the human brain forges and adapts its own neural networks.
These imaging and network technologies, along with a host of carefully controlled experiments and correlative studies, have informed us in large part of how learning and problem solving techniques are played out in the brain. We can describe with a good deal of confidence how the brain organizes its basic thinking tasks, such as planning and perception, and how the conscious brain applies both learned and intrinsic patterns of thinking to specific situations. And then, of course, all this is made possible by a well functioning human memory.
How Memories Are Made In The Brain
One area of particular interest, and of which our understanding is quickly growing, is that of human memory. Our memories are astounding in their capacity — for example, a young child learns about 10 new words each day, and the average adult can easily develop a vocabulary including over 100,000 words. It is the evolution of our memories that has, in large part, preserved our species. The key to our survival has been the ability of one generation to pass along its insights, innovations, and experiences to the next, so that they can improve upon them and progress more quickly forward.
Human memory can most broadly be defined as a function of the brain that gives us our ability to store and retrieve information. Science is fairly confident of the fact that there are many different types of memory, and many different mechanisms for their storage and retrieval processes. There are, potentially, as many types of memory as there are types of information and input to remember, and so the concept of one single brain section holding responsibility for memory has become somewhat obsolete.
In fact, there is general agreement upon the existence of sensory memories (taste, visual, tactile) as well as more conceptually based memories (episodic, procedural, declarative). All of these individual memory modes can combine to form much more complex and varied remembrances. Consider any significant childhood memory, perhaps the first time you can remember riding your bicycle without training wheels. During the moments in which that memory was created, your brain was processing thousands of pieces of information, and your memory had to decide which of those pieces were important enough to be worth storing for later retrieval. You might remember the emotions of fear and excitement; the tactile sensation of wind on your arms, or of the scrape on your knee if you fell; the sound of your mother’s encouraging words; procedural information (how to move your legs to push the pedals, the fine motor control of steering), and episodic information like the time of day, your age, and your general surroundings.
You probably do not remember less-central information such as the shoes you were wearing, or the colors of the cars parked along the curb where you rode; this information might have entered into your short-term memory, from which you might have been able to retrieve it for a few hours or even a couple of days. But only that information most central to the memory as a whole makes it into your long-term memory, where it lives for years —possibly an entire lifetime.
The multitude of information stored in long-term memory, and the wide variety of types of information stored, make it difficult to believe that any one brain structure could be solely responsible for that storage. Indeed, most theories point towards a long-term memory system that stores various types of remembered information in the brain areas most closely related to it —i.e., remembered words would be stored in the brainÕs language center, whereas a remembered sound would be placed on a mental “shelf” somewhere near the brain’s temporal lobes, primarily responsible for hearing. Then, the billions of interconnected neurons link these discrete pieces of a more complex memory together, so that, when retrieved, all of the information about that first bike ride comes to mind as a whole, rather than as a jumbled assortment of parts.
While the brain’s hippocampus (meaning “sea horse” because of the similarity in outwardly appearance) seems to be more directly related than any other structure to memory, it acts as a control center rather than a storage unit in and of itself. It, along with the entire cortex, and possibly white-matter cells throughout the nervous system called glial cell, are generally thought to be capable of holding memories.
How should science quantify a memory? What is the smallest piece of a memory, and where and how is it stored? The physical mechanisms making this intricate process possible are still being explored, and remain little-understood. Some theories suggest that protein particles are the building blocks for individual pieces of memories, although science has yet to explain how the relatively low durability of proteins can account for the sometimes lifelong persistence of a memory. Others point to brain cell networks and neuroplasticity, enabling chemical changes related to the emotional content of the ‘experience’ being remembered – in individual neurons grouped in particular networks – was accounting for memory. Also, synchronous neuron firing in larger networks will tend to have a bigger impact on the brain’s level of impression of the memory. This is probably related to other long-term, slowly-changing mental phenomenons like sense of identity and consciousness.
What Is Consciousness?
You Are What You Remember.
Consciousness itself is clearly quite a controversial and subjective topic. It is thought to involve both the modern neocortex found in all higher mammals (cats, dolphins, elephants, etc) as well as certain profoundly developed sections of the brain stem only found in humans. These “overdeveloped” sections, along with the extremely pronounced encephalization and connectivity of the human forebrain, may account for our superior communicative and innovative capabilities, as well as our unique ability to harness and control emotions. But can these traits be called consciousness?
Science has proven at least the existence, if not the clear definition, of consciousness. We know that people lose and regain it; that specific neuropathologies correspond with specific deficits in consciousness; and that conscious activities are impossible if key neural structures are lost. All of these ingredients indicate the presence of a direct link between the mind, human awareness, and the physical brain. Yet the subtleties of this link are still largely unknown, and questions regarding it may stump neuroscientists, psychologists, and philosophers for many years to come.
Recent brain studies investigating the electromagnetic theory of consciousness explores the possibility that the electromagnetic field generated by the brain is the actual carrier of conscious experience. The starting point for the theory is the fact that every time a neuron fires it also generates a disturbance to the surrounding electromagnetic (EM) field. Information coded in neuron firing patterns – occurring at the neuronal synapse – accounts for how information located in millions of neurons scattered throughout the brain can be unified into a single conscious experience:the information is unified in the EM field. When neurons fire together, their EM fields combine to generate stronger EM field disturbances; so synchronous neuron firing will tend to have a bigger impact on the brain’s EM field (and thereby consciousness) than the firing of individual neurons. Different EM field theories disagree as to the roleof the proposed conscious EM field on brain function.
Even with advanced techniques and technologies, we have yet to pinpoint the physical characteristics of the brain that build the most characteristic features of the human mind — creativity, intelligence, and self-awareness. The role played by genes, time, environment, and component parts from individual protein particles to neurons to the nervous system as a whole will continue to be explored. But that is not to say that we have not already built a large body of knowledge regarding the structure and function of the human brain; provided in this section are short descriptions of what we know today about the brain, nervous system, and some of its most important component parts.
Book Review
HOW THE HUMAN BRAIN DEVELOPS RIGHT FROM THE START
This topic is covered thoroughly in a book by Dr. Lise Eliot. PMI recommends this book. A credible review was written by Kritina Lerman and is reprinted here for your review.
What’s Going on in There: How the Brain Develops in the First Five Years of Life
This book belongs to a very distinguished class – a popular science book that is a real page turner. I literally could not put it down until I was too bleary eyed to stay awake. This is not so much a how-to-parent book, as a pop science book that explains how a baby’s brain develops from conception through the first few years of life. Of the several main claims to which the author returns again and again, the most important one is the critical role experience (and thus environment) plays in shaping the brain. Although I knew of the link before, I was surprised to learn just how important early experience is.
A baby is born with (almost) all of its neurons, but very few connections between them. The baby spends first few years (especially the first two) growing these connections, called synapses – many millions A SECOND – and also busily pruning them. Only those synapses that are stimulated by experience or practice will be preserved – the rest will be eliminated. All of our experiences, knowledge and understanding are encoded in the brain by a pattern of synapse strengths. The second point of the book is that the brain matures in phases, from the back of the brain, where the senses are perceived, to the front, where emotions and reasoning reside. Each part has a critical period of growth and myelination. The myelin sheath is the fatty substance around the neural connections that helps speed up signaling among neurons and between neurons and the rest of the body. If repeated experience is not provided during the critical period of some portion of the brain’s maturation, it will forever loose its functionality. Thus, for example, the auditory portion of the brain of deaf babies is not wired for hearing at all. Instead, it responds to visual stimuli. This is true not only of the senses (5 senses + vestibular system and motor skills) but also of language, emotion and reasoning skills.
The back-to-front maturation of the brain also explains why babies achieve their milestones in a certain progression – which was always a mystery to me. The chapters on emotion and language are especially fascinating, albeit too brief. For example, did you now that the baby first starts being able to feel emotions around 6 months? That’s when frontal lobes start maturing. This is synchronized with the motor development – baby begins to experience attachment and separation anxiety right around the time it begins to crawl (so as not to get too far from mommy)! It also explains why toddlers use nouns (telegraphic speech) first, and grammar much later, and why they are so (infuriatingly) slow – they should speed up as myelination of the brain progresses, through the first years of life.
The book offers a very coherent discussion of sex differences in the brain, physiological basis for temperament, and what can be done to override its negative aspects (such as an overly fearful child), genetic basis of intellect, etc. All ideas and arguments are convincingly presented, backed by experimental findings, not only on humans but on other species as well. The practical message was the one you already know and undoubtedly practice – stimulate your child – but the book explains well why this is necessary and why most parents instinctively know to do this. Still, there are a few things parents can do to give their child a developmental edge – talk, talk, talk to the child, practice attention and memory skills, talk, challenge the child to overcome negative emotional traits, talk some more.
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