The human brain is amazing, weighing just about 3 pounds [1’4 kilograms] it is the most complex part of the human system and one of the most complex objects in the known Universe.. A big thing about the brain is its connectivity abilities, its essentially a network of over 100 billion [wow!] individual nerve cells interconnected in systems that join up and construct our reality. Recent advances in brain imaging techniques is revealing lots about our brains neural circuits, we can confidently point to regions of the brain associated with particular modes of thinking and feeling. Our brains constantly manage multiple streams of information from our internal and external environments to ensure we get the physical, social and emotional nourishment [as directed by our innate templates] needed for us to survive, maintain ourselves and grow. Our creative thoughts, feelings, and plans are developed by the our brains complex systems of connectivity. It processes our feelings and thoughts, stores and retrieves our memories, fixes our attention and controls the drivers of our behaviours. It took millions of years for our human brains to evolve to the point where we have the knowledge to direct our own development. Yet, not all our perceptions are conscious ones, a lot of our behaviour is influenced by unconscious processes including many motivations that make us behave in certain ways. The information in this article combined with other articles on this site, provide insights into the mental processes involved in human perception. learning, memory and behaviours – the essence of you!
A cautionary note, although this article specifically focuses on the brain, it is important to understand that the brain/body system is the more holistic view of human functioning which exerts its own individual influences on our lives, such as our experiences of pain and pleasure and our success, or not, at social connections. Empirical evidence about the minds influence on our physical and mental health and disease processes is widely available. Research into the brain-body systems [sometimes referred to as the embodied mind] is gaining momentum and is likely to improve our understanding about the nature of consciousness and our perceptions of self in space and time [big stuff]. We will provide information elsewhere on this site about specific brain body effects that are supported with empirical and scientific explanations.
The brains neuroplasticity – Movement, language, perception, thought, memory, are all made possible by the serial and parallel interlinking of several brain regions each with their specific functions. We know that damage [such as what happens in brain trauma through strokes or accidents] to a single area of the brain does not always result in the complete loss of an entire faculty. Even if a behaviour initially disappears, there may be a a complete or partial return as undamaged areas of the brain reorganise their linkages – this is known as the brains neuroplasticity. This is an important concept in understanding the brains potential for retuning itself to meet your needs.
There are a number of ways to describe the architecture of the brain in terms of its form and functions, in this article we will consider its different regions, its most basic units of function and the current thinking about how the human brain has evolved and link this to how we behave. A common approach is to classify the brain anatomically based on the embryonic development of 3 regions: the forebrain, midbrain and hindbrain. All these regions work together as one brain, but each part also has its specialist properties.
Brain Cells – Before exploring the different regions of the brain, it is important to understand the cells and tissues that are the building blocks of them all. Brain cells are different from other cells of the body. There are two main types : neurons and glial cells. Although the brain has many other types of cells, these are the ones most involved in learning. A neuron has three basic parts: the cell body, the dendrites, and the axon. Information enters the cell body through dendrites, which are really constantly moving appendages seeking information. If the neuron needs to send a message to another neuron, the message is sent through the axon. There is no direct physical contact between communicating neurons. The message has to go from the axon of the sending neuron to the dendrite of the receiving neuron by “swimming” through a space called the synapse. When the signal reaches the end of the axon it stimulates the release of tiny sacs called vesicles that release chemicals known as neurotransmitters into the synapse. Neurotransmitters are chemical messengers which relay, amplify and modulate signals between neurons and other cells. The two most common neurotransmitters in the brain are the amino acids glutamate and GABA. Other important neurotransmitters include acetylcholine, dopamine, adrenaline, histamine, serotonin and melatonin. The electro-chemical signal released by a particular neurotransmitter may encourage the receiving cell to fire, or inhibit or prevent it from firing. Excitatory neurotransmitters include: acetylcholine, glutamate, aspartate, noradrenaline and histamine. Inhibitory neurotransmitters include GABA, glycine and serotonin while dopamine may be either. The neurotransmitters cross the synapse and attach to receptors on the neighbouring cell. These receptors can change the properties of the receiving cell, they cause changes in the permeability of the cell membrane to specific ions, opening up special channels which let in a flood of charged particles (ions of calcium, sodium, potassium and chloride). This affects the potential charge of the receiving neuron, starting up a new electrical signal in the receiving neuron. The whole process takes less than one five-hundredth of a second [another WOW!]. The interactions of neurons is both electrical and electro-chemical, a message within the brain is converted, as it moves from one neuron to another, from an electrical signal to a chemical signal and back again. It is possible for each individual neuron to form thousands of links with other neurons – a typical brain has up to 1000 trillion synapses. Functionally related neurons connect to each other to form neural networks. The connections between neurons are not static and change over time. The more signals sent between two neurons, the stronger the connection grows (the amplitude of the post-synaptic neuron’s response increases), and so, with each new experience and each remembered event or fact, the brain slightly re-wires its physical structure. As the neurons make connections, the brain is growing dendrites and strengthening the synapses. The phrase “neurons that fire together wire together” is often used to explain this phenomenon.
The second type of brain cell, the glial cell are nurturing cells for the neurons. . Glial cells first assist in the migration of neurons during fetal brain development. Their fibers act like ropes for the neurons to hold onto as they make their way through the brain (Kunzig, 1998). The glial cells feed and do the housekeeping for the neurons, almost attaching themselves to the neurons to keep them nourished. The more often the brain uses neurons, the more glial cells it needs and the more the brain produces them. Communication remains fast and easy because our glial cells work and nurture the neurons.
The biggest, and most uniquely human part of the brain is the forebrain, which contains a number of important structures and sub regions including the cerebrum., the limbic system. and the hypothalamus.
In our human brains the cerebrum is king. Here lies our control centre for higher level brain functions such as logic, reasoning, language and creativity. The outer surface of the cerebrum is about 3 millimetres thick and a great design feature is its highly folded layer of grey matter known as the cerebral cortex. The cerebral cortex is our electrical power station consisting of closely packed neurons that control most of our body functions, including the not yet fully understood state of consciousness, our senses, the body’s motor skills, reasoning and language. The convoluted folds of the cerebral cortex is natures way of fitting a large cortical surface area into the confines of our skulls. Unfolded the cerebral cortex would extend to measure over 2 square metres. The bulges of cortex are called gyri (singular: gyrus) while the indentations are called sulci (singular: sulcus). The cerebral cortex is the processing unit of the cerebrum, it controls perceptions and other higher level cognitive functions such as our ability to reason, to concentrate and to think in abstract forms. A deep furrow known as the longitudinal fissure runs down the centre of the cerebrum, dividing it into the left and right hemispheres. A band of white matter called the corpus callosum connects the left and right hemispheres of the cerebrum and allows the hemispheres to communicate with each other. Each hemisphere is further divided into 4 lobes: frontal, parietal, temporal, and occipital named in relation to the skull bones that cover them. The specialisations and connections associated with these 4 lobes could be considered in some part to represent the architectural structures of our thoughts and feelings. The cerebrum is positioned over and around most other brain structures, and its four lobes with their specialised functions are intensively connected.
- The occipital lobes at the back of the brain contain the primary visual cortex, this is where images from the eyes are processed and linked to information with images stored in memory.
- The parietal lobes sit behind the frontal lobes. The forward parts of these lobes, behind the motor areas, are the primary sensory areas receiving information about temperature, taste, touch, and movement from the body. When you enjoy a good meal, the parietal lobe is at work. The parietal lobes process complex information and are involved in sensing body position, spatial awareness and integrating visual information. You put your parietal lobes to work when trying to judge if you have time to cross the road safely before the car you can see in the distance reaches you. Factual messages, detailed communication, reading and arithmetic are also functions in the repertoire of each parietal lobe.
- The temporal lobes lie in front of the visual areas and nest under the parietal and frontal lobes. They major in processing auditory signals but they have some involvement across all our five senses. Top of each temporal lobe is an area responsible for receiving information from the ears. The left temporal lobe also contains Wernicke’s area, a part of the brain involved in language comprehension. The underside of each temporal lobe plays a crucial role in forming and retrieving memories, including those associated with music. Other parts seem to be involved in integrating memories and sensations of taste, sound, sight, and touch.
- The frontal lobes are the most recently evolved part of our human brain. They process memory, allow us to set goals. imagine the future, be creative, make rational decisions and exercise social judgment. The prefrontal cortex, is the brain’s top executive function. It is here that we organise our responses to complex problems, plan things, search our memories for relevant experience, and adapt strategies in light of new information. This area also executes influence that helps us manage emotional impulses in socially appropriate ways, it is essential in helping us behave in ways best suited to getting our needs met. It supports empathy, altruism and interpretation of facial expressions. This area works things out and effectively edits information before being processed by the hippocampus. The frontal lobes also contain the primary motor cortex, which controls muscle movement. Broca’s area, – which influences speech production by allowing us to turn thoughts into words, is located in the left frontal lobe.
The limbic system [our emotional brain] is another deep grey matter region of the forebrain, containing the amygdala and hippocampus which are involved in memory, survival, and emotions. If the cerebrum is King of our thinking and cognitive abilities then our limbic system can be thought of as Queen Bee of our emotional intelligence. The limbic system triggers the bodies response to emergency and highly emotional situations with fast, almost involuntary actions. Parts of the limbic system also lie in the thalamus and the hypothalamus.
- The amygdala [strictly speaking you actually have two amygdalae] is seated in the temporal lobes behind our ears and deep in the centre of the limbic emotional brain. This powerful little brain structure packs a lot of clout over our mental and physical well being. In fact, the amygdala seems to modulate all of our reactions to events it deems important for our survival- not just events that warn us of imminent danger but also signals about the presence of food, sexual partners, rivals, children in distress, and so on. Often described as being the size and shape of an almond [although this is a bit misleading because the its structure is now known to be bigger], in evolutionary terms this part of the brain has been around a while. Designed to be the bodies alarm centre, its neural circuits are cleverly grouped together. Consequently, many sensory inputs converge in the amygdala to inform it of potential dangers in the environment. Sensory information reaches the amygdala either directly from the thalamus of from various sensory cortexes. Several other regions of the brain project their axons to the amygdala; including the hypothalamus, the septum and the reticular formation of the brainstem. Essentially the amygdala works to decode emotions such as fear, anger, and pleasure. It is highly sensitive to stimuli that we perceive, rightly or wrongly, as threatening to our ability to get our survival needs met. By default it is an unconscious processor, it can learn and store memories on its own [outside the conscious control of our frontal cortex] to control our emotional responses. This is an important concept to understand – the amygdala processes signals coming into the brain from our environment, before our thinking brain in the cortex, this gives it enormous potential to hijack our ability to think straight. When the thalamus gathers up information [sight, sound etc.] it routes it through the amygdala and the cortex, but it arrives in the amygdala slightly ahead of the cortex [about half a second earlier]. On receiving the signals the amygdala compares the information to stored emotional memories [these memories will be connected to our emotional needs] and a rudimentary pattern match is formed. If the amygdala perceives the stimulus as threatening, it will initiate a survival fight or flight response without checking anything out with the left cortex. It then forces the cortex into black and white, either or, type thinking and triggers the autonomic components of emotional arousal through activation of the nerves of the sympathetic division. It can speed up the heart rate, dilate the pupils, increase the metabolic rate, and increase the blood flow to our muscles, primarily through output pathways to the hypothalamus and brain stem. It is the actions of the amygdala that make us succumb to anger, panic attacks, anxiety etc. The term ‘losing it’ seems very apt when considering the power of the amygdala to hijack and close down access to our thinking brain in the frontal cortex. This determination happens partly as a result of a persons subjective experience [linked to memories] to the strength of the emotional response an event invokes. Although connections from the prefrontal cortex to the amygdala enable us to exercise a certain conscious control over any anxiety, this ability can also create anxiety by allowing us to imagine failure, disaster or the presence of dangers that do not actually exist. Fear conditioning happens in the amygdala, it is an associative learning process by which we learn through repeated experiences, to fear something. Our experiences can cause brain circuits to change and form new memories. For example, when we see something unpleasant, the amygdala heightens our perception of the visual stimulus. This heightened perception is deemed distressing [pattern matching to an emotional memory coded with the feeling of distress] and emotional memories are formed associating the visual scene with unpleasantness. The amygdala also receives numerous connections from the hippocampus, because the hippocampus is involved with storing and retrieving explicit memories, this may explain the origin of strong emotions that get triggered by particular memories. The central nucleus of the amygdala also produces conscious perception of emotion primarily through output pathways to the anterior cingulate cortex, orbitofrontal cortex, and prefrontal cortex. A range of conditions such as anxiety, autism, depression, post-traumatic stress disorder, and phobias are all linked to the functioning of the amygdala.
- The hippocampus is a small organ located within the brain’s temporal lobe and is often described as the brain’s hard drive, where long-term memory lives. We actually have 2 hippocampi, situated on the left and right sides of the cortex. Once experiences and learning have been processed by the hippocampus, they can be there permanently. An arching tract of nerve cells leads from the hypothalamus and the thalamus to the hippocampus. This tiny nub acts as a memory librarian—sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary. Feelings that we perceive are decoded in various sensory areas of our cortex, and regrouped to gather in our hippocampus as a single experience. The hippocampus analyses inputs and seems to be responsible for deciding if they will be committed to long-term memory. It compares and associates new inputs with previously recorded ones and sorts the information into codes that are then stored in various different parts of the our brains. The exact way in which these pieces are identified and recalled later remains an active area of research. The role of the hippocampus in memory has in part been informed by case studies of unfortunate individuals who have suffered damage to this area of their brain, or in some cases had it removed rendering them incapable of creating new memories – a condition known as Anterograde Amnesia. The hippocampus is one of the few areas of the brain where new neurons actually grow.The hippocampus also plays an important role in spatial navigation and and our abilities to construct cognitive maps. Studies of London Cab drivers show they have hippocampi larger than the general population. A form of neural plasticity known as long-term potentiation (LTP) was first discovered to occur in the hippocampus. LTP, it is believed to be the main neural mechanism by which memory is stored in the brain. The hippocampus is implicated in the pathology of schizophrenia and is one of the first functions to falter in people with Alzheimers.
- The thalamus located at the top of the brain stem is a major clearing house for information going to and from the spinal cord and the cerebrum . All sensory information except smell-related data, transcends through the thalamus on the way to the cerebrum. Sensory neurones entering the brain from the peripheral nervous system form relays with neurones in the thalamus that continue on to the cerebral cortex. The thalamus plays a role in controlling the motor systems of the brain which are responsible for voluntary bodily movement and coordination. It is also involved in the regulation of consciousness and sleep. Thalamic nuclei are part of the thalamo-cortico-thalamic circuits that effect arousal, wakefulness and alertness. Damage to the thalamus is associated with risk of coma and conversely a portion of the thalamus, called the pulvinar, helps in refocusing our attention. The thalamus receives input from the retina which is relayed to the brain via the optic nerve and then forwarded to the primary visual cortex in the occipital lobe . Additionally the thalamus also influences learning by routing sensory information into processing and memory centres of the cerebrum.
- The hypothalamus is about the size of a pearl and lies under the thalamus at the base of the brain where signals from the brain and the body’s hormonal system interact. It maintains the body’s homeostasis and links the nervous system to the endocrine system. The hypothalamus processes the sensory information that it receives and sends the output to autonomic effectors in the body such as sweat glands, the heart, and the kidneys. It controls body temperature, hunger, thirst, fatigue, and circadian cycles. Despite its relatively small size, the hypothalamus comes packed with nuclei with vital functions. It exerts its influence across many of our different motivations associated with getting our needs met. It works to control major behaviours such as eating, drinking and sexual behaviour. By controlling the molecules associated with making us happy, sad, exhilarated, unhappy or angry, it plays its part in controlling our strong emotional behaviours such as rage, fear, pain and pleasure. The hypothalamus exerts a lot of its influence by producing hormones that control the pituitary gland. Some of these hormones, such as oxytocin and antidiuretic hormone, are stored in the posterior pituitary gland. Other hormones, such as releasing and inhibiting hormones, are secreted into the blood to stimulate or inhibit hormone production in the anterior pituitary gland. It is the hypothalamus that wakes you up in the morning, and gets the adrenaline flowing.
- The pineal gland produces the hormone melatonin. Light striking the retina of the eyes sends signals to inhibit the function of the pineal gland. In the dark, the pineal gland secretes melatonin, which has a sedative effect on the brain and helps to induce sleep. This function of the pineal gland helps to explain why darkness is sleep-inducing and light tends to disturb sleep. Babies produce large amounts of melatonin, allowing them to sleep as long as 16 hours per day. The pineal gland produces less melatonin as people age, it can be implicated with difficulty in sleeping during adulthood.
The Midbrain is the region of the brain lying between the hindbrain and the forebrain. It helps us to locate events in space and is involved in the control of some reflex actions. It forms part of the circuit involved in the control of eye movements and other voluntary movements. It also contains a system of neurones that releases the neurotransmitter dopamine. The reticular formation runs through the hindbrain and the midbrain and is involved in sleep and wakefulness, pain perception, breathing, and muscle reflexes.
The Hindbrain is composed of the medulla, the pons, and a wrinkled ball of tissue called the cerebellum. The medulla lies next to the spinal cord and controls essential functions outside conscious control, such as breathing and blood flow. The pons affects activities such as sleeping, waking, and dreaming. The cerebellum – 2 peach-size mounds of folded tissue located at the top of the brain stem, is the guru of skilled, coordinated movement (e.g., skateboarding or threading a needle). Anyone who has great hand eye coordination can thank their cerebellum.
Article by Ingrid Blades December 2014