by Gary L Wenk
How does my right brain talk to my left brain?
The two hemispheres of your brain talk to each other via the axonal highway made of axon fibers called the corpus callosum. Surprisingly, the size of the corpus callosum gets proportionally smaller as the cortex increases in size. Why? The reason is that decreasing the number of connections between hemispheres allows each half of your brain to spend less effort integrating its activity with the other half; this adaptation makes it possible for each half of your brain to specialize in specific abilities. For example, the part of the brain that controls the production of speech is solely in the left (usually) hemisphere. The advantage is that small regions of cortex in just one hemisphere can be dedicated to a particular function, thus allowing the same region in the other hemisphere to handle a different ability. This allows your brain to control a much broader range of abilities. The delegation of tasks to different hemispheres has many advantages.
There is also one very big disadvantage; small injuries in one hemisphere, due to a stroke or cancerous growth, can produce very big deficits in function. For example, a small stroke in just the left hemisphere might destroy your ability to talk. The distribution of specific abilities to a single hemisphere has made our species very broadly skilled and improved our chances of survival as an individual and species; the cost is that we are very vulnerable to small injuries.
Final thought
At the beginning of this book, I stated that my purpose was to provide the most accurate and up-to-date information possible about the brain. If I have achieved my goal, then you have gained some insights into how your brain is organized, how it evolved, and how it generates emotions, hallucinations, and memories. I hope that you also have learned that there is a degree of predictability in how your brain responds to drugs and the food you eat and that what you eat does influence how you think and how fast you age. I encourage you to continue learning more about your fascinating brain from the suggestions for further reading that are provided here. I promise that the more you learn about your brain, the more determined you will become to understand how your mind emerges from the three pounds of tissue floating in your head.
GLOSSARY
Acetylcholine A neurotransmitter in the brain and body that is formed by the combination of acetic acid and choline.
Acetylcholinesterase An enzyme present in nervous tissue and at the neuromuscular junction that catalyzes hydrolysis of acetylcholine to choline and acetic acid.
Action potential A brief change in the electrical charge across the membrane of a nerve that travels away from the cell body, along the axon, until it reaches the axon terminal, where it induces the release of a neurotransmitter.
Alzheimer’s disease An irreversible and progressive brain disorder that slowly impairs memory and thinking skills, and eventually the ability to perform simple tasks.
Amnesia An inability to remember past events or impairment in the ability to form new long-term memories.
Amygdala A structure located in the ventral region of the temporal lobe and considered to be a part of the limbic system. It is involved in the initiation of emotions, principally the production of a fear response.
Analgesic A drug that dulls the sensation of pain. It differs from an anesthetic agent in that it relieves pain without loss of consciousness.
Anticholinergic A drug that blocks, inhibits, or antagonizes the actions of acetylcholine or other cholinergic receptor agonists. Because the predominant effects of the parasympathetic nervous system are mediated by acetylcholine, the term “anticholinergic effects” often is used to imply an inhibitory action in the parasympathetic nervous system.
Anticonvulsant A drug that reduces the incidence of convulsions or seizures.
Anxiolytic A drug that reduces anxiety.
Astrocytes One of the three major classes of glial cells found in the central nervous system; important in providing nutrients to the neurons and removing metabolic and neurotransmitter byproducts.
Autonomic nervous system Subdivided principally into the sympathetic and parasympathetic efferent systems. It controls the function of visceral organs and allows the expression of the physical components of emotion.
Axon. The straight, relatively unbranched process of a nerve cell that carries the action potential to the terminal for release of a neurotransmitter.
B.C.E. Before the common era.
Bilateral On both sides of the brain.
Blood–brain barrier Functional barrier produced by glia wrapped around blood vessels preventing access for many blood-borne molecules to the brain. The barrier consists mostly of the fatty membranes of the astrocytes and the existence of tight junctions between the vascular endothelial cells.
Broca’s area An area in the left frontal lobe specialized for the production of speech.
Central nervous system The brain and spinal cord.
Cerebellum Means “little brain” in Latin. It is involved in learning, the coordination and production of speech, the organization of muscle movement, coordination of fine motor movement, and balance; it is the center of a feedback loop involving motor and sensory information.
Cerebral cortex The thin outer layer of the cerebral hemisphere, which contains neurons that are organized in six horizontal layers as vertical columns. It appears as ridges (gyri) and narrow folds (sulci) in order to maximize the number of neurons and number of columns within the confined space of the skull. It is responsible for all forms of conscious experience, including perception, emotion, thought, and planning. Cortex means “bark” in Greek; the bark of the cork tree looks a lot like the cerebral cortex.
Cerebral hemispheres The two halves of the brain. The left hemisphere is specialized for initiating speech, language, writing, and calculation. The right hemisphere is specialized for initiating spatial abilities, face recognition in vision, and some aspects of music perception and production.
Corpus callosum A large bundle of axon fibers that allows the two hemispheres of the brain to talk to each other. The two hemispheres use this axonal highway to coordinate the sensory processing and planning that takes place in both hemispheres.
Dementia Loss of higher intellectual function. This condition may be progressive due to some underlying disease process or may be drug induced.
Dendrite The parts of the neuron that receive information from other neurons. These structures contain receptors and are able to form synapses with incoming neurons.
Dura mater The thick external covering of the brain and spinal cord; one of the three components of the meninges, the other two being the pia mater and arachnoid.
Endocannabinoids The endogenous lipid-soluble chemicals anandamide and 2-AG that bind to the brain’s marijuana receptors. Endocannabinoids are unlike most of the brain’s transmitters because they are not stored in synaptic vesicles but are synthesized by neurons upon demand.
Endorphins Protein neurotransmitters that mimic the action of morphine.
Frontal lobe One of the four lobes of the brain; it includes all of the cortex that lies in the front half of the brain.
GABA Gamma-amino butyric acid is a neurotransmitter with major inhibitory function in the brain and body. Its primary function is to turn off the activity of other neurons.
Gastrointestinal system Pertaining to the stomach and intestines.
Glutamate A neurotransmitter with major excitatory function in the brain and body. Its primary function is to increase the activity of other neurons.
Gray matter The parts of the nervous system that contain neuronal cell bodies and very little myelin (known as white matter). In fresh dissection, these regions appear grayish.
Gyrus A ridge or fold between two clefts (sulcus) on the cerebral cortex. The gyri and sulci create the folded appearance of the brain in humans and other mammals.
Hallucination An altered sensory experience in a conscious and awake state that can be initiated by the brain or due to the presence of an external stimulus, such as a drug. Hallucinations are m
ost often visual and/or auditory, but also can involve the sense of taste, touch, and pain.
Hippocampus A structure found in the temporal lobe that is part of the limbic system and is important for the formation of new memories.
Ipsilateral On the same side of the body.
Hypothalamus A brain region located at the bottom center of the brain. It is responsible for controlling feeding behaviors, body temperature, thirst, and hormone release from the pituitary gland.
Limbic system A circuit of brain structures that plays a role in the control and production of emotional behavior.
Lipid solubility The property of a chemical to dissolve in fat. Due to the fatty components of the blood–brain barrier, lipid-soluble chemicals will enter the brain more easily than chemicals that are not lipid soluble.
Long-term potentiation (LTP) An increase in size of a synaptic electrical potential lasting one hour or more. LTP is considered an artificially produced electrophysiological representation of the actual neural processes that underlie a memory.
Mammal An animal the embryos of which develop in a uterus and the young of which begin to suckle at birth (technically, a member of the class Mammalia).
Microglial A type of glia that plays a critical role in the immune responses of the brain.
Mitochondria A small membrane-bound organelle found in large numbers in most cells of the body, in which the biochemical processes of respiration and energy production occur.
Myelin A sheath of fatty material that surrounds most axons. It acts as an insulator to enhance electrical conduction of action potentials.
Myelination Process by which glial cells wrap axons to form myelin that increase axonal conduction velocity.
Narcolepsy A rare disabling hypersomnia disorder that may include cataplexy, sleep paralysis, hypnagogic hallucinations, and sleep-onset rapid eye movement (REM) periods, but also disrupted nighttime sleep by nocturnal awakenings, and REM sleep behavior disorder (RBD).
Neuron The basic functional unit of the nervous system, also called a nerve cell. It is specialized for the transmission of information and characterized by long fibrous projections called axons, as well as shorter, branch-like projections called dendrites.
Neurotransmitter A chemical substance produced within neurons from components of the diet and released by neurons to diffuse into the extracellular environment and bind to specific postsynaptic protein receptors on a neighboring neuron.
Non-rapid eye movement (non-REM) sleep Collectively, those phases of sleep characterized by the absence of rapid eye movements.
Nystagmus An involuntary, usually lateral, back-and-forth rhythmic eye movement.
Occipital lobe One of the four lobes of the brain. It is responsible for vision and visual object and face recognition. This lobe is located at the most posterior part of the brain.
Orexin A protein neurotransmitter that controls arousal and feeding behaviors.
Parasympathetic nervous system Part of the autonomic nervous system. This system is involved with maintenance of bodily activities and conservation of energy.
Parietal lobe One of the four lobes of the brain. It is responsible for processing higher sensory and language functions. This lobe is located on the top of the brain.
Parkinson’s disease A degenerative disease that results in a tremor at rest, usually involving the hands and feet at first, along with a general slowness in movement.
Pia mater The innermost layer of the membranes surrounding and protecting the brain that closely follows the bumps and wrinkles of the brain’s surface.
Placebo A medicine or preparation with no pharmacologic activity, which is effective only by virtue of the power of suggestion associated with its administration.
Poikilotherm An organism whose internal temperature varies in relation to the temperature of the environment. It is the opposite of a homoeotherm, an organism that maintains thermal homeostasis.
Prefrontal cortex The very anterior-most part of the brain, which controls planning and thought.
Presynaptic The site from which the neurotransmitter is released, usually at the end of an axon.
Pseudoscience A claim, belief, or practice that is incorrectly presented as scientific but does not adhere to a valid scientific method, cannot be reliably tested, or otherwise lacks scientific status.
REM atonia A sleep disorder characterized by the loss of normal voluntary muscle tone during REM dream sleep.
REM behavior disorder Dream-enacting behaviors and movements during REM sleep. RBD is commonly associated with Parkinsonism and narcolepsy.
Receptor A protein floating on the surface of a neuron. Usually these proteins are the point of interaction between two neurons or between a drug and a neuron.
Reuptake When some neurotransmitters are released into the synaptic cleft, a fraction of the released molecules is recovered by transport back into the axon terminal, where it may be reused or degraded. Some drugs (called selective reuptake inhibitors) can interfere with this process.
Serotonin A neurotransmitter derived from the dietary amino acid tryptophan.
Sulcus (plural = sulci) The valleys or spaces between the folds or gyri of the brain.
Sympathetic nervous system The sympathetic nervous system is part of the autonomic nervous system. In general, this is a system that is involved with activation of bodily activities and mobilization of energy-consuming activities (increase in heart rate, respiration). This system has been characterized as the “flight-or-fight” system.
Synapse The place where one neuron connects to another neuron. The synapse includes the nerve terminal of the first neuron, the spot on the second neuron with receptors, and the space between them.
Synaptic vesicles Membrane spheres that contain neurotransmitter molecules that are stored near the presynaptic membrane at the synapse.
Synesthesia A phenomenon in which stimulation of one sensory pathway leads to automatic, involuntary experiences in a second sensory pathway. The experience varies in intensity and people vary in awareness of their synesthetic perceptions.
Temporal lobe One of the four lobes of the brain. It is responsible for processing hearing, olfaction, object recognition, language, speech, learning, and memory. It is located on lateral sides of each brain hemisphere near the ears.
Wernicke’s area Region of cortex in the left temporal lobe that helps mediate language comprehension.
White matter Those parts of the brain and nervous system that primarily contain axons wrapped with myelin.
FURTHER READING
Chapter 1
Bliss TV, Collingridge GL (1993) A synaptic model of memory: long-term potentiation in the hippocampus. Nature, Vol 361, pp. 31–39.
De Leon J, Diaz FJ (2005) A meta-analysis of worldwide studies demonstrates an association between schizophrenia and tobacco smoking behaviors. Schizophrenia Research, Vol 76, p. 135.
Eichenbaum H (2008) Learning and Memory. New York: W. W. Norton & Company.
Giocomo LM, Hasselmo ME (2007) Neuromodulation by glutamate and acetylcholine can change circuit dynamics by regulating the relative influence of afferent input and excitatory feedback. Molecular Neurobiology, Vol 36, p. 184.
Gluck MA, Mercado E (2013) Learning and Memory: From Brain to Behavior, 2nd ed. Duffield, UK: Worth Publishers.
Hamann S (2005) Sex differences in the responses of the human amygdala. The Neuroscientist, Vol 11, p. 288.
Pfeiffer BE, Fostser DJ (2015) Autoassociative dynamics in the generation of sequences of hippocampal place cells. Science, Vol 349, p. 180.
Wenk GL (2003) Functional neuroanatomy of learning and memory. In: DS Charney, EJ Nestler, & BS Bunney (Eds.), Neurobiology of Mental Illness, 2nd ed., pp. 807–812. New York: Oxford University Press.
Wenk GL (2006) Neuropathologic changes in Alzheimer’s disease: Potential targets for treatment. Journal of Clinical Psychiatry, Vol 67, p. 3.
Wenk GL (2014) Your Brain on Food: How Chemicals Control Your Thoughts and Feelings,
2nd ed. Oxford: Oxford University Press.
Chapter 2
Dravets WC, Price JL, Bardgett ME, Reich T, Todd RD, Raichle ME (2002) Glucose metabolism in the amygdala in depression: Relationship to diagnostic subtype and plasma cortisol levels. Pharmacology Biochemistry and Behavior, Vol 71, p. 431.
Falkai P, Rossner MJ, Schulze TG, Hasan A, Brzozka MM, Malchow B, Honer, et al.,(2015) Kraepelin revisited: schizophrenia from degeneration to failed regeneration. Molecular Psychiatry, Vol 20, p. 671.
Gazzaniga MS (2015) Tales from Both Sides of the Brain: A Life in Neuroscience. New York: Harper Collins.
Jamison KR (1996) An Unquiet Mind: A Memoir of Moods and Madness. New York: Vintagem.
Kramer P, Bressan P (2015) Humans as superorganisms: how microbes, viruses, imprinted genes, and other selfish entities shape our behavior. Perspectives on Psychological Science, Vol 10, p. 464.
Ladoux J (1998) The Emotional Brain: The Mysterious Underpinnings of Emotional Life. New York: Simon & Schuster.
Loftus EF (1979) The malleability of human memory. American Scientist, Vol 67, p. 312.
Lohoff FW (2010) Overview of the genetics of major depressive disorder. Current Psychiatry Report, Vol 12, p. 539.
Molgat CV, Pattan SB (2005) Comorbidity of major depression and migraine: A Canadian population-based study. Canadian Journal of Psychiatry, Vol 50, p. 832.