3.2: Our brain controls our thoughts, feelings and behavior (2023)

learning objectives

1. Describe the structure and function of the "old brain" and its influence on behavior.
2. Explain the structure of the cerebral cortex (its hemispheres and lobes) and the function of each area of ​​the cortex.
3. Define the terms brain plasticity, neurogenesis, and brain lateralization.

The Old Brain: Primed for Survival

The brainstem isthe oldest and innermost region of the brain. It is designed to control life's most basic functions, including breathing, attention, and motor responses (Figure \(\PageIndex{8}\)). The brainstem begins where the spinal cord enters the skull and forms the medulla,the area of ​​the brainstem that controls heart rate and breathing. In many cases, the spinal cord alone is enough to sustain life – animals that have the rest of their brains above the severed spinal cord are still able to eat, breathe and even move. The spherical shape above the medulla is the bridge,a structure in the brainstem that helps control body movements and plays a particularly important role in balance and walking.

A long, narrow network of neurons traverses the medulla and ponsknown as the reticular formation. The job of the reticular formation is to filter some of the stimuli that enter the brain from the spinal cord and relay the rest of the signals to other areas of the brain. The reticular formation also plays important roles in walking, eating, sexual activity, and sleep. When electrical stimulation is applied to an animal's reticular formation, it immediately becomes fully awake, and when the reticular formation is severed from the higher regions of the brain, the animal falls into a deep coma.

Above the brainstem are other parts of the ancient brain that are also involved in processing behavior and emotions (Figure \(\PageIndex{9}\)). WhatthalamusIt isthe egg-shaped structure above the brainstem that applies even more filtering to sensory information coming from the spinal cord and through the reticular formation, and relays some of these residual signals to higher levels of the brain(Guillery & Sherman, 2002). The thalamus also receives some of the higher brain responses and relays them to the medulla and cerebellum. The thalamus is also important during sleep because it shuts off signals received from the senses so that we can rest.

Little brain (literally "little brain")it consists of two crinkled ovals behind the brainstem. Functions to coordinate voluntary movement. People with damage to the cerebellum have trouble walking, keeping their balance, and keeping their hands steady. Alcohol consumption affects the cerebellum, which is why drunk people find it more difficult to walk in a straight line. The cerebellum also contributes to emotional responses, helps us distinguish between different sounds and textures, and is important in learning (Bower & Parsons, 2003).

Although the primary function of the brainstem is to regulate the most basic aspects of life, including motor functions,limbic systemit is largely responsible for memory and emotion, including our responses to rewards and punishments. The limbic system isan area of ​​the brain, located between the brainstem and the two hemispheres of the brain, that controls emotions and memory.Includes the amygdala, hypothalamus and hippocampus.

the amygdalato spendof two "almond-shaped" clusters (amygdala comes from the Latin word for "almond") and is primarily responsible for regulating our perception and responses to aggression and fear. The amygdala has connections to other fear-related bodily systems, including the sympathetic nervous system (which we'll see later is important in fear responses), facial responses (which perceive and express emotions), processing odors, and releasing stress-related neurotransmitters. and aggression (Best, 2009). In an early study, Klüver and Bucy (1939) damaged the amygdala of an aggressive rhesus monkey. They found that the once angry animal immediately became passive and no longer responded to fearful situations with aggressive behavior. Electrical stimulation of the amygdala in other animals also affects aggression. In addition to helping us experience fear, the amygdala also helps us learn from fearful situations. When we experience dangerous events, the amygdala stimulates the brain to remember the details of the situation so that we learn to avoid it in the future (Sigurdsson, Doyère, Cain, & LeDoux, 2007).

Located just below the thalamus (hence its name) is the hypothalamus.a brain structure that contains a series of small areas that perform a variety of functions, including the important role of connecting the nervous system to the endocrine system via the pituitary gland. Through its many interactions with other parts of the brain, the hypothalamus helps regulate body temperature, hunger, thirst, and sex, and responds to satisfying these needs by creating feelings of pleasure. Olds and Milner (1954) discovered these reward centers by accident after momentarily stimulating the hypothalamus of a rat. The researchers observed that after being stimulated, the rat continued to move to the exact spot in its cage where the stimulation took place, as if trying to recreate the circumstances around its original experience. After further research on these reward centers, Olds (1958) found that animals would do almost anything to recreate a pleasurable stimulation, including crossing a painful electrified grid to receive it. In one experiment, a rat was given the opportunity to electrically stimulate its own hypothalamus by pressing a pedal. The rat enjoyed the experience so much that he pressed the pedal over 7,000 times an hour until he passed out from exhaustion.

Hippocampusto spendof two "horns" arched behind the amygdala. The hippocampus is important for storing information in long-term memory. If the hippocampus is damaged, a person cannot form new memories, but instead lives in a strange world where everything they experience simply disappears, even while memories from before the damage are intact.

The cerebral cortex creates consciousness and thought

All animals have adapted to their environment by developing skills that help them survive. Some animals have hard shells, others run extremely fast, and some have acute hearing. Humans don't have any of these special qualities, but we have one big advantage over other animals - we're very, very smart.

You might think that we should be able to determine an animal's intelligence by looking at the ratio of the weight of the animal's brain to the weight of its entire body. But that doesn't really work. An elephant's brain weighs one-thousandth of its weight, but a whale's brain is only one-tenth of a thousandth its body weight. On the other hand, although the human brain is one-sixtieth of its body weight, the mouse brain is one-fortieth of its body weight. Despite these comparisons, elephants don't look 10 times smarter than whales, and humans certainly look smarter than mice.

The key to humans' advanced intelligence does not lie in the size of our brains. What separates humans from other animals is our large cerebral cortex—the cortex-like outer layer of our brain that allows us to use language successfully, acquire complex skills, create tools, and live in social groups(Gibson, 2002). In humans, the cerebral cortex is wrinkled and folded rather than smooth as in most other animals. This creates a much larger surface area and size and allows for greater ability to learn, remember and think. Folding of the cerebral cortex is referred to ascorticalization.

Although the cortex is only about a tenth of an inch thick, it accounts for over 80% of the brain's weight. The cortex contains about 20 billion neurons and 300 trillion synaptic connections (de Courten-Myers, 1999). Supporting all these neurons are billions of glial cells (glia),cells that surround and connect to neurons, protect them, provide nutrients, and absorb unused neurotransmitters. Glia come in different forms and have different functions. For example, the myelin sheath that surrounds the axon of many neurons is a type of glial cell. Glial cells are essential partners of neurons, without which neurons could not survive or function (Miller, 2005).

The cerebral cortex is divided into twohemispheres, and each hemisphere is divided into fourpatches, each separated by folds known ascracks. If we look at the cortex, starting at the front of the brain and moving along the top (Figure \(\PageIndex{10}\)), we see the frontal lobe first (behind the forehead),which is primarily responsible for thinking, planning, memory, and judgment. After the frontal lobe is the parietal lobe,which extends from the center to the back of the skull and is primarily responsible for processing touch information. Then comes the occipital lobe,at the back of the skull, which processes visual information. Finally, in front of the occipital lobe (approximately between the ears) is the temporal lobe,primarily responsible for hearing and language.

Functions of the cortex

When German physicists Gustav Fritsch and Eduard Hitzig (1870/2009) applied mild electrical stimulation to different parts of a dog's cortex, they found that they could make different parts of the dog's body move. Furthermore, they discovered an important and unexpected principle of brain activity. They found that stimulating the right side of the brain produced movement on the left side of the dog's body and vice versa. This finding stems from a general principle of how the brain is structured, calledcontrole contralateral. The brain is wired in such a way that, in most cases, the left hemisphere receives sensations and controls the right side of the body, and vice versa.

Fritsch and Hitzig also found that movement following brain stimulation only occurred when they stimulated a specific arcuate area that runs through the upper part of the brain from ear to ear, just in front of the parietal lobe (Figure \ (\Page index{ 11 }\)). Fritsch and Hitzig discovered the motor cortex,the part of the cortex that controls and executes body movements, sending signals to the cerebellum and spinal cord. Recent research has mapped the motor cortex even more completely, providing mild electronic stimulation to various areas of the motor cortex in fully conscious patients while observing their bodily responses (since the brain has no sensory receptors, these patients do not feel pain). As you can see in Figure \(\PageIndex{11}\), this research revealed that the motor cortex is specialized to provide control over the body, in the sense that the parts of the body that require finer and more precise movements, such as the face and hands also receive the greatest amount of cortical space.

Just as the motor cortex sends messages to specific parts of the body, the somatosensory cortex,an area just behind and parallel to the motor cortex at the back of the frontal lobe, receives input from sensory receptors in the skin and from the movements of various parts of the body. Again, the more sensitive the body region, the more area is devoted to it in the sensory cortex. Our sensitive lips, for example, occupy a large area of ​​sensory cortex, as do our fingers and genitals.

Other areas of the cortex process other types of sensory information. The visual cortex isthe area located in the occipital lobe (at the back of the brain) that processes visual information. If you were stimulated in the visual cortex, you would see flashes of light or color and might remember having the "seeing stars" experience when you were hit or dropped on the back of your head. The temporal lobe, located at the bottom of each hemisphere, contains the auditory cortex,responsible for hearing and language. The temporal lobe also processes visual information, giving us the ability to name objects around us (Martin, 2007).

As you can see in Figure \(\PageIndex{11}\), the motor and sensory areas of the cortex make up a relatively small part of the total cortex. The rest of the cortex consists of association areaseuwhat sensory and motor information is combined and connected with our stored knowledge. These association areas are the brain locations responsible for most of the things that make people appear human. The association areas are involved in higher mental functions such as learning, thinking, planning, judging, moral reflection, figuration, and spatial reasoning.

The brain is flexible: neuroplasticity

The control of some specific bodily functions such as movement, vision and hearing is carried out in specific areas of the cortex and if these areas are damaged, the individual is likely to lose the ability to perform the corresponding function. For example, if a child suffers damage to the facial recognition areas in the temporal lobe, it is likely that he will never be able to recognize faces (Farah, Rabinowitz, Quinn, & Liu, 2000). On the other hand, the brain is not completely rigidly divided. The brain's neurons have a remarkable ability to reorganize and expand to perform specific functions in response to the body's needs and to repair damage. As a result, the brain constantly creates new neural communication routes and reconnects existing ones. Neuroplasticity refers tothe brain's ability to change its structure and function in response to experience or injury. Neuroplasticity allows us to learn and remember new things and adapt to new experiences.

Our brains are most "plastic" when we are children, as that is when we learn the most about our environment. On the other hand, neuroplasticity continues to be observed even in adults (Kolb & Fantie, 1989). The principles of neuroplasticity help us understand how our brains evolve to reflect our experiences. For example, skilled musicians have a larger auditory cortex compared to the general population (Bengtsson et al., 2005) and also require less neural activity to move their fingers over the keys than novice musicians (Münte, Altenmüller, & Jäncke, 2002). These observations reflect changes in the brain that follow our experiences.

Plasticity is also seen when there is damage to the brain or body parts represented in the motor and sensory cortices. When a tumor in the left hemisphere impairs language, the right hemisphere begins to compensate to help the person regain the ability to speak (Thiel et al., 2006). And if a person loses a finger, the area of ​​the sensory cortex that previously received information from the missing finger will begin to receive information from adjacent fingers, causing the remaining fingers to become more sensitive to touch (Fox, 1984).

Although neurons cannot repair or regenerate like skin or blood vessels, new evidence suggests that the brain can be involved in neurogenesis,the formation of new neurons(Van Praag, Zhao, Gage, and Gazzaniga, 2004). These new neurons originate deep in the brain and can migrate to other areas of the brain, where they form new connections with other neurons (Gould, 2007). This opens up the possibility that one day scientists may "rebuild" damaged brains by creating drugs that help neurons grow.

Research Focus: Identifying the unique functions of the left and right hemispheres using split-brain patients

We have seen that the left hemisphere mainly senses and controls motor movements on the right side of the body and vice versa. This fact provides an interesting way to study brain lateralization -the idea that the left and right hemispheres of the brain are specialized to perform different functions. Gazzaniga, Bogen, and Sperry (1965) studied a patient, known as W.J., who had undergone surgery to relieve severe seizures. in this operationthe region that normally connects the two hemispheres of the brain and supports communication between the hemispheres, known as the corpus callosum, is cut. As a result, the patient essentially becomes one person with two separate brains. As the left and right hemispheres are separated, each hemisphere develops its own mind with its own sensations, concepts and motivations (Gazzaniga, 2005).

(Video) Rewiring the Anxious Brain: Neuroplasticity and the Anxiety Cycle: Anxiety Skills #21

In their research, Gazzaniga and colleagues tested W.J. to recognize and respond to objects and written passages presented only to the left hemisphere or only to the right (Figure \(\PageIndex{12}\)). The researchers made W.J. direct look and then they showed, for a fraction of a second, an image of a geometric shape to the left of where he was looking. By doing this, they ensured that - as the two hemispheres were separated - the image of the shape was only experienced in the right hemisphere (remember that sensory input from the left side of the body is sent to the right side of the brain). Gazzaniga and his colleagues discovered that W.J. was able to identify what had been shown when asked to select the object in a variety of ways using the left hand, but he was unable to do so when the object was shown on the right. field of vision. On the other hand, W.J. could easily read written material presented in the right visual field (and therefore experienced in the left hemisphere), but not when presented in the left visual field.

Information presented on the left side of our visual field is transferred to the right hemisphere and vice versa. In split-brain patients, the severed corpus callosum does not allow information to be transferred between the hemispheres, allowing researchers to learn about the functions of each hemisphere. In the sample on the left, the split-brain patient could not choose which image was presented because the left hemisphere cannot process visual information. In the right sample, the patient was unable to read the passage because the right hemisphere cannot process language.

This research and many other subsequent studies have shown that the two hemispheres of the brain are specialized for different skills. In most people, the ability to speak, write and understand language is located in the left hemisphere of the brain. That's why W.J. he could read passages presented on the right side and therefore transferred to the left hemisphere, but he could not read passages that were experienced only in the right hemisphere. The left hemisphere is also better at math and judging time and rhythm. It is also superior at coordinating the sequence of complex movements - for example, lip movements necessary for speech. The right hemisphere, on the other hand, has very limited verbal abilities but excels in perceptual abilities. The right hemisphere is capable of recognizing objects, including faces, patterns and melodies, and can put together a puzzle or draw a picture. That's why W.J. could select the image when he saw it in the left visual field but not in the right visual field.

Although Gazzaniga's research has shown that the brain is indeed lateralized, so that the two hemispheres specialize in different activities, this does not mean that when people behave in a certain way or perform a certain activity, they use only one. hemisphere of the brain at a time. . That would be a drastic simplification of the concept of brain differences. We often use both hemispheres at the same time, and the difference between the abilities of the two hemispheres is not absolute (Soroker et al., 2005).

main conclusions

• The ancient brain - including the brain stem, medulla, pons, reticular formation, thalamus, cerebellum, amygdala, hypothalamus and hippocampus - regulates basic survival functions such as breathing, movement, rest, eating, emotion and memory.
• The cerebral cortex, formed by billions of neurons and glial cells, is divided into right and left hemispheres and into four lobes.
• The frontal lobe is primarily responsible for thinking, planning, memory, and judgment. The parietal lobe is primarily responsible for bodily sensations and touch. The temporal lobe is primarily responsible for hearing and language. The occipital lobe is primarily responsible for vision. Other areas of the cortex act as association areas responsible for integrating information.
• The brain changes as a function of experience and potential injury in a process known as plasticity. The brain can generate new neurons through neurogenesis.
• The motor cortex controls voluntary movements. The parts of the body that require greater control and dexterity take up more space in the motor cortex.
• The sensory cortex receives and processes bodily sensations. The most sensitive body parts take up the most space in the sensory cortex.
• The left hemisphere is primarily responsible for language and speech in most people, while the right hemisphere specializes in spatial and perceptual skills, visualizing and recognizing patterns, faces and melodies.
• The separation of the corpus callosum, which connects the two hemispheres, creates a "split-brain patient", with the effect of creating two separate minds operating in one person.
• Studies with split-brain patients as research participants were used to study brain lateralization.
• Neuroplasticity allows the brain to adapt and change as a result of experience or injury.

Exercises and critical thinking

1. Do you think animals experience emotions? What aspects of brain structure might lead you to believe yes or no?
2. Consider your own experiences and speculate about which parts of your brain might be particularly well developed as a result of those experiences.
3. Which hemisphere of the brain are you likely to use when looking for a fork in the cutlery drawer? Which hemisphere of the brain are you likely to use when struggling to remember an old friend's name?
4. Do you think it's a good idea to encourage left-handed children to use their right hand? Why or why not?

References

Bengtsson, S.L., Nagy, Z., Skare, S., Forsman, L., Forssberg, H., & Ullén, F. (2005). Extensive piano practice has regionally specific effects on white matter development.Nature Neuroscience, 8(9), 1148-1150.

Best, B. (2009). The amygdala and emotions. INanatomy of mind(cap. 9). Retirado do site Welcome to the World of Ben Best:http://www.benbest.com/science/anatmind/anatmd9.html

Betancur, C., Velez, A., Cabanieu, G., & le Moal, M. (1990). Association between left-handedness and allergy: a reassessment.Neuropsychology, 28(2), 223-227.

Bodmer, W., & McKie, R. (1994).The Book of Man: The Quest to Uncover Our Genetic Inheritance. Londres, Inglaterra: Little, Brown and Company.

Bower, J.M., & Parsons, J.M. (2003). Rethinking the smaller brain.American Scientist, 289, 50-57.

Coren, S. (1992).The left-handed syndrome: the causes and consequences of left-handedness. Nova York, NY: Free Press.

de Courten-Myers, G.M. (1999). The human cerebral cortex: Sex differences in structure and function.Journal of Neuropathology and Experimental Neurology, 58, 217-226.

Dutta, T., & Mandal, M.K. (2006). Manual preference and accidents in India.Laterality: body, brain and cognition asymmetries, 11368-372.

Farah MJ, Rabinowitz C, Quinn GE, & Liu GT. (2000). Early involvement of neural substrates for facial recognition.Cognitive Neuropsychology, 17(1-3), 117-123.

Fox, J.L. (1984). The brain's dynamic way of keeping in touch.Science, 225(4664), 820-821.

Fritsch, G., & Hitzig, E. (2009). Electrical excitability of the brain.Epilepsy and behavior, 15(2), 123-130. (Original work published in 1870)

Gazzaniga MS, Bogen JE, & Sperry RW. (1965). Observations of visual perception after disconnection of the cerebral hemispheres in humans.brain, 88(2), 221-236.

Ge Schnell, N., & Behan, P. (2007).Left-handedness: association with immune disorders, migraine and developmental learning disorder. Cambridge, MA: MIT Press.

Gibson, K.R. (2002). Evolution of human intelligence: the roles of brain size and mental construction.Brain behavior and evolution 59, 10-20.

Gould, E. (2007). How widespread is adult neurogenesis in mammals?Nature Reviews Neuroscience 8,481-488. doi:10.1038/nrn2147

Harris, L.J. (1990). Cultural influences on crafts: theory and historical and contemporary evidence. In S. Coren (ed.),Left-handed: Implications and behavioral anomalies. New York, NY: Elsevier.

Hepper, P.G., Wells, D.L., & Lynch, C. (2005). Prenatal finger-sucking is related to postnatal handedness.Neuropsychology, 43313-315.

Ida, Y., & Mandal, M.K. (2003). Cultural differences in lateral bias: evidence from Japan and India.Laterality: body, brain and cognition asymmetries, 8(2), 121-133.

Jones, G.V., & Martin, M. (2000). A note on Corballis (1997) and the genetics and evolution of handedness: developing a unified distribution model from the sex chromosome gene hypothesis.Psychological Review, 107(1), 213-218.

Klüver, H., & Bucy, P.C. (1939). Preliminary analysis of temporal lobe functions in monkeys.Archives of Neurology and Psychiatry (Chicago), 42, 979-1000.

Kolb, B., & Fantie, B. (1989). Development of the child's brain and behavior. In C. R. Reynolds & E. Fletcher-Janzen (Eds.),Handbook of Child Clinical Neuropsychology(pp. 17–39). New York, NY: Plenum Press.

Olds, J. (1958). Brain self-stimulation: its use in studying the local effects of starvation, sex, and drugs.Science, 127315-324.

Martin, A. (2007). The representation of object concepts in the brain.Annual Review of Psychology, 58, 25-45.

McKeever, W.F., Cerone, L.J., Suter, P.J., & Wu, S.M. (2000). Family size, propensity to miscarry and handedness: testing hypotheses of the developmental instability theory of handedness.Laterality: body, brain and cognition asymmetries, 5(2), 111-120.

McManus, I.C. (2002).Right hand, left hand: the origins of asymmetry in brains, bodies, atoms and cultures. Cambridge, MA: Harvard University Press.

Miller, G. (2005). Neuroscience: The dark side of glia.Science, 308(5723), 778-781.

Münte, T.F., Altenmüller, E., & Jäncke, L. (2002). The musician's brain as a model of neuroplasticity.Nature Reviews Neuroscience, 3(6), 473-478.

Olds, J. & Milner, P. (1954). Positive reinforcement produced by electrical stimulation of the septal area and other areas of the rat brain.Journal of Comparative and Physiological Psychology, 47419-427.

Peters, M., Reimers, S., & Manning, J.T. (2006). Handwriting preference and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC Internet Study.Brain and Cognition, 62(2), 177-189.

Sherman, S.M., & Guillery, R.W. (2006).Exploring the thalamus and its role in cortical function(2nd edition). Cambridge, MA: MIT Press.

Sigurdsson, T., Doyere, V., Cain, C.K., & LeDoux, J.E. (2007). Long-term potentiation in the amygdala: a cellular mechanism for fear learning and memory.Neurofarmakologi, 52(1), 215-227.

Soroker, N., Kasher, A., Giora, R., Batori, G., Corn, C., Gil, M., & Zaidel, E. (2005). Treatment of basic speech acts after localized brain injury: new light on the neuroanatomy of language.Brain and Cognition, 57(2), 214-217.

Springer, S.P. & Deutsch, G. (1998).Left brain, right brain: Perspectives from cognitive neuroscience(5th edition). A series of psychology books. New York, NY: W. H. Freeman/Times Books/Henry Holt & Co.

Thiel A, Habedank B, Herholz K, Kessler J, Winhuisen L, Haupt WF, & Heiss WD. (2006). Left to right: How the brain compensates for progressive loss of language function.Brain and language, 98(1), 57-65.

Van Praag, H., Zhao, X., Gage, F.H., & Gazzaniga, M.S. (2004). Neurogenesis in the adult mammalian brain. INcognitive neuroscience(3rd edition, pp. 127–137). Cambridge, MA: MIT Press.