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Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Chapter 3 Biological Psychology Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Biological Psychology In this chapter we will examine: What are the components of the nervous system? How does the brain create mental processes and behavior? “What we understand least is why brain activity produces experience at all.” -- James W. Kalat Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Module 3.1 Neurons and Behavior Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Introduction Reductionism? Scientists in many fields use a strategy called reductionism; they attempt to explain complex phenomena by reducing them to combinations of simpler components. Chemists use atoms and molecules; physicists reduce the subatomic world to the interactions of a few fundamental forces. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Introduction Reductionism? Does reductionism work in the science of psychology? Let’s find out as we try to explain behavior in terms of the activity of the cells that comprise the nervous system. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Neurons You experience yourself as a unitary entity. Neuroscientists have demonstrated that that experience is the product of a nervous system made up of an enormous number of discrete cells. The cells that make up your nervous system are called neurons. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.1 Distribution of the estimated 100 billion neurons in the adult human central nervous system. (Based on data of R. W. Williams & Herrup, 1988) Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Neurons and communication Neurons are a unique type of cell that can receive and transmit information electrochemically. Sensory neurons carry information from sense organs to the central nervous system. Neurons in the central nervous system process that information, interpret it, and then send commands to muscles, glands and organs. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells The best current estimate is that the human nervous system has nearly 100 billion neurons. And they aren’t the only type of cell in the system. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Glia Glia support the neurons in many ways. They provide insulation, and remove waste products and foreign bodies. They are 1/10th the size of the neurons, but about 10 times as numerous. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Anatomy of a neuron Neurons have a variety of shapes, but they all have 3 basic parts. A cell body that contains the nucleus and most of the organelles. The dendrites, widely branching structures that receive transmissions from other neurons. The axon, which is a single, long, thin fiber with branches near its tip. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Axons The function of the axon is to send the electrochemical message on to the next cell. Most axons transmit information to the dendrites or cell bodies of neighboring neurons. Many axons have a coating of myelin, which speeds up transmission. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Nerve cell growth Neurons do not have a fixed anatomy. Researchers have discovered that neurons are constantly growing and losing branches to dendrites and axons. This growth seems to be related to new experiences and learning. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials Axons convey information by a combination of electrical and chemical processes. This combination is called an action potential. An action potential is an excitation that travels along the axon at a constant strength regardless of the distance it must travel. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials The all-or-none law An action potential is an all-or-nothing process – it’s either happening or not; there’s no “sort of” action potential. This allows the message to reach the brain at full strength, but does slow it down compared to regular electrical conduction. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials How an action potential works: An un-stimulated axon has resting potential. Resting potential is an electrical polarization across the membrane covering the axon. A polarized axon has an inside charge that is negative (-70 millivolts) relative to the outside. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials How an action potential works: Resting potential is maintained by the mechanism called the sodium-potassium pump. Sodium is mostly concentrated outside the neuron, and potassium mostly inside, and they are held in place by special “gates” while the polarization is maintained by the action of the pump. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.4 The sodium and potassium gradients for a resting membrane. Sodium ions are concentrated outside the neuron; potassium ions are concentrated inside. Because of the negatively charged protein ions inside the neuron, the inside of the cell is negatively charged relative to the outside of the cell. Protein and chloride ions (not shown) bear negative charges inside the cell. At rest, very few sodium ions cross the membrane except by the sodium-potassium pump. Potassium tends to flow into the cell because of an electrical gradient, and tends to flow out because of the concentration gradient. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials How an action potential works: The sodium-potassium pump sends positively charged (+1) sodium ions out of the cell and brings in a smaller number of positively charged (+1) potassium ions. The result is that the outside of the cell has more positive charges than the inside. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials How an action potential works: When a message from a neighboring cell excites part of the axon’s membrane, some of the sodium gates are opened and sodium can enter the axon. This makes the charge inside the cell positive. Depolarization has taken place. The charge is now briefly the same inside and outside the cell. This is the action potential. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.6 (a) During an action potential, sodium gates in the neuron membrane open, and sodium ions enter the axon, bringing a positive charge with them. (b) After an action potential occurs at one point along the axon, the sodium gates close at that point and open at the next point along the axon. When the sodium gates close, potassium gates open, and potassium ions flow out of the axon, carrying a positive charge with them. (Modified from Starr & Taggart, 1992) Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.6 (a) During an action potential, sodium gates in the neuron membrane open, and sodium ions enter the axon, bringing a positive charge with them. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.6 (b) After an action potential occurs at one point along the axon, the sodium gates close at that point and open at the next point along the axon. When the sodium gates close, potassium gates open, and potassium ions flow out of the axon, carrying a positive charge with them. (Modified from Starr & Taggart, 1992) Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Action potentials How an action potential works: The sodium gates shut very quickly and potassium gates open to allow potassium ions to leave the cell. These ions take the positive charge out with them, and bring the axon back to a polarized state. Eventually the action of the sodium-potassium pump removes the excess sodium ions and recaptures the exiled potassium ions. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check If a hamster and a seven-foot-tall human step on a sharp object, which will respond faster? Why? The hamster, because the action potential has a shorter distance to travel. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Synapses Communication between neurons occurs at the synapses. A synapse is a specialized junction between two neurons where chemical messages cross from one to the other. The chemicals released by one will either excite or inhibit the other, making it either more or less likely to produce an action potential. This activity at the synapses is crucial to everything the brain does. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Synaptic transmission The electrochemical messages carried by neurons either increase or decrease the likelihood that the next cell will continue to transmit. Excitatory messages increase the probability that the next cell will “fire” - continue to carry the transmission. Inhibitory messages decrease the likelihood that transmission will continue to travel – as in the case of the brain sending a message to inhibit pain in an injured extremity. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.8 The synapse is the junction of the presynaptic (message-sending) cell and the postsynaptic (message-receiving) cell. At the end of the presynaptic axon is the terminal bouton (or button), which contains many molecules of the neurotransmitter, ready for release. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Synapses Synaptic communication: Each axon has a bulge at the end called a presynaptic ending or a terminal bouton (alternately spelled “button.”) When the action potential reaches the terminal bouton, molecules of a neurotransmitter are released. A neurotransmitter is a chemical that is stored in the neuron. It activates special receptors of other neurons. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Synapses Synaptic communication: Neurons use a variety of neurotransmitters, but each individual neuron always uses a particular neurotransmitter or combination of them. The neurotransmitter diffuses over the synapse to the surface of the receiving neuron (called the postsynaptic neuron.) The neurotransmitter attaches to receptors on the dendrite or cell body of the receiving neuron and either excites or inhibits it. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.9 The complex process of neural communication actually takes only 1–2 milliseconds. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Nervous System Cells Synapses Synaptic communication: After the neurotransmitter has excited or inhibited the receiving cell, it detaches from the receptor site, ending the message. The neurotransmitter may be reabsorbed by the axon that released (a process called reuptake) or diffuse away, be metabolized and removed from the body as a waste product, or remain the synapse and reattach to the receptor. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Learning and environmental challenges sometimes produce branching in axons and dendrites of an organism’s neurons. How would that affect the number of synapses? It would increase the number of synapses. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Dopamine is a neurotransmitter that excites postsynaptic neurons. If a drug were injected into an animal that blocked dopamine from attaching to its receptors, what would happen to the postsynaptic neurons? They would be less likely to produce further action potentials. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Neurotransmitters and Behavior Our understanding of the role of neurotransmitters has revolutionized medicine, particularly psychiatry. A drug that can be designed to act on a particular kind of receptor in the nervous system can also have specific effects on an organism’s functioning and behavior. It can be hypothesized that unusual behavior or problems in functioning may be due to lack or excess of a particular neurotransmitter. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Neurotransmitters and Behavior Parkinson’s disease Parkinson’s disease is a condition in which the individual has trouble executing voluntary movements, and has tremors, rigidity and a depressed mood. This condition has been linked to a gradual decay in a system of axons that release the neurotransmitter dopamine. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Neurotransmitters and Behavior Parkinson’s disease Dopamine is a neurotransmitter that promotes activity levels and facilitated movement. Symptoms of Parkinson’s disease can be managed in mild cases with a drug called L-dopa, which is synthesized into dopamine by the neurons. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.11With Parkinson’s disease, axons from the substantia nigra gradually die. (a) Normal brain (b) Brain of person with Parkinson’s disease. Green = excitatory path; red = inhibitory. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Neurotransmitters and Behavior The link is not always so clear though. The symptoms of a disorder such as attention-deficit disorder or ADD include impulsive, agitated behavior and a short attention span. These symptoms would suggest an oversupply of dopamine. But there doesn’t seem to be any relationship between dopamine and ADD. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check People suffering from schizophrenia are given haloperidol, a drug that blocks activity at dopamine synapses. How would haloperidol affect a person with Parkinson’s Disease? It would make the symptoms worse. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Neurotransmitters and Behavior The neurotransmitter, whether it is in over-, under- or normal supply, is just one part of a complex system. What alleviates the problem may not necessarily tell us what originally caused the problem. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Module 3.2 The Nervous System and Behavior Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Major Divisions of the Nervous System The central nervous system and the peripheral nervous system The central nervous system consists of the brain and the spinal cord. The central nervous system communicates with the rest of the body via the peripheral nervous system. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.12 The nervous system has two major divisions: the central nervous system and the peripheral nervous system. Each of these has major subdivisions, as shown. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Major Divisions of the Nervous System The central nervous system and the peripheral nervous system The peripheral nervous system is composed of bundles of axons between the spinal cord and the rest of the body. There are two sets of subdivisions of the peripheral nervous system. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Peripheral Nervous System The somatic nervous system and autonomic nervous system The somatic nervous system is made up of the peripheral nerves that communicate with the skin and muscles. The autonomic nervous system controls the involuntary actions of the heart, stomach and other organs. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Central Nervous System Embryological development During the embryonic stage, the vertebrate nervous system forms out of a simple tube with three lumps: The forebrain that becomes the cerebral cortex and other higher structures. The midbrain and hindbrain become the brainstem. The forebrain is especially dominant in human beings. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.13 The human brain begins development as three lumps. By birth the forebrain has grown much larger than either the midbrain or the hindbrain, although all three structures perform essential functions. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain General structure The forebrain The forebrain has two separate hemispheres, left and right. Each hemisphere controls sensation and motor functioning on the opposite side of the body. The hemispheres of the brain communicate with each other through a thick bundle of axons crossing between them, called the corpus callosum. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Cerebral cortex The cerebral cortex The outer covering of the forebrain is known as the cerebral cortex. It is made up of the gray matter, the cell bodies of the cortical neurons. The interior of the forebrain is made up of white matter or axons of cortical neurons. It is white because of the myelin that coats axons. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Cerebral cortex The four lobes of the cerebral cortex It’s customary to represent the areas of the cerebral cortex as four lobes: occipital, parietal, temporal, and frontal. The occipital lobe is at the rear of the head, and contains many specialized areas for interpreting visual sensory information. There are areas both inside and outside the occipital lobes for shape, color and motion vision. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Cerebral cortex The four lobes of the cerebral cortex The parietal lobe is directly in front of the occipital lobe. It contains the primary somatosensory cortex, the area of the brain that is specialized for body senses and awareness of the location of body parts. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Cerebral Cortex The four lobes of the cerebral cortex The temporal lobes are located on the sides of the head, near the ears. They are the main processing areas for hearing and complex aspects of vision. The left temporal lobe contains important areas for language processing and comprehension. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Other structures that lie under or near the temporal lobe include the hypothalamus, amygdala and hippocampus. The hypothalamus helps to regulate emotional and motivated behavior. The amygdala, an almond-shaped structure that is crucial for emotional processing, is deep inside the temporal lobes. The hippocampus is a vital structure for memory processing. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Forebrain Cerebral cortex The four lobes of the cerebral cortex The frontal lobes are at the front of the brain. They contain the primary motor cortex, and area that is important for control of fine movements. The foremost part of the frontal lobes, the prefrontal cortex, is responsible for organization, planning of action, and aspects of memory. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.17 The four lobes of the human cerebral cortex, with indications of some of their major functions. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Which lobe is damaged if… A person is unable to feel or locate the left side of her body? Right parietal lobe Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Which lobe is damaged if… A person has difficulty with fine movements with the right hand? Left frontal lobe Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Which lobe is damaged if… A person has loss of vision in the right visual field? Left occipital lobe Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Concept Check Which lobe is damaged if… A person has impaired emotional experience and some hearing loss? Temporal lobe Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Between the Spinal Cord and the Forebrain The hindbrain & midbrain The medulla, pons and midbrain contain the reticular activating system (or reticular formation). This structure regulates levels of arousal in the brain. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology How the Cerebral Cortex Communicates with the Body The hindbrain The cerebellum is important for coordination and timing. It is also in charge of tasks that requiring shifting of attention and discrimination between stimuli. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology How the Cerebral Cortex Communicates with the Body The hindbrain The medulla oblongata and the pons are two important structures in the hindbrain. They contain the axons that control breathing and heart rate. They are also in charge of relaying sensory information from the head and sending motor messages back to it. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.14 (a) The major divisions of the human central nervous system, as seen from the midline. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology How the Cerebral Cortex Communicates with the Body The spinal cord The spinal cord Both reflex and voluntary responses are conducted through the spinal cord. A reflex is a rapid, automatic response to a stimulus. The spinal cord is usually the origination point of these responses. A voluntary response originates in the brain and travels through the spinal cord to the muscles needed to carry out the movements. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology How the Cerebral Cortex Communicates with the Body The spinal cord The spinal cord The spinal cord communicates with the body below the head by means of sensory and motor neurons. The sensory neurons carry information received by the senses from the extremities of the body to the spinal cord. The motor neurons transmit messages from the central nervous system to the muscles and glands. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.20 The spinal cord receives sensory information from all parts of the body except the head. Motor nerves in the spinal cord send messages to control the muscles and glands. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Peripheral Nervous System The autonomic nervous system The autonomic nervous system A division of the peripheral nervous system that is closely associated with the spinal cord is the autonomic nervous system. The individual has very little control over the responses in this division, thus the name, autonomic. The autonomic nervous system has two subdivisions. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Peripheral Nervous System The autonomic nervous system The divisions of the autonomic nervous system The sympathetic nervous system is the crisis management center. It increases heart and respiration rate and prepares the body for fight or flight. A chain of neurons lying just outside the spinal cord controls it. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Peripheral Nervous System The autonomic nervous system The divisions of the autonomic nervous system The parasympathetic nervous system is in charge of long-term survival related functions, nutrition and energy conservation. It decreases heart rate, increases digestive activities and promotes processes in the body that take place during rest. It is controlled by neurons at the upper and lower levels of the spinal cord. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.21 The sympathetic nervous system prepares the body for brief bouts of vigorous activity; the parasympathetic nervous system promotes digestion and other nonemergency functions. Although both systems are active at all times, the balance can shift from a predominance of one to a predominance of the other. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Endocrine System The endocrine system is under the control of the nervous system. The endocrine system is a system of glands that release hormones into the bloodstream. Hormones are chemicals that affect mood, behavior and even anatomy. Some neurotransmitters act as hormones when released into the bloodstream. An example of one of these is epinephrine, which is called adrenaline when it is acting as a hormone. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.22 Glands in the endocrine system produce hormones and release them into the bloodstream. This shows only some of the endocrine glands and some of their most abundant hormones. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Measuring brain activity Methods for looking at and mapping the brain include: Electroencephalographs and Magnetoencephalographs (EEGs and MEGs) record electrical and magnetic activity in the brain. These readouts do not allow the viewing of brain activity. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Measuring brain activity Methods for looking at and mapping the brain include: Positron emission tomography (PET) provides a highresolution picture of brain activity using radioactivity from chemicals injected into the bloodstream. The color of the image indicates the level of activity: red areas are most active, followed by yellow, green and blue for the least active areas. PET scans provide fascinating information, but are expensive and can be risky to the subject. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Measuring brain activity Methods for looking at and mapping the brain include: Functional magnetic resonance imaging (fMRI) uses magnetic detectors outside the head to measure the amounts of hemoglobin and oxygen in different areas of the brain. Highly active areas of the brain appear to use more oxygen in fMRI images. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Experience and the Brain Nerve cell generation Neurons can be generated later in life (to a limited extent). It was once thought that all neurons developed well before birth. Researchers have discovered stem cells undifferentiated cells growing in some brain areas that are capable of developing into neurons in older organisms. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Experience and the Brain Nerve cell generation Neuronal generation is generally very limited in scope. The action of stem cells seems to be stimulated after some types of brain damage, so their purpose may be in part compensatory. The growth of new neurons is much more limited than that which occurs in skin and hair cells. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Experience and the Brain Learning changes the brain We now know, because we can “see” the brain, and its activity that practicing behaviors (learning to play a musical instrument, for example) can change the structure of the brain by altering the cortical neurons. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Experience and the Brain The “binding problem” We still don’t understand precisely how all the different parts of the brain allow us to have a unified experience of objects or events, since the areas of the brain that help us analyze our experience are often not directly connected to each other. It is amazing that people can lose just one aspect of vision, for example, color, motion, or the ability to recognize faces. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Experience and the brain The two halves of the brain Work with individuals who have had the “split-brain” operation (severing the corpus callosum) to control seizures provides evidence that the two hemispheres are highly specialized. The right hemisphere needs to communicate with the left in order to name the objects in its visual field. The left hemisphere needs the right in order to synthesize details into a whole picture (the parts of a face into a whole recognizable image). Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.26 The corpus callosum is a large set of axons that convey information between the two hemispheres of the cerebral cortex. (a) A midline view showing the location of the corpus callosum. (b) A horizontal section showing how each axon of the corpus callosum links one spot in the left hemisphere to a corresponding spot in the right hemisphere. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.27 In the human visual system (viewed here from above), light from either half of the world crosses through the pupils to strike the opposite side of each retina. Axons from the left half of each retina travel to the left hemisphere of the brain; axons from the right half of each retina travel to the right hemisphere of the brain. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology Figure 3.28 (a) A man with a severed corpus callosum cannot name something he sees in his left visual field but can find the corresponding object with his right hand. (b) When the word hatband is flashed on a screen, a man with a split brain can report only what his left hemisphere saw, “band.” However, with his left hand he can point to a hat, which is what the right hemisphere saw. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Brain and the Self We are still learning about the brain, but we now understand that your brain is composed of many separate areas with separate abilities. Introduction to Psychology, 7th Edition, James W. Kalat Chapter 3: Biological Psychology The Brain and the Self If you lose part of the brain, you lose part of your unique experience. Brain activity and mind are inseparable. One is the other.