24 THE STUDENT'S GUIDE TO COGNITIVE NEUROSCIENCE membrane which either pump positive or negative ions.thus making an 尚 action potential more or less likely Other common neurotransmitters are serotonin.dopamine.acetylcholine and noradrenaline.These are often considered to have modulatory functions.Rather than being distributed ONLINE RESOURCE throughout the brain,as is the case with GABA and glutamate.the cell bodies of the neurons that release these neurotransmitters tend to he localized to s neuroscience basics? but their axonal projectionsspread Take a look at the How do neurons code information? neuroscience crash lrde of an action potential does not vary,but the otentials pr second varies alor ontinuum This course and a free als calle h。 ng e relat of Neuroscience rried by th 80 s (e.g. speech not others ve a comp to be ary profile types to the functiona ation of brain regions th was int ation is car ied in the responserate of a neuron,what determine he type of inform o?The ype of t to oth th ary audit cortex can be considered to carry informati out sound is b cause the input from a pathway originating in th cochlea and ney information to other neurons involve d in more advanced stages of auditory e were to rewe the retinal pathway,originating in the eyes,rather than the auditory pathway (Sur Leamey,2001).In this case,the function of the primary auditory cortex would have changed (as would the type of information it carries)even though the region itself was not directly modified (only the inputs to it were KEY TERMS modified).This general point is worth bearing in mind when one considers what the function of a given region is.The function of a region is determined by its inputs and outputs.As such,the extent to which a function can be strictly localized is a moot point. ly of ne White matter THE GROSS ORGANIZATION OF THE BRAIN Tissue of the nervou Gray matter,white matter and cerebrospinal fluid cells Neurons are organized within the brain to form white matter and gray matter 1 Gray matter consists of neuronal cell bodies.White matter consists of axons ort cells of the and support cells(glia).The brain consists of a highly convoluted folded in tissue repair and in sheet of gray matter(the cerebral cortex),beneath which lies the white matter In the center of the brain,beneath the bulk of the white matter fibers,lies another collection of gray matter structures(the subcortex),which includes the basal ganglia,the limbic system and the diencephalon
24 THE STUDENT’S GUIDE TO COGNITIVE NEUROSCIENCE membrane which either pump positive or negative ions, thus making an action potential more or less likely. Other common neurotransmitters are serotonin, dopamine, acetylcholine and noradrenaline. These are often considered to have modulatory functions. Rather than being distributed throughout the brain, as is the case with GABA and glutamate, the cell bodies of the neurons that release these neurotransmitters tend to be localized to specific brain areas, but their axonal projections spread diffusely throughout the brain. How do neurons code information? The amplitude of an action potential does not vary, but the number of action potentials propagated per second varies along a continuum. This rate of responding (also called the “spiking rate”) relates to the informational “code” carried by that neuron. For example, some neurons may have a high spiking rate in some situations (e.g., during speech), but not others (e.g., during vision), whereas other neurons would have a complementary profile. Neurons responding to similar types of information tend to be grouped together. This gives rise to the functional specialization of brain regions that was introduced in Chapter 1. If information is carried in the response rate of a neuron, what determines the type of information that the neuron responds to? The type of information that a neuron carries is related to the input it receives and the output it sends to other neurons. For example, the reason neurons in the primary auditory cortex can be considered to carry information about sound is because they receive input from a pathway originating in the cochlea and they send information to other neurons involved in more advanced stages of auditory processing (e.g., speech perception). However, imagine that one were to rewire the brain such that the primary auditory cortex was to receive inputs from the retinal pathway, originating in the eyes, rather than the auditory pathway (Sur & Leamey, 2001). In this case, the function of the primary “auditory” cortex would have changed (as would the type of information it carries) even though the region itself was not directly modified (only the inputs to it were modified). This general point is worth bearing in mind when one considers what the function of a given region is. The function of a region is determined by its inputs and outputs. As such, the extent to which a function can be strictly localized is a moot point. THE GROSS ORGANIZATION OF THE BRAIN Gray matter, white matter and cerebrospinal fluid Neurons are organized within the brain to form white matter and gray matter. Gray matter consists of neuronal cell bodies. White matter consists of axons and support cells (glia). The brain consists of a highly convoluted folded sheet of gray matter (the cerebral cortex), beneath which lies the white matter. In the center of the brain, beneath the bulk of the white matter fibers, lies another collection of gray matter structures (the subcortex), which includes the basal ganglia, the limbic system and the diencephalon. ONLINE RESOURCE Do you need to get up to speed on your neuroscience basics? Take a look at the companion website (www.routledge. com/cw/ward) for links to a YouTube neuroscience crash course and a free online Fundamentals of Neuroscience module from Harvard University. KEY TERMS Gray matter Matter consisting primarily of neuronal cell bodies. White matter Tissue of the nervous system consisting primarily of axons and support cells. Glia Support cells of the nervous system involved in tissue repair and in the formation of myelin (among other functions)
INTRODUCING THE BRAIN 25 FIGURE 2.4:There are three different kinds of white matter tract,depending on (ort emher) teortcalbeRmeenHembpherl FIGURE 2.5:The brain consists of four ventricles lled with cerebrospinal teortoledoubatcal each hemisphere,the third ventricle lies centrally around in the brainstem (hindbrain). Front view Side view mde Lateral ventricle aiea
Introducing the brain 25 FIGURE 2.4: There are three different kinds of white matter tract, depending on the nature of the regions that are connected. Adapted from Diamond et al., 1986. © 1986 by Coloring Concepts, Inc. Reprinted by permission of HarperCollins Publishers. FIGURE 2.5: The brain consists of four ventricles filled with cerebrospinal fluid (CSF): the lateral ventricles are found in each hemisphere, the third ventricle lies centrally around the subcortical structures and the fourth ventricle lies in the brainstem (hindbrain)
26 THE STUDENT'S GUIDE TO COGNITIVE NEUROSCIENCE KEY TERMS White matter tracts may project between different cortical regions within the same hemisphere(called association tracts).or project between different cortical regions in different hemispheres (called commissures:the most important commissure being the corpus callosum)or may project betw een that connects the two hemispheres. cortical and subcortical structures(called projection tracts ee Figure 2.4. The brain also contains a number of hollow chambers termed ve /entricles shown in Figure 2.5.These were incorrectly revered for 1.500 vears as being the brain that contain the seat of mental life.The ventricles are filled with cerebr cerebrospinal fluid. which does serve some useful functions,albeit non-cognitive.The CSFcarr waste metabolites transfers some messenger sig and provides a protective Toward the front. cushion for the brain. Posterior Toward the back A hierarchical view of the central nervous system Superfor Toward the top. Baincoltioncambethoueghtofasadingaditionalstnetwresoaiooldc ather tha ep om ob olde p on (se Dorsal paihwaysalboe ways con: he rm or Toward the top for other spe illustr e majo Ventral the br g4 Toward the bottom. ateral The outer part (cf.medial). Terms of reference and section Medial In or toward the middle wes and posterior refer to direct ns toward the front and back f the brain inferior.respectively they are also known as dorsal and ventral,respectively.The terms anterior posterior,superior and inferior (or rostral,caudal,dorsal and ventral)enable navigation in two dimensions:front-back and top-bottom(see Figure 2.7) Needless to say,the brain is three-dimensional and so a further dimension is required.The terms lateral and medial are used to refer to directions toward the outer surface and the center of the brain,respectively,although"medial is ambiguous,because it is also used in another context.Although it is used to refer to the center of the brain,it is also used to refer to the middle of structures more generally.For example,the medial temporal gyrus lies on the lateral surface of the brain(not the medial surface).It is labeled medial because it lies midway between the superior and inferior temporal gyri. The brain can be sectioned into two-dimensional slices in a number of ways,as shown in Figure 2.8.A coronal cross-section refers to a slice in the vertical plane through both hemispheres(the brain appears roundish in this section).A sagittal section refers to a slice in the vertical plane going through one of the hemispheres.When the sagittal section lies between the hemispheres it is called a midline or medial section.An axial (or horizontal) section is taken in the horizontal plane
26 THE STUDENT’S GUIDE TO COGNITIVE NEUROSCIENCE White matter tracts may project between different cortical regions within the same hemisphere (called association tracts), or project between different cortical regions in different hemispheres (called commissures; the most important commissure being the corpus callosum) or may project between cortical and subcortical structures (called projection tracts)—see Figure 2.4. The brain also contains a number of hollow chambers termed ventricles, shown in Figure 2.5. These were incorrectly revered for 1,500 years as being the seat of mental life. The ventricles are filled with cerebrospinal fluid (CSF), which does serve some useful functions, albeit non-cognitive. The CSF carries waste metabolites, transfers some messenger signals and provides a protective cushion for the brain. A hierarchical view of the central nervous system Brain evolution can be thought of as adding additional structures onto older ones, rather than replacing older structures with newer ones. For example, the main visual pathway in humans travels from the retina to the occipital lobe, but a number of older visual pathways also exist and contribute to vision (see Chapter 7). These older pathways constitute the dominant form of seeing for other species such as birds and reptiles. Figure 2.6 illustrates the major structures of the brain, showing a hierarchical arrangement (older structures toward the bottom of the diagram). Terms of reference and section There are conventional directions for navigating around the brain, just as there is a north, south, east and west for navigating around maps. Anterior and posterior refer to directions toward the front and back of the brain, respectively. These are also called rostral and caudal, respectively, particularly in other species that have a tail (caudal refers to the tail end). Directions toward the top and bottom are referred to as superior and inferior, respectively; they are also known as dorsal and ventral, respectively. The terms anterior, posterior, superior and inferior (or rostral, caudal, dorsal and ventral) enable navigation in two dimensions: front–back and top–bottom (see Figure 2.7). Needless to say, the brain is three-dimensional and so a further dimension is required. The terms lateral and medial are used to refer to directions toward the outer surface and the center of the brain, respectively, although “medial” is ambiguous, because it is also used in another context. Although it is used to refer to the center of the brain, it is also used to refer to the middle of structures more generally. For example, the medial temporal gyrus lies on the lateral surface of the brain (not the medial surface). It is labeled medial because it lies midway between the superior and inferior temporal gyri. The brain can be sectioned into two-dimensional slices in a number of ways, as shown in Figure 2.8. A coronal cross-section refers to a slice in the vertical plane through both hemispheres (the brain appears roundish in this section). A sagittal section refers to a slice in the vertical plane going through one of the hemispheres. When the sagittal section lies between the hemispheres it is called a midline or medial section. An axial (or horizontal) section is taken in the horizontal plane. KEY TERMS Corpus callosum A large white matter tract that connects the two hemispheres. Ventricles The hollow chambers of the brain that contain cerebrospinal fluid. Anterior Toward the front. Posterior Toward the back. Superior Toward the top. Inferior Toward the bottom. Dorsal Toward the top. Ventral Toward the bottom. Lateral The outer part (cf. medial). Medial In or toward the middle
INTRODUCING THE BRAIN 27 Frontal cortex Ce Temporal cortex Parietal cortex Occipital cortex Cingulatecortex Amygdala teleephalonl aae Basal ganglia Putamen Forebrai Thalamus Brain Diencephalon Hypothalamus Mamillary bodies Substantia nigra Midbrain ord Cerebellum Hindbrain →Pons Medulla FIGURE2.6:The。 organized hierarchically.The upper lev s of the hi are the newest structures from an evolutionary (ad FIGURE 2.7:Temms o (referring to the outer nferio
Introducing the brain 27 FIGURE 2.6: The central nervous system (CNS) is organized hierarchically. The upper levels of the hierarchy, corresponding to the upper branches of this diagram, are the newest structures from an evolutionary perspective. FIGURE 2.7: Terms of reference in the brain. Note also the terms lateral (referring to the outer surface of the brain) and medial (referring to the central regions)
28 THE STUDENT'S GUIDE TO COGNITIVE NEUROSCIENCE KEY TERMS Sagittal Anterio cortex. Coronal Sulci(sulcus=singular) oenegoeson Anterio FIGURE 2.9:The main gyri of the lateral (top)and FIGURE 2.8:Terms of sectio s of the brain sulci tend to be labeled according to terms of THE CEREBRAL CORTEX For e The cerebral cortex consists of two folded sheets of gray matter organized medial temporal gyri. into two hemispheres (left and right).The surface of the cortex has become increasingly more convoluted with evolutionary development.Having a folded structure permits a high surface area to volume ratio and thereby permits efficient packaging. The raised surfaces of the cortex are termed ueo gyri (o The cortex is only around 3 mm thick and when viewed in cross-section reflectthe grouping of differentcelltypes Differ parts of the cortex have different densities in each of the layers Most of the cortex contains six main cortical lav te med the (mea new Othe (including e are and the alloc x(inc primary olfact x and hi p of mpus) ortex of each is divided four occipital o lobe by the sylvian fissure). bu 1 other 28 19 y De (e.g- 201 temporal and obes) Othe regions of the cortex are observable only in a
28 THE STUDENT’S GUIDE TO COGNITIVE NEUROSCIENCE THE CEREBRAL CORTEX The cerebral cortex consists of two folded sheets of gray matter organized into two hemispheres (left and right). The surface of the cortex has become increasingly more convoluted with evolutionary development. Having a folded structure permits a high surface area to volume ratio and thereby permits efficient packaging. The raised surfaces of the cortex are termed gyri (or gyrus in the singular). The dips or folds are called sulci (or sulcus in the singular). The cortex is only around 3 mm thick and is organized into different layers that can be seen when viewed in cross-section. The different layers reflect the grouping of different cell types. Different parts of the cortex have different densities in each of the layers. Most of the cortex contains six main cortical layers, termed the neocortex (meaning “new cortex”). Other cortical regions are the mesocortex (including the cingulate gyrus and insula) and the allocortex (including the primary olfactory cortex and hippocampus). The lateral surface of the cortex of each hemisphere is divided into four lobes: the frontal, parietal, temporal and occipital lobes (Figure 2.9). The dividing line between the lobes is sometimes prominent, as is the case between the frontal and temporal lobes (divided by the lateral or sylvian fissure), but in other cases, the boundary cannot readily be observed (e.g., between temporal and occipital lobes). Other regions of the cortex are observable only in a FIGURE 2.8: Terms of sections of the brain. Adapted from Diamond et al., 1986. © 1986 by Coloring Concepts Inc. Reprinted by permission of HarperCollins Publishers. KEY TERMS Gyri (gyrus = singular) The raised folds of the cortex. Sulci (sulcus = singular) The buried grooves of the cortex. FIGURE 2.9: The main gyri of the lateral (top) and medial (bottom) surface of the brain. The cortical sulci tend to be labeled according to terms of reference. For example, the superior temporal sulcus lies between the superior and medial temporal gyri