The brain is contained within the cranium, and constitutes the upper, greatly expanded part of the central nervous system. Henry Gray (1918) Looking through the gray outer layer of the cortex, you can see a mass of white matter. At the center is a cluster of large nuclei, including the basal ganglia, the hippocampi, the amygdalae, and two egg-shaped structures at the very center, barely visible in this figure, the thalami. The thalami rest on the lower brainstem (dark and light blue). You can also see the pituitary gland in front (beige), and the cerebellum at the rear of the brain (pink). In this chapter we will take these structures apart and re-build them from the bottom up. 09_P375070_Ch05.indd 126 1/29/2010 4:08:25 AM CHAPTER 5 The brain OUTLINE 1.0 Introduction 127 3.2 Output and input: the front-back division 143 1.1 The nervous system 128 3.3 The major lobes: visible and hidden 145 1.2 The geography of the brain 129 3.4 The massive interconnectivity of the cortex and thalamus 149 2.0 Growing a brain from the bottom up 133 3.5 The satellites of the subcortex 151 2.1 Evolution and personal history are expressed in the brain 133 4.0 Summary 153 2.2 Building a brain from bottom to top 134 5.0 Chapter review 153 3.0 From ‘ where ’ to ‘ what ’ : the functional 5.1 Study questions 153 roles of brain regions 136 5.2 Drawing exercises 153 3.1 The cerebral hemispheres: the left-right division 136 1.0 INTRODUCTION found. While knowledge of the brain is constantly expanding, we will focus on the basics. Our brains give us our biggest evolutionary edge. Cognitive neuroscience inevitably focuses on the Other large mammals have bigger muscles and greater cortex, often considered to involve the ‘ highest level ’ speed, but humans have an exceptionally big and flex- of processing. The cortex is only the outer and vis- ible brain, specialized for excellent vision and hear- ible portion of an enormous brain, one that has devel- ing, language and social relationships, and for manual oped over hundreds of millions of years of evolution. control and flexible executive control. Human brains The word ‘ cortex ’ means bark , since that was how it make culture and technology possible. appeared to early anatomists. While the cortex is vital In this chapter, we look at the structure of the brain, for cognitive functions, it interacts constantly with while in the coming chapters we will cover its func- major ‘ satellite ’ organs, notably the thalamus, basal tions – how it is believed to work. It is important to ganglia, cerebellum, hippocampus, and limbic regions, understand that brain anatomy is not a static and among others. The closest connections are between settled field: new and important facts are constantly the cortex and thalamus, which is often called the tha- being discovered. On the microscopic and nanoscopic lamo-cortical system for that reason. In this core system levels, whole new classes of neurons, synapses, con- of the brain, signal traffic can flow flexibly back and nection patterns, and transmitter molecules have been forth, like air traffic across the earth. Cognition, Brain, and Consciousness, edited by B. J. Baars and N. M. Gage ISBN: 978-0-12-375070-9 © 20102010 Elsevier Ltd. All rights reserved. 127 09_P375070_Ch05.indd 127 1/29/2010 4:08:25 AM 128 5. THE BRAIN The major lobes of cortex are comparable to the make the connections between cortical neurons look earth’s continents, each with its population centers, nat- white to the naked eye. ural resources, and trade relations with other regions. While cortical regions are often specialized, they are 1.1 The nervous system also densely integrated with other regions, using web- like connections that spread throughout the cortex and The brain is part of the nervous system which per- its associated organs. This outer sheet is called the gray vades the human body. The two main parts are the matter from the way it looks to the naked eye. It is the central nervous system (CNS), which includes the outer ‘ skin ’ of the white matter of cortex which appears brain and the spinal cord, and the peripheral nerv- to fill the large cortical hemispheres, like the flesh of a ous system (PNS), which contains the autonomic and fruit. However, this is only appearance. In fact, the gray peripheral sensory and motor system ( Figure 5.1 ). matter contains the cell bodies of tens of billions of Together the CNS and PNS provide a dynamic and neurons that send even larger numbers of axons in all massive communication system throughout all parts directions, covered by supportive myelin cells that are of the body, with a hub at the brain that is accessed filled with white lipid molecules. These white myelin through the spinal cord. We will focus in this chapter sheaths of cortical neurons are so pervasive that they on one part of the CNS, the brain ( Figure 5.2 ). Peripheral nervous Central nervous system (PNS) system (CNS) Brain Cranial nerve Spinal Spinal cord nerve FIGURE 5.1 The central and peripheral nervous systems. FIGURE 5.2 Parts of the central nervous system include the Source : Standring, 2005. spinal cord and the brain. Source : Standring, 2005. 09_P375070_Ch05.indd 128 1/29/2010 4:08:26 AM 1.0 INTRODUCTION 129 In this chapter, we will focus on two sensory and hearing have been most studied in the human input systems within the brain: vision and hearing. brain. We will focus on two output systems, speech Although there are other sensory input systems, such and hand-arm control, again because they have been as olfaction (smell) and somatosensory (touch), vision the target of much study. Throughout this chapter on the brain, we will describe the anatomy of the brain and brain regions and we will also highlight the func- tion they serve. We will begin with discussing the many levels of analysis that we can take in describing the brain – from large-scale regions such as cerebral hemispheres and cortical lobes, to finer-scale classifi- cations, such as cortical layer topography. 1.2 The geography of the brain Let ’s begin with the large-scale brain areas and work our way down to a finer analysis. First, to state the rather obvious, the brain is located in the human head, as depicted in Figure 5.3 . We can look at the brain at different geographical levels – from continents to countries, states, and cities. Thus, we have several levels of detail. The first dis- tinct geographical regions are the two cerebral hemi- spheres, which are entirely separate, joined through a complex connective region called the corpus callosum. We will discuss the hemispheres in more detail later in the chapter: the question of why we have two separate hemispheres in the brain has long intrigued scientists and philosophers alike. Next , we have the cortical lobes ( Figure 5.4 ): there are four lobes in each hemisphere. Beginning at the FIGURE 5.3 The location of the brain in the head, showing a midsagittal view of the right hemisphere. FIGURE 5.4 The four major lobes of the cortex are visible from a lateral view of the brain. Here we show a view of the left hemisphere with the frontal lobe (purple) at the anterior of the brain, the parietal lobe (orange) posterior to the frontal lobe at the superior aspect of the brain, the temporal lobe (blue) posterior to the frontal lobe and inferior to the parietal lobe, and the occipital lobe (yellow) posterior to both the pari- etal and temporal lobes. Just below the occipital lobe is the cerebellum (green), which is not part of the cortex but is visible from most aspects of the brain. Source : Squire et al ., 2003. 09_P375070_Ch05.indd 129 1/29/2010 4:08:30 AM 130 5. THE BRAIN gyrus ntal al lobule fro s centr Med or u Su ara ial ri c pe P fr e ulcus l ri on up tal s u s s or us tal ron s u u s p e g S f l r u I a Parieto-occipital n y or y lc r s ntra r u r ri a y u pa ie c u e r g u c r t re gulate s p l t g l ie a sulcus in su u nta l s l u sul ta l P C lcu S ro n a l cu l l s f r a s s o le e t a r l b r t d c u s n t gyrus id ru n a le late y e r I gu M e n t n g r e fer Cin c e c n g io P t r r e e C p r s a lo c b a o t s P m ul ri s callosum s u e u P a r e rp r t s o us o y a C yr p u l g P g e ta u r n on S r s a u f . I l s r u s io c u C r u t s h fe m m g r A n a ra n y us m I r ulc ior A g s u Pars ter ne s Pos ri Pars opercularis al gyrus Latera lca rus or us l Ca gy P re mp sulc occip s al a triangularis su r te oral ita u gu ra fis rio mp sulc l lc in h l pe r te us u L ip ra u io s po Pars e S r e Collater c t pe us t al su a a u l gyr a lc m orbitalis L S pora us p em n al g id t us u M yr M ulc L ed us mp ral s ial o ior te o cci fer yrus pito In ral g tem po L po Subcallosal area tem atera Oc ral rior l oc cipi gy Infe ci totem rus pito po s tem ral sulcu Uncus poral g yrus Rhinal sulcus FIGURE 5.5 Some important landmarks of the brain in the left hemisphere from a lateral perspective (left panel) and a midsagittal perspective (right panel).