The Central Nervous System: Making Sense of the World 61 ■ What evidence would help to evaluate the alternatives? As technology continues to be reﬁned, the quality of fMRI scans will continue to improve, giving us ever better images of where brain activity is taking place. But the value of this scanning technology will depend on a better understanding of what it can and cannot tell us about how brain activity is related to behavior and mental processes. We also need more evidence about correlation and causation in fMRI research. For example, a recent study conducted fMRI scans on compulsive gamblers as they played a simple guessing game (Reuter et al., 2005). When they won the game, these people showed an unusually small amount of activity in a brain area that is normally activated by the experience of rewards, or pleasure. Noting the correlation between compulsive gambling and lower-than-normal activity in the reward area, the researchers suggested that an abnormality in the brain’s reward mechanisms might be responsible for gambling addiction. But recent case studies also suggest that compulsive gambling appears in people taking a prescription drug that increases activity in reward areas—and that the gambling stops when the drug is discontinued (Dodd et al., 2005). As noted in the chapter on introducing psychology, correlation does not guarantee causation. Is the brain activity reﬂected in fMRI scans causing the thoughts and feelings that take place during the scanning process? Possibly, but those thoughts and feelings might themselves be caused by activity elsewhere in the brain that affects the areas being scanned. Reaching an understanding about questions like these will require continuing debate and dialogue between those who dismiss fMRI and those who sing its praises. To make this interaction easier, a group of government agencies and private foundations has recently funded an fMRI Data Center (http://www.fmridc.org/f/fmridc). This facility stores information from fMRI experiments and makes it available to both critics and supporters of fMRI, who can review the research data, conduct their own analyses, and offer their own interpretations. Having access to an ever-growing database such as this will no doubt help scientists get the most out of fMRI technology while also helping each other to avoid either overstating or underestimating the meaning of fMRI research. ■ What conclusions are most reasonable? When the EEG was invented nearly 100 years ago, scientists had their ﬁrst glimpse of brain cell activity, as reﬂected in the “brain waves” traced on a long sheet of paper rolling from the EEG machine (see Figure 4.3). To many of these scientists, EEG must have seemed a golden gateway to an understanding of the brain and its relationship to behavior and mental processes. EEG has, in fact, helped to advance knowledge of the brain, but it certainly didn’t solve all of its mysteries. When all is said and done, the same will probably be true of fMRI. It is an exciting new tool, and it offers previously undreamed-of images of the structure and functioning of the brain, but it is unlikely on its own to explain just how the brain creates our behavior and mental processes. It seems reasonable to conclude, then, that those who question the use of fMRI to study psychological processes are right in calling for a careful analysis of the value of this important high-tech tool. Although the meaning of fMRI data will remain a subject for debate, there is no doubt that brain scanning techniques in general have opened new frontiers for biological psychology, neuroscience, and medicine (Goldstein & Volkow, 2002; Miller, 2003). Let’s now explore some of the structures highlighted by these techniques, starting with three major subdivisions of the brain: the hindbrain, the midbrain, and the forebrain. The Hindbrain hindbrain The portion of the brain that lies just inside the skull and is a continuation of the spinal cord. Figure 2.8 shows the major structures of the brain. The hindbrain lies just inside the skull and is actually a continuation of the spinal cord. Incoming signals from the spinal cord ﬁrst reach the hindbrain. Many vital autonomic functions, such as heart rate, 62 FIGURE Chapter 2 Biology and Behavior 2.8 Brain Major Structures of the Brain This side view of a section cut down the middle of the brain reveals the forebrain, midbrain, hindbrain, and spinal cord. Many of these subdivisions do not have clear-cut borders, because they are all interconnected by ﬁber tracts. The brain’s anatomy reﬂects its evolution over millions of years. Newer structures (such as the cerebral cortex, which is the outer surface of the forebrain) that handle higher mental functions were built on older ones (such as the medulla) that coordinate heart rate, breathing, and other more basic functions. Forebrain Midbrain Hindbrain Reticular formation Cerebellum Medulla Spinal cord medulla The area of the hindbrain that controls vital autonomic functions such as heart rate, blood pressure, and breathing. reticular formation A collection of cells and ﬁbers in the hindbrain and midbrain that are involved in arousal and attention. cerebellum The part of the hindbrain that controls ﬁnely coordinated movements. blood pressure, and breathing, are controlled by nuclei in the hindbrain, particularly in an area called the medulla (pronounced “meh-DU-lah”). Weaving throughout the hindbrain and into the midbrain is a mesh-like collection of cells called the reticular formation (reticular means “net-like”). This network is involved in arousal and attention. Cutting off ﬁbers of the reticular system from the rest of the brain would put a person into a permanent coma. Some of the ﬁbers that carry pain signals from the spinal cord connect in the reticular formation and immediately arouse the brain from sleep. Within seconds, the hindbrain causes your heart rate and blood pressure to increase. You are awake and aroused. The cerebellum (pronounced “sair-a-BELL-um”) is also part of the hindbrain. For a long time its primary function was thought to be control of ﬁnely coordinated movements, such as threading a needle. We now know that the cerebellum also allows the eyes to track a moving target accurately (Krauzlis & Lisberger, 1991) and that it may be the storehouse for well-rehearsed movements, such as those associated with dancing, playing a musical instrument, and athletics (McCormick & Thompson, 1984). The cerebellum might also be involved in the learning of these skills (Hazeltine & Ivry, 2002), as well as in more uniquely human tasks such as language and abstract thinking (Bower & Parsons, 2003). For instance, abnormalities in the cerebellum have been associated with reading disabilities (Rae et al., 2002), and surgery that affects the cerebellum sometimes results in a syndrome called cerebellar mutism, in which patients become unable to speak for periods ranging from a few days to several years (Gelabert-Gonzalez & Fernandez-Villa, 2001). In short, the cerebellum seems to be involved in both physical and cognitive agility. Reﬂexes and feedback systems are important in the hindbrain. For example, if blood pressure drops, heart action reﬂexively increases to make up for that decrease. If you stand up quickly, your blood pressure can drop so suddenly that you feel lightheaded until the hindbrain reﬂexively “catches up.” You will faint if the hindbrain does not activate the autonomic nervous system to increase your blood pressure.