The Future of the Mind Read Online Free PDF Page B

“almond.”
    •  The thalamus. This is like a relay station, gathering sensory signals from the brain stem and then sending them out to the various cortices. Its name means “inner chamber.”
    •  The hypothalamus. This regulates body temperature, our circadian rhythm, hunger, thirst, and aspects of reproduction and pleasure. It lies below the thalamus—hence its name.
    Finally, we have the third and most recent region of the mammalian brain, the cerebral cortex, which is the outer layer of the brain. The latest evolutionary structure within the cerebral cortex is the neocortex (meaning “new bark”), which governs higher cognitive behavior. It is most highly developed in humans: it makes up 80 percent of our brain’s mass, yet is only as thick as a napkin. In rats the neocortex is smooth, but it is highly convoluted in humans, which allows a large amount of surface area to be crammed into the human skull.
    In some sense, the human brain is like a museum containing remnants of all the previous stages in our evolution over millions of years, exploding outward and forward in size and function. (This is also roughly the path taken when an infant is born. The infant brain expands outward and toward the front, perhaps mimicking the stages of our evolution.)
    Although the neocortex seems unassuming, looks are deceiving. Under a microscope you can appreciate the intricate architecture of the brain. The gray matter of the brain consists of billions of tiny brain cells called neurons. Like a gigantic telephone network, they receive messages from other neurons via dendrites, which are like tendrils sprouting from one end of the neuron. At the other end of the neuron, there is a long fiber called the axon. Eventually the axon connects to as many as ten thousand other neurons via their dendrites. At the juncture between the two, there is a tiny gap called the synapse. These synapses act like gates, regulating the flow of information within the brain. Special chemicals called neurotransmitters can enter the synapse and alter the flow of signals. Because neurotransmitters like dopamine, serotonin,and noradrenaline help control the stream of information moving across the myriad pathways of the brain, they exert a powerful effect on our moods, emotions, thoughts, and state of mind. (See Figure 4 .)
    This description of the brain roughly represented the state of knowledge through the 1980s. In the 1990s, however, with the introduction of new technologies from the field of physics, the mechanics of thought began to be revealed in exquisite detail, unleashing the current explosion of scientific discovery. One of the workhorses of this revolution has been the MRI machine.

    Figure 4 . Diagram of a neuron. Electrical signals travel along the axon of the neuron until they hit the synapse. Neurotransmitters can regulate the flow of electrical signals past the synapse. ( illustration credit 1.4 )
    THE MRI: WINDOW INTO THE BRAIN
    To understand the reason why this radical new technology has helped decode the thinking brain, we have to turn our attention to some basic principles of physics.
    Radio waves, a type of electromagnetic radiation, can pass right through tissue without doing damage. MRI machines take advantage of this fact, allowing electromagnetic waves to freely penetrate the skull. In the process, this technology has given us glorious photographs of something once thought to be impossible to capture: the inner workings of the brain as it experiences sensations and emotions. Watching the dance of lights flickering in a MRI machine, one can trace out the thoughts moving within the brain. It’s like being able to see the inside of a clock as it ticks.
    The first thing you notice about an MRI machine is the huge, cylindrical magnetic coils, which can produce a magnetic field twenty to sixty thousand times greater than the strength of Earth’s. The giant magnet is one of the principal reasons why an MRI machine can weigh a ton,