The Buying Brain: Secrets for Selling to the Subconscious Mind (9 page)

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electrical impulses along their axons (which range in length from a tenth of an inch to three feet or more!), this electrical current produces tiny voltage changes across the neuron’s cell membrane. These small but highly predictive, sometimes chaotic and noisy, and at other times regular electrical changes allow us to measure with precision how the brain reacts to any stimuli, from medical conditions to marketing messages. But more about that later. We have a bit more to learn about the brain in light of recent scientific breakthroughs.

So, back to the neuron. When a nerve impulse is initiated, a dramatic reversal in the electrical potential occurs at one point on the cell’s membrane, when the neuron switches from an internal negative charge to a positive charge. This change, called an
action potential
, then passes along the membrane of the axon at speeds of up to 100 miles per hour. At this dramatic speed, a neuron can fire impulses up to about 1,000 times a second.

When they reach the end of an axon, these voltage changes trigger the release of
neurotransmitters
, the brain’s chemical messengers.

Neurotransmitters are released by nerve terminals and bind to receptors on the surface of the target cell. These receptors then act as on-and-off switches for the next cell. There may be tens of thousands of such connections on a neuron modifying the target cell, which has to compute inputs from many cells that contact it—tens of thousands of connections, a thousand times a second in a binary and algorithmic computational dance. Amazing!

How Neurons Gather into Functional

Areas of the Brain

Neurons connect with each other and with distant muscle and gland cells.

These connections form trillions of specific patterns that re-form, grow, and migrate over the course of our lives.

This spectacular neuron specification and migration begins in the human embryo, where the right types of neurons must form in significant numbers to complete their preordained tasks and then must migrate to the appropriate places to form functional units that make up the brain. After they’ve reached their destination, which could be inches or feet from where they started, the neurons extend axons and dendrites to connect to each other.

Remarkably, the axons are then guided, even pulled, by the targets they will
activate.

For example, a newly-born neuron that has migrated to the motor area of the brain will extend its axon to the bottom of the spinal cord where it will P1: OTA/XYZ

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target another motor cell that will then control the muscle that moves your big toe. If nurtured properly by its target, that pathway then thrives and functions in a neurochemical partnership.

Birth of Neurons

About four weeks after conception, the ridges on the flat plane of the embryo fold, and fuse to form the hollow neural tube. This primitive structure grows and evolves in truly spectacular fashion, with the fetal brain at times producing a quarter of a million new neurons
every day
. In addition to neurons, the mature nervous system contains glial cells, which clean up leftover chemical transmitters, guide migrating neurons, and serve as the infamous blood/brain barrier, which prevents toxins in the blood from killing brain tissue.

Neurons collect together to form each of the various brain structures, acquire specific ways of transmitting nerve messages, and learn unique ways to process and control interactions with the environment, from motor tasks (like throwing a ball) to complex memory tasks (like guiding a submarine).

After its spectacular period of growth in the fetus, the neural network is pared back to create a more efficient system. Neurons are removed when they lose their battle with other neurons to receive life-sustaining chemical signals produced by the target tissues. So the same cells that draw them forward, in many cases, then deprive them of life. This pruning process explains why
children actually have more brain cells than adults.

Those extra brain cells also form too many connections at first. In humans and other primates, children have twice the number of connections between neurons that adults have. For example, the neural connections between the two eyes and the brain initially overlap, but then migrate to separate territories devoted to one eye or the other. The connections that are active and generating electrical currents survive, whereas those neurons with little or no activity fade away. Thus, the circuits of the adult brain are formed, at least in part, by sculpting away incorrect or unused connections to leave only the correct ones, in the most elemental example of “use it or lose it.”

What’s left is a precisely elaborated adult network of 100 billion neurons capable of body movement, perception, emotion, and thought.

Once the neurons reach their final location in the brain, they must make the proper connections for a particular function to occur, such as vision or hearing. They do this through their axons. These thin appendages can stretch out a thousand times longer than the cell body from which they arise, from one side of the brain to the other. The journey of most axons ends when they P1: OTA/XYZ

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meet thicker appendages, called dendrites, of other neurons. Enlargements of the axon’s tip, called growth cones, actively explore the environment as they seek out their precise destination.

Once axons reach their targets, they form synapses, which permit electric signals
in the axon to jump to the next cell, where they can either provoke or prevent the
generation of a new signal.

Each neuron receives thousands of synapses, and the astounding information-processing power of the brain works by turning on or off the huge number of electric signals that pass through the synapses.

The human brain is what makes us human.

Every Neuron Has a Target

As they grow and begin to migrate throughout the body, each neuron makes connections at a precise point with a specific target. Each neuron somehow knows to bypass all other points and other targets, and arrives at a destination that is predetermined to fit that neuron and that neuron alone.

Once in place in its network, the neuron generates an action potential (an electrical current) along the axon in response to stimuli. The current may be tiny (from a few microvolts), fast (up to 100 meters a second), or powerful and permanent. Once the cell body has summed all the inputs that excite or inhibit an electrical current, the neuron fires off its action potential. Once fired, it
goes
! The action potential carries the same voltage all the way to its target destination. These action potentials give us great insight into the impact a given stimulus, perhaps a television commercial, or a brand logo, has made on the brain.

Parts of the Brain

The growth, migration, and pruning of neurons leaves them in remarkably purposeful sections of the brain, each dedicated to finely-tuned and interdependent functions that run a body and make a mind.

For this section of Brain 101, let’s start at the top with the cerebral cortex.

This part of the brain is divided into four large regions: the occipital lobe, the

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Figure 4.2

Major parts of the brain.

Source:
Courtesy by Acxiom Corporation, Wellsphere.com temporal lobe, the parietal lobe, and the frontal lobe (see Figure 4.2). Functions, such as vision, hearing, and speech, are distributed in these regions. Some regions perform more than one function. And assigning a specific function with a specific region is a less than perfect science as we are all subtly different and that is reflected in our brains’ organization. For instance, in an amputee, just after losing a limb, the brain’s neurons still represent that body part, even though the limb isn’t there. Later that representation fades away as other adjacent limb functions migrate over or begin to activate into that valuable tissue.

The cerebral cortex performs
the highest intellectual functions
—thinking, planning, and problem solving. The
hippocampus
is involved in memory. The thalamus serves as a relay station for almost all the information coming into the brain. Neurons in the hypothalamus—the master of the master gland—serve as relay stations for internal regulatory systems—body temperature, eating, mating—by monitoring information coming in from the nervous system and issuing orders to the body through those nerves and the pituitary or “master” gland.

On the upper surface of the midbrain are two pairs of small hills that are called colliculi, collections of cells that relay sensory information from sense P1: OTA/XYZ

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organs to the brain. The hindbrain consists of the pons and medulla oblongata, which help control respiration and heart rhythms, and the cerebellum, which helps control movement as well as cognitive processes that require precise timing.

Where do memories live?
It’s an interesting question. Many studies of human and animal memory have led scientists to conclude that no single brain center stores memory. It most likely is stored in distributed collections of brain processing systems—the same systems that are involved in the perception, processing, and analysis of the material being learned. In short, many parts of the brain contribute to permanent memory storage. For example, the hippocampus, parahippocampal region, and areas of the cerebral cortex (including the prefrontal cortex) compose a system that supports declarative, or cognitive, memory, such as remembering phone numbers. Different forms of behavioral memory, such as knowing how to throw a ball, are supported by the amygdala, striatum, and cerebellum.

Language

One of the most important human abilities is language, a complex system involving many components, including sensory motor functions and memory systems. Although the neural basis of language is not fully understood, scientists have learned a great deal about this function of the brain from studies of patients who have lost speech and language abilities owing to stroke, traumatic brain injury, and also from brain imaging studies of normal people. It has long been known that damage to different regions within the left hemisphere (in most right-handed people) produce different kinds of language disorders, or aphasias.

Researchers once believed that all aspects of language ability were governed only by the left hemisphere. Recognition of speech sounds and words, however, involves both left and right temporal lobes. In contrast, speech production is a strongly left-dominant function. However, the emotional content in speech, which comes via voice inflection, is a mostly right hemispheric (emotional hemisphere) function.

Sections of the Brain Work Together Like a
Highly Coordinated Team

The brain handles many mental functions through multiple regions. For example, the brain pathways used to read words are different from those we use to hear or speak them. Still another pathway gives us the meaning of P1: OTA/XYZ

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the word. The more pathways that are involved, the more complicated the action becomes. Prosody—or the tone of voice we use when we speak that lets others know whether we’re happy, sad, or excited—originates in the right hemisphere of the brain. But the logical content of language, for example, that

“the truck is red,” originates in the left hemisphere.

In fact,
all
mental functions can be divided into subfunctions that work interdependently to give us a representation of consciousness and self. Perception, language, thought, movement, and memory all link to multiple regions of the brain. That’s why the entire brain must be measured to catch these electrical impulses as the separate regions “talk to” and react with each other.

Each Section Interacts with the Next

The final discovery in our tour of the brain is that each part of the brain interacts with its neighbors, creating topographical maps that science can use to find disorders and lesions. A final interesting but imperative fact: The functional systems on one side of the brain control the opposite side of the body. So the sensory/motor activations on the left side of the body are mediated by the cerebral hemisphere on the right side of the body.