Читать книгу Why It Hurts - Dr. Aneesh Singla - Страница 17

Let’s consider simple, anatomic reasons for pain, like a stubbed toe or a paper cut. In his Treatise of Man, 17th-century French philosopher René Descartes proposed the existence of a “hollow tube” transmitting the pain sensation from the location of the injury to the brain. Fundamentally speaking, today’s pain specialists concur with Descartes in that they believe:

1 Nerves detect a painful sensation.

2 Those nerves transmit a pain signal to the brain.

3 By interrupting that signal we can stop the perception of pain.

Thus, we inject substances or prescribe medications that reduce a nerve’s ability to transmit pain to achieve pain reduction.

This model works quite well for physical pain, or pain “with a cause.” It leads us to seek out a focal, physical source of pain and treat it. However, the Cartesian model fails miserably when dealing with the psychological aspects of pain. For example, a person on a battlefield can sustain a horrific injury and perceive little or no pain and then experience agony in the hospital afterward during a simple needle injection. (We’ll cover this idea more in Chapter 4.)

If we identify a physical pain generator, like an area of inflammation, we can treat it through a combination of techniques with the goal of improving the patient’s functionality and reducing the level of pain with the lowest-risk intervention. When we can’t find a clear pain generator, we come to the conclusion that the nervous system is sending a false alarm and we attempt to tone down the general sensitivity of the pain signaling system.

While Descartes was in many ways a visionary when it comes to pain, our ideas on the subject have evolved substantially since the 1600s. Patrick Wall, mentioned earlier, and Canadian psychologist Ronald Melzack proposed the gate control theory of pain in 1965. They described a series of nerve pathways (peripheral, spinal cord, and brain) that allow us to perceive pain. According to their theory, while a pain signal is transmitted, there is potential for gates to be opened along these pathways, allowing for modulation of the intensity of the pain signal.

Although there are shortcomings in the gate control theory of pain, there are some benefits to this conceptual model over the simple Cartesian view of simple circuits that are either on or off. More recently, others have proposed a multidimensional model of pain in which three distinct areas combine to form one perception of pain: sensory (what we physically feel as pain), affective (how we feel emotionally about that pain), and cognitive (what we ultimately think about the pain based on our value system, cultural context, and so on).

None of these models perfectly describe how we perceive pain, but each sheds some light on a phenomenally complex area of human experience.