Posts Tagged ‘PET’

Suggestible You 7

March 23, 2017

“Suggestible You” is the title of a book by Erik Vance.  The subtitle is “The Curious Science of Your Brain’s Ability to Deceive, Transform, and Heal.  This post is about the placebo response and related phenomena.   This is the seventh post on this book.

This post is about hypnosis.  During the late 50s and early 60s researchers at Stanford and Harvard came up with 12-step scales to quantify how suggestible to hypnosis someone is.  Their research led these researchers to conclude that hypnotic susceptibility is a fixed trait.  Susceptibility to hypnosis doesn’t change much  from late adolescence until death.  The most spectacular  forms of hypnosis  work only on the most hypnotizable 10% or so of the population.  Another 10% do not respond to hypnosis at all, and 80% fall somewhere in between.

A Canadian psychologist Pierre Rainville successfully hypnotized one group not to feel any pain from hot water poured on their hands and another group to believe that they could feel pain but that it would not bother them.  Their brains were scanned with positron emission tomography (PET) and found two very different neural reactions to pain.  This suggested that the sensation of pain and the emotions associated with it have separate triggers as well a how crucial emotion is to our experience of pain.  There is also neurological evidence that there are two different pathways for pain.  One dealing with the response to the pain itself, and the second to the interpretation of the pain.  It is this latter response that characterized chronic pain.  See the previous healthy memory blog posts “Pain and the Second Dart,”  “To Treat Chronic Pain, Look to the Brain Not Body,” and “Controlling Pain in Our Minds.”

Rainville’s work indicates that hypnosis often involves parts of the brain associated with attention, emotion regulation, and pain.  People seem  to be wired differently for hypnosis, and that this doesn’t change much over the course of our lives.  Research has also shown that the capacity to be hypnotized is not tied to intelligence or willpower.

Some tend to think of hypnosis as being another placebo.  The consensus  is that they are not related.  Hypnotic susceptibility remains relatively stable throughout one’s life, whereas placebo responsiveness can change from day to day.  And the drug naloxone, which is effective at blocking placebo responses doesn’t block hypnosis.  So although they are not the same, they both tap into a deep force in the brain:  expectation.

Psychologist Marcel Kinsbourne says, “There is a wave of bottom-up information coming up from the external world, up into your brain.  There is a wave of information coming from the cortex that consists of your evaluations, your beliefs, your expectations.  Consciousness is these two waves hitting each other.  It’s a collision.  And this is where hypnosis and placebos do their work.”


How Can The Brain Be Imaged?

November 20, 2009

Technologies that allow us to view what is going on inside the brain are a fairly new and exciting development. This blog provides a very brief explanation of these techniques. There will be frequent references to this blog in future presentations of brain imaging studies.

One of the first techniques was Positron Emission Tomography (PET). PET imaging requires that a radioactive substance called a radiotracer been injected into the bloodstream. This radiotracer makes its way into the brain. The level of radioactivity is extremely low so that the individual undergoing the imaging is not put at risk. The individual lies down within the PET imaging machine and is asked to perform different tasks. A computer processes the data to produce 2- or 3 – dimensional images. The images show blood flow and oxygen and glucose metabolism in the tissues of the brain. These images reflect the amount of brain activity in the different regions of the brain.

Functional Magnetic Resonance Imaging (fMRI) is a more recent development that does not require the injection of radioisotopes into the blood stream. It is an enhancement of Magnetic Resonance Imaging where the individual lies on a table with her head inside a giant magnet. Protons inside the atoms in the brain align themselves with the magnetic field and are wacked temporarily out of alignment by a pulse of radio waves aimed at the brain. As the protons relax back into alignment again, they emit radio waves that a computer uses to create a brain snapshot. fMRI takes advantage of two more facts about the body: (1) blood contains iron and (2) blood rushes to a specific part of the brain when it is activated. As freshly oxygenated blood zooms into a region, the iron distorts the magnetic field enough for the scanner to pick it up.

Prior to the development of these imaging techniques, researchers were restricted to recording electrical activity in the brain from the scalps of humans. Still much valuable data was obtained and these techniques are still used today. Event-related potentials (ERPs) are electrical waveforms that are elicited by specific sights, sounds, or other stimuli. The P300 is a bump in the electrical waveform that occurs within one-third of a second after a person is exposed to a word or some other external stimulus. This heightened activity reflects the additional processing that the brain devotes to novel, distinctive events. Larger P300s tend to be associated with greater subsequent recall.[1]

[1] Reported in Schacter (1996).  Searching for memory:  the brain, the mind, and the past.    New York:  Basic Books.   p. 55.