Photo courtesy of the NIDA Web site. From Teaching Packet: The Brain and the Actions of cocaine, Opiates, and Marijuana.

5: Control centers in the brain are affected by drug use.

Drugs of abuse disable or disrupt important brain functions.

When someone smokes marijuana, for example, the chemical THC (delta-9-tetrahydrocannabinol), the main psychoactive ingredient in marijuana, travels quickly to the brain. We can see the areas of the brain (in dark blue) where THC concentrates. Let’s go back to the previous image and see the areas of the brain that are affected by THC.

[PRESENTER: Please return to the previous image and point out these areas.]

You can see that THC builds up in areas that control the body’s movements, balance, coordination, memory and judgment abilities, and sensations. THC disrupts your brain’s ability to control these activities as well as you could normally.

Now let’s take a look inside your mind... One of the tools that scientists use to see the effects of drugs on the brain is called positron emission tomography or a PET [say the word “pet”] scan. Similar to an x-ray, but much more sophisticated, a PET scan is used to examine many different organs including the heart, liver, lungs, and bones, as well as the brain. A PET scan shows much more than the physical structure of bone and tissue. A PET scan shows how well (or how little) an organ is functioning.
 
Using a PET scan, a doctor or a scientist can see what is actually happening in a person’s brain and see the effects of drugs. The PET scan shows areas of the brain that are active and also areas that are inactive or not functioning at all. Typically, a PET scan takes 1 to 2 hours with the person lying completely still so that the PET images will be clear.
 
Let’s see the effects a drug like cocaine has on the brain.

Photo courtesy of Nora Volkow, Ph.D. Mapping cocaine binding sites in human and baboon brain in vivo. Fowler JS, Volkow ND, Wolf AP, Dewey SL, Schlyer DJ, Macgregor, Hitzemann R, Logan J, Bendreim B, Gatley ST, et al. Synapse 1989;4(4):371-377.

When someone gets "high" on cocaine, where does the cocaine go in the brain? With the help of a radioactive tracer, this PET scan shows us a person's brain on cocaine and the area of the brain, highlighted in yellow, where cocaine is "binding" or attaching itself. This PET scan shows us minute by minute, in a time-lapsed sequence, just how quickly cocaine begins affecting a particular area of the brain

We start in the upper left hand corner. You can see that 1 minute after cocaine is administered to this subject nothing much happens. All areas of the brain are functioning normally. But after 3 to 4 minutes [the next scan to the right], we see some areas starting to turn yellow. These areas are part of a brain structure called the striatum [stry-a-tum] that is the main target in the brain bound and activated by cocaine.

At the 5- to 8-minute interval, we see that cocaine is affecting a large area of the brain. After that, the drug's effects begin to wear off. At the 9- to 10-minute point, the high feeling is almost gone. Unless the abuser takes more cocaine, the experience is over in about 20 to 30 minutes.

Scientists are doing research to find out if the striatum produces the "high feeling" and controls our feelings of pleasure and motivation. One of the reasons scientists are curious about specific areas of the brain affected by drugs such as cocaine is to develop treatments for people who become addicted to these drugs. Scientists hope to find the most effective way to change an addicted brain back to normal functioning.

Photo courtesy of Nora Volkow, Ph.D. Volkow ND, Hitzemann R, Wang G-J, Fowler JS, Wolf AP, Dewey SL. Long-term frontal brain metabolic changes in cocaine abusers. Synapse 11:184-190, 1992; Volkow ND, Fowler JS, Wang G-J, Hitzemann R, Logan J, Schlyer D, Dewey S, Wolf AP. Decreased dopamine D2 receptor availability is associated with reduced frontal metabolism in cocaine abusers. Synapse 14:169-177, 1993.

This PET scan shows us that once addicted to a drug like cocaine, the brain is affected for a long, long time. In other words, once addicted, the brain is literally changed. Let’s see how...
 
In this image, the level of brain function is indicated in yellow. The top row shows a normal-functioning brain without drugs. You can see a lot of brain activity. In other words, there is a lot of yellow color.
 
The middle row shows a cocaine addict’s brain after 10 days without any cocaine use at all. What is happening here? [Pause for response.] Less yellow means less normal activity occurring in the brain - even after the cocaine abuser has abstained from the drug for 10 days.
 
The third row shows the same addict’s brain after 100 days without any cocaine. We can see a little more yellow, so there is some improvement - more brain activity - at this point. But the addict’s brain is still not back to a normal level of functioning... more than 3 months later. Scientists are concerned that there may be areas in the brain that never fully recover from drug abuse and addiction.