Learned Memories and Emotional Memories

The damage drug abuse inflicts on learning and memory is so notable, the Harvard Mental Health Letter labeled addiction a “memory affliction.” It described recovery as “a slow process in which the influence of those memories is diminished.”1 Thus, a basic understanding of memory formation is helpful to understanding addiction.

Scientists believe the brain establishes a new temporary neural network to process new stimuli. Each repetition of the same experience triggers the identical neural firing sequence along identical neural networks, with every duplication strengthening the synaptic links among those networked neurons. Neuroscientists say, “Neurons that fire together wire together.”

If this occurs enough times, a secure neural network is established, as if imprinted, and the brain can reliably access the information over time. A discrete act of learning has been initiated, reinforced, and embedded, a process called “Long-Term Potentiation” (LTP). Most people have experienced this model of learning when memorizing facts and figures or a foreign language’s vocabulary.

Drug use can interfere with LTP. In one experiment (involving rats), for example, morphine disrupted LTP in a key part of the brain’s Limbic system, an effect that continued for about 24 hours thereafter. Dr. Julie Kauer, the lead researcher, explains, “We’ve shown here that morphine makes lasting changes in the brain by blocking a mechanism that’s believed to be the key to memory making. So these findings reinforce the notion that addiction is a form of pathological learning.”2

LTP isn’t the only way to form memories, however. Some experiences are so frightening or pleasurable their neural firing patterns become implanted not with duplication but from a single powerful event. Neuroscientists refer to these as “emotional memories.” A drug high is an example of an emotional memory.3

Emotional memories and those generated by LTP are processed in different brain regions. LTP is the province of the hippocampus. Emotional memories, in contrast, are formed in the amygdala, one of whose primary jobs is to react instantly to danger by triggering the fight-or-flight response. This takes place unconsciously in a few thousandths of a second. Scientists say that addictive drugs give an edge to the amygdala over its counter-balancing frontal cortex, the site of reasoning,4 which intensifies the strength of the emotional memory of the pleasure of drug use at the expense of rational considerations of its negative consequences.5

Researchers have also found that memories are hierarchical. Some are more powerful than others, some are suppressed in favor of others. Efficient recollection of memories involves “pruning” of other less salient ones. Dr. Michael Anderson, a professor of cognitive neuroscience at the University of Oregon, says, “We’ve argued for some time that forgetting is adaptive, that people actively inhibit some memories to facilitate mental focus.”6

In the hierarchy of recollection, emotional memories are easier to recall than those formed through ordinary learning and can override them.  Prioritization occurs almost instantaneously and unconsciously.7

For drug addicts, the emotional memory of the benefits of drugs are so strong and the motivation to repeat the experience so intense, rational memories about the harm caused by drug use are blotted out, explaining why addicts cling to drugs despite ever-worsening consequences.

It’s the overemphasized emotional memory of pleasure and relief from drugs that must be attenuated in treatment and subsequent sobriety. That takes time. A lot of time.

For the next article in the Brain Overview series click here.

To go back to the Addiction Science Menu click here.


1. Memory’s Link to Recovery From Addiction, medicalnewstoday.com, Jan. 10, 2007.
2. Morphine Causes Lasting Changes In The Brain, April 30, 2007; Addictive drugs harm brain’s natural brake, CNN.com, April 26, 2007.
3. An Anti-Addiction Pill? New York Times Magazine, June 25, 2006.
4. The Brain on the Stand, New York Times Magazine, Mar. 1 1,2007
5. Hardest Habit To Break: Memories of the High, New York Times, October 27, 1998.
6. Forgetting May Be Part of the Process of Remembering, New York Times, Jun. 5, 2007.
7. Hardest Habit To Break: Memories of the High, New York Times, October 27, 1998. 


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