This is the 2007 version. Click here for the 2017 chapter 06 table of contents.

Chemical Modulation of Memory

McGaugh (2000) summarized four decades of research showing that chemicals in the nervous system influence memory. In particular, low doses of adrenaline secreted within the nervous system very soon after learning (within about 30 seconds) seem to encourage memory formation. This process by which memories are strengthened over time, following an experience, is called consolidation. McGaugh points out that the brain does not "need" consolidation, because some forms of memory are extremely fast. Consolidation probably evolved because it gives emotions a chance to have an impact on memory formation. Consolidation helps to insure that events that are more important to the organism over a sustained period of time are better remembered.

What is memory consolidation?
Why is it useful for the brain?

What level of adrenaline is helpful to memory?
What is the "obvious explanation"?

How do opiate transmitters affect memory?

Adrenaline helps memory, but only in small doses. Larger doses of adrenaline actually hurt memory. This is shown by McGaugh's studies, too. If a rat receives a large dose of adrenaline, the rat's memory performance worsens.

McGaugh noted that the effects of adrenaline are very strong. They are also very widespread in the animal kingdom. The obvious explanation is that events which alert an animal (such as the presence of danger or opportunity) are also the events worth remembering, so this is an easy way for the brain to select important memories.

Opiate transmitters like the endorphins have an effect opposite to adrenaline. They reduce the likelihood animals will remember an event (Cicala, Azorlosa, Estall, & Grant, 1990). To have this effect, they must be injected immediately after training. Could this be the cause of the anterograde amnesia that affected the football player, described on the previous page? Surely endorphins would be released after a big "hit," since endorphins are usually released whenever a person is injured or under a great deal of stress. This might interfere with memory formation in such a situation, producing anterograde amnesia.


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