Human Memory

By: Eric Hartwell

In the year 1997, an important discovery was made by researchers at Stanford University. They found a cluster of neurons separated by a mere few inches involved in two vital but separate aspects of memory in humans. With the use of a technique known as an MRI (magnetic resonance imaging), it was discovered that people who are attempting to encode information in to the form of a memory use the posterior of the brain’s hippocampus, while more activity was present in the anterior region when the people were attempting to retain information stored in the memory.

As the encoding and retrieving of information is vital to the learning process, this was big news indeed – not to mention the fact that it can also be quite useful, in that the encoding and retrieving process is generally thought to be one of the first to be affected by the onslaught of Alzheimer’s disease in patients.

Thousands of images of the frontal lobe of the brain were captured via the MRI as the individuals participating in the study went about performing different tasks related to memory. The MRI was used to compare flows of blood oxygen to different parts of the brain at different times in order to determine which neurons are more activated during the performing of a specific task. While the MRI cannot show blood flowing to individual nerve cells, it does distinguish activities that can be happening by as little as one or two millimeters apart.

The entire system of memory that they studied was little more than the size of a golf ball. It is an intricate system that is comprised of numerous parts, each of which differs in its composition and the way it is connected to others.

One part of the study involved showing the participants drawings of every day objects and animals one day before as well as thirty minutes before the MRI was launched. Then, during the MRI, the scientists showed the participants words. If they saw the name of something that they had previously been shown before, they were asked to squeeze a bulb. This task involves the retrieval process of memory. During this process, it was later observed in the MRI pictures, there was more brain activity in the subiculum region of the hippocampus when people were showed words for pictures they had seen before.

Another segment of the study involved showing the participants pictures in color of various outdoor and indoor scenes as their brains were being scanned. The indoor pictures would have to be recalled in a later memory test. Some photographs were shown repeatedly, others only once. When the participants were shown photos that they had never seen before, researchers noticed that activity was greatest in a posterior area called the parahippocampal cortex.

While it had long been suspected that different structures in the brain’s memory system were specialized on different tasks, scientists had never before been able to establish this in human subjects – only in laboratory rats and monkeys.

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