Cannabis consumers show greater susceptibility to false memories

On occasions, the brain can remember things that never happened. Our memory consists of a malleable process which is created progressively and therefore is subject to distortions or even false memories. These memory "mistakes" are seen more frequently in several neurological and psychiatric disorders, but can also be observed in the healthy population, and become more common as we age. One of the most common false memories we have are of situations from our childhood which we believe to remember because the people around us have explained them to us over and over again. Maintaining an adequate control over the "veracity" of our memories is a complex cognitive task which allows us to have our own sense of reality and also shapes our behaviour, based on past experiences.

In the study published in the journal Molecular Psychiatry, researchers from Sant Pau and Bellvitge compared a group of chronic consumers of cannabis to a healthy control group while they worked on learning a series of words. After a few minutes they were once again shown the original words, together with new words which were either semantically related or unrelated. All participants were asked to identify the words belonging to the original list. Cannabis consumers believed to have already seen the semantically related new words to a higher degree than participants in the control group. By using magnetic resonance imaging, researchers discovered that cannabis consumers showed a lower activation in areas of the brain related to memory procedures and to the general control of cognitive resources.

The study found memory deficiencies despite the fact that participants had stopped consuming cannabis one month before participating in the study. Although they had not consumed the drug in a month, the more the patient had used cannabis throughout their life, the lower the level of activity in the hippocampus, key to storing memories.

The results show that cannabis consumers are more vulnerable to suffering memory distortions, even weeks after not consuming the drug. This suggests that cannabis has a prolonged effect on the brain mechanisms which allow us to differentiate between real and imaginary events. These memory mistakes can cause problems in legal cases, for example, due to the effects the testimonies of witnesses and their victims can have. Nevertheless, from a clinical viewpoint, the results point to the fact that a chronic use of cannabis could worsen problems with age-related memory loss.