Chronic marijuana users have less brain activation in areas regulating visuospatial memory.
Almost everyone these days has heard some version of the rumor that cannabis is harmful to the brain. For people living through the 1930s, it was a violent, caricatured image of cannabis as the Devil’s Lettuce, making innocent people perform heinous acts of terror and evil. As time passed and generations grew, the image of cannabis as harmful evolved into the equivalent of a fried egg, ruined directly and immediately.
As cannabis doctors, we are reviewing and analyzing research done by a group of Massachusetts researchers to help provide context about whether or not cannabis may be harmful to the brain.
Reviewing the Research
A preliminary NCBI study of functional brain activation among cannabis users explores, more carefully, the ways in which cannabis affects learning and memory, at least in chronic marijuana users, by examining the hippocampus – a region of the brain which controls consolidation of information from short-term memory to long-term memory, and helps to govern spatial memory that enables navigation.
Whether or not someone happens to consume cannabis, the human hippocampus contains a large number of cannabinoid type I (CB1) receptors, which are typically activated by the body’s natural endocannabinoid system.
A number of studies have looked at the effects of cannabis plant products on the visuospatial memory in mice, but such studies in humans are lacking toward a goal of painting a clear understanding of the effects that activation of the natural cannabinoid receptors, either by the body’s innate cannabinoid system or plant-derived molecules, may have on memory.
The researchers in this NCBI study examined hippocampal brain activation in chronic cannabis consumers, compared to non-users. They looked at testing circumstances during which test subjects were asked to perform a visuospatial memory task.
Analyzing the Results
Participants performed a virtual water maze task while an fMRI machine monitored the activation of the hippocampus in the subjects’ brains. This task included two stages, one which included learning the task, and another retrieval stage, during which participants use visual cues that they learned in the task to complete the water maze.
Cannabis consumers performed similarly to non-cannabis subjects, when learning a visuospatial task. However, when tested on their ability to retrieve visuospatial memories, cannabis consumers were not as proficient. Furthermore, cannabis consumers had less brain activation in areas of the hippocampus that control visuospatial memory.
These results suggest that cannabis consumers may be using brain neuron resources in a different way than those who are not using.
Essentially, if both cannabis and non-cannabis consumers are performing with equivalent skill at a given task, yet the areas where visuospatial memory are typically processed seem unchanged between the two different groups, the difference may be explained by considering that other brain regions are being activated in the cannabis consumers.
This theory has been tested over time, in a variety of different modalities, from fMRI to cognitive testing, and the reports of many cannabis consumers harmonizes around the idea that cannabis somehow recruits unusual groups of neurons, at times bestowing the consumer with unusual creativity, a newfound perspective, or unusual clarity or fascination with a subject matter or task.
If it is true, as it seems it may be, that the use of cannabis activates, rather than destroys, brain nerves in unexpected ways, are there reasons to be concerned about potential drawbacks? If other or new nerve systems are firing, are there implications for energy expenditure? Can this new recruitment of neurons be controlled? Is cannabis killing brain cells? Is cannabis bad for the brain? Is cannabis good for the brain?
These are all important, fair questions ahead as we peel away the layers of misinformation and inadequate information in medical cannabis. To read more about the effects of cannabis, explore our CED Blog.