There has been studies done using animal specimens as well as many humans where substantial evidence through research indicates that marijuana exposure during development can cause long-term or possibly permanent adverse changes in the brain. Specimens exposed to THC before birth, soon after birth, or during adolescence show notable problems with specific learning and memory tasks later in life. Cognitive impairments in adult animal specimens exposed to THC during adolescence are associated with structural and functional changes in the hippocampus. The studies in animal specimens also show that with exposure to THC there is an altered reward system, increasing the likelihood that the specimen would self-administer other drugs given the opportunity. Imaging studies in human adolescents show that regular marijuana users display impaired neural connectivity in specific brain regions involved in a broad range of executive functions like memory, learning, and impulse control compared to non-users.
The ability to draw definitive conclusions about marijuana’s long-term impact on the human brain from past studies is often limited by the fact that study participants use multiple substances, and there is often limited data about the participants’ health or mental functioning prior to the study. Over the next decade, the National Institutes of Health is planning to fund a major longitudinal study that will track a large sample of young Americans from late childhood (before first use of drugs) to early adulthood. The study will use neuroimaging and other advanced tools to clarify precisely how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development.
Memory impairment from marijuana use occurs because THC alters how information is processed in the hippocampus, a brain area responsible for memory formation.
Most of the evidence supporting this assertion comes from animal studies. For example, animal specimens exposed to THC in utero, soon after birth, or during adolescence, show notable problems with specific learning/memory tasks later in life. Moreover, cognitive impairment in adult rats is associated with structural and functional changes in the hippocampus from THC exposure during adolescence.
As people age, they lose neurons in the hippocampus, which decreases their ability to learn new information. Chronic THC exposure may hasten age related loss of hippocampal neurons. In one study,animal specimens exposed to THC every day for 8 months (approximately 30 percent of their life-span) showed a level of nerve cell loss (at 11 to 12 months of age) that equaled that of unexposed animals twice their age.
Adapted for Footprints of Serenity from Drugabuse.org