Drinking heavily as an adolescent can do long-lasting damage to the area of the brain that controls learning and memory, according to new research from Duke Medicine.
The study, published in the journal Alcoholism: Clinical & Experimental Research, examined how exposure to alcohol during adolescence can affect the growth of a brain that has yet to develop fully, leading to abnormalities that can influence behavior in adulthood.
“In the eyes of the law, once people reach the age of 18, they are considered adult, but the brain continues to mature and refine all the way into the mid-20s,” lead author Dr. Mary-Louise Risher, a postdoctoral researcher in the Department of Psychiatry and Behavioral Sciences at Duke, said in a statement.
While adolescence is a crucial period in terms of cognitive, emotional and social maturation, it also happens to be a time when alcohol consumption frequently begins and continues at high levels.
“It’s important for young people to know that when they drink heavily during this period of development, there could be changes occurring that have a lasting impact on memory and other cognitive functions,” said Dr. Risher.
Although it is widely acknowledged that adolescents are more vulnerable than adults to the effects of alcohol consumption on learning and motor functioning, the long-term consequences of repeated alcohol exposure in adolescence have yet to be thoroughly examined, said Dr. Risher.
For the study, the researchers periodically exposed young rats to levels of alcohol during their adolescence that would lead to impairment but not sedation in humans for a period of 16 days. Following this, the rats received no further alcohol, allowing them to mature into adulthood over 24-29 days.
Previously, the researchers had demonstrated that animals exposed to alcohol during adolescence would grow up to be less adept at memory tasks than animals that were not exposed to alcohol. However, they did not know how the hippocampus, the region of the brain associated with memory and learning, was affected.
Hyperactive LTP and seemingly immature dendritic spines
In the new study, the researchers measured a cellular mechanism known as long-term potentiation (LTP) in the hippocampus. LTP is the mechanism by which the brain synapses strengthen as they are repeatedly used to learn new things or recollect memories.
Vigorous synaptic activity is best for efficient learning and, as a result, LTP is typically highest in younger people who have to acquire large amounts of new memory when approaching adulthood.
The researchers predicted they would find lower levels of LTP in the adult rats who had been exposed to alcohol during adolescence. However, what they found was the complete opposite.
Senior author Dr. Scott Swartzwelder, a professor of Psychiatry and Behavioral Sciences at Duke and Senior Research Career Scientist at the Durham VA Medical Center, explains the finding:
“At first blush, you would think the animals would be smarter. But that’s the opposite of what we found. And it actually does make sense, because if you produce too much LTP in one of these circuits, there is a period of time where you can’t produce any more.”
Consequently, an animal producing too much LTP will eventually stop learning. “For learning to be efficient, your brain needs a delicate balance of excitation and inhibition – too much in either direction and the circuits do not work optimally,” said Dr. Swartzwelder.
A structural change in the nerve cells of the hippocampus was observed alongside the hyperactive LTP. The dendritic spines, vital for cell-to-cell communication, appeared lanky and spindly, as though they were immature. Mature spines are shorter and look similar to mushrooms.
“Something happens during adolescent alcohol exposure that changes the way the hippocampus and other regions of the brain function and how the cells actually look – both the LTP and the dendritic spines have an immature appearance in adulthood,” explains Dr. Swartzwelder.
According to Dr. Risher, the immature quality of these brain cells could be associated with behavioral immaturity. “It’s quite possible that alcohol disrupts the maturation process, which can affect these cognitive function later on,” she adds. “That’s something we are eager to explore in ongoing studies.”
These findings add to a growing body of research linking exposure to alcohol during adolescence with permanent changes in brain structure and functioning.
In a study published earlier this month, researchers found that alcohol may disrupt gene expression, contributing to abnormalities in brain development and behavioral changes in adulthood. After analyzing the brain tissue of rats who had been given alcohol when they were young, the researchers discovered DNA abnormalities in the amygdala, a small brain region associated with decision-making, emotional reactions and memory. These changes were linked with a significantly increased risk of anxiety and alcohol use disorders in later life.
In a similar study published in November, researchers found that binge-drinking during adolescence can trigger myelin deficits in the brain’s prefrontal cortex, which may result in permanent problems such as impulsivity, memory loss, and poorer cognitive functioning.