Ecstasy tablets. Credit: DEA
Key points:
- Psychedelic drugs can reopen “critical periods” in the brain, but the length of time varies.
- Critical periods have been demonstrated to perform such functions as help birds learn to sing and help humans learn a new language.
- The findings suggest potential to treat a wide range of conditions, such as stoke, deafness, depression, addiction and PTSD.
Neuroscientists have long searched for ways to reopen “critical periods” in the brain, when mammals are more sensitive to signals from their surroundings that can influence periods of brain development. Now, researchers at Johns Hopkins Medicine say a new study in mice shows that psychedelic drugs are linked by their common ability to reopen such critical periods, but differ in the length of time the critical period is open.
“Critical periods” have been shown to perform such functions as helping learn a new language, relearn motor skills after a stroke and establish dominance of one eye over the other eye. But once that period is over, the brain becomes much less open to new learning. Gül Dölen, associate professor of neuroscience, and her team have been researching how psychedelic drugs can reopen the brain during these critical periods. In 2019, for example, her team found that MDMA (also known as ecstasy and molly) opens a critical period in mice.
In the current study, Dölen’s team looked at the reopening potential of five psychedelic drugs—ibogaine, ketamine, LSD, MDMA and psylocibin—all known to enable a sense of discovery about one’s self or the world.
The team trained adult mice to develop an association between an environment linked with social interaction versus another environment connected with being by themselves. Then, they compared time spent in each environment post-drug exposure to see if the critical period opened.
For mice given ketamine, the critical period of social reward learning stayed open for 48 hours. With psilocybin, the open state lasted two weeks. For mice given MDMA, LSD and ibogaine, the critical period remained open for two, three and four weeks, respectively.
The researchers say the length of time that the critical period stayed open in mice seems to roughly parallel the average length of time that people self-report the acute effects of each psychedelic drug.
Next, the scientists looked at the psychedelic drugs’ impact on molecular mechanisms. The researchers found that while LSD and psilocybin use a serotonin receptor as a binding point to open the critical period, MDMA, ibogaine and ketamine do not.
They also found expression differences among 65 protein-producing genes during and after the critical period was opened. About 20% of the genes regulate proteins involved in maintaining or repairing the extracellular matrix—a kind of scaffolding that encases brain cells located in the nucleus accumbens, an area associated with social learning behaviors that are responsive to rewards.