Harnessing the Childhood Brain to Treat Alzheimer Disease, Autism, and Mental Illness

Bret S. Stetka, MD


March 10, 2016

In This Article

Editor's Note:
In his recent Scientific American article, "Critical Ingredients for Brain Development,"[1] Harvard Medical School neurology professor Dr Takao K. Hensch asks his readers, "What's on your music player?," answering, "If you're older than 30 years, it probably includes songs from your teenage years." He then goes on to quote Aristotle: "The habits we form from childhood make no small difference, but rather they make all the difference."

Hensch's piece—as well as his research—explores the potential clinical use of tapping into, or reigniting, the human brain's so-called "critical periods," intervals of neuronal plasticity that occur as we develop and that explain why it's easier to pick up certain tasks and skills during infancy and childhood. Medscape recently spoke with Hensch about his work and about how critical period manipulation could help treat neurologic, psychiatric, and developmental illnesses.

Medscape: To start, how do you define a critical period in the brain?

Dr Hensch: We consider a critical or sensitive period to be a time window when environment is particularly potent in shaping brain function. Essentially, it's a heightened level of plasticity in response to the environment.

Medscape: How long has this concept been around?

Dr Hensch: The term "critical period" was used about 100 years ago initially in response to embryogenesis and susceptibility to chemical insults in early development. There were vulnerable moments when teratogens and other chemicals could affect development. The critical period idea in terms of experience and gene-environment interaction really took off in the mid 1900s with imprinting studies of Konrad Lorenz and Nikolaas Tinbergen, who won the Nobel prize for studying chicks imprinting on their mother figure.

These were behavioral observational studies, and it really became a neurobiological question with the work of Hubel and Wiesel, who were studying the developing visual system and actually started recording changes in brain areas for those functions.

Medscape: It seems that visual system development often serves as a prime example of critical periods in the brain.

Dr Hensch: That's right. Amblyopia or the enduring loss of visual acuity as a result of something as innocuous as a lazy eye—so in the absence of any damage to the retina—leads to a massive rewiring in the visual cortex if it happens early in life but not later in life. There is no cure for amblyopia. It's a bona fide neurodevelopmental disorder, and it has consequences for depth perception but also for quality of life. It was something that could be studied in animals at great detail.

Medscape: This concept explains why it's easier to acquire new skills, such as learning a new language or sport, as a young person. Is that correct?

Dr Hensch: Yes. The idea was adopted by a number of fields, including psychology and linguistics. The anecdotal observations from Aristotle's time onward that it's easier to acquire new skills earlier than later in life started to leverage the idea that circuits in the brain would be plastic to a different degree in different time periods.


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