By: Katie Davis

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Here in the Dunn Lab, a lot of our research is focused on identifying sensitive periods in development, or age stages in the course of the lifespan when the brain is highly plastic, and thus when experience—such as exposure to adversity—may be particularly impactful.  As a lab, we’re especially interested in identifying when sensitive periods occur that shape risk for depression.  By understanding when stressful experiences have the greatest effect on our mental health, we can begin to design interventions that are timed to be most effective in preventing depression.

It’s important to remember though that sensitive periods aren’t just periods of high risk, when adverse experiences are more harmful.  They’re also periods of high reward, when enriching experiences—like exercise or other health-promoting interventions—can have long-term benefits for wellbeing. 

Moreover, sensitive periods aren’t just involved in shaping mental health. In fact, some of the earliest work on sensitive periods came from of studies examining the effects of our life experiences on all kinds of outcomes.

Ever wonder what sensitive periods in development you may have experienced? Here are five sensitive periods you likely never knew existed:

  1. Sensitive period for word sounds. Have you ever noticed that non-native English speakers sometimes have difficulty distinguishing between certain consonant sounds, like l and r? Or perhaps you’ve tried to learn Hindi, but struggled with the difference between Da and da? If so, you’re noticing the effects of a sensitive period for word sounds.  Before 10 months of age, infants can universally hear the difference between different word sounds, or phonemes.  However, if a baby doesn’t hear a particular word sound spoken by the people in its surroundings, it will lose the ability to detect that phoneme by 10-12 months of age.  

  2. Sensitive period for second language learning.  Relatedly, you’ve probably heard at some point that younger children have an easier time learning a second language.  A recent study out of MIT suggests that this is true—sort of.  Researchers found that the sensitive period for learning a second language’s grammar appears to last much longer than previously thought, up to age 17 or 18. However, in order to learn to speak as well as a native speaker, children generally need to start learning the language by age 10.

  3. Sensitive period for food acceptance.  How’s your taste for seal blubber?  If that doesn’t sound too appealing, it may be that blubber has a texture you didn’t encounter during your first year of life.  In fact, there’s evidence for sensitive periods for both complex flavors and textures during infancy.  Taste exposures between 4 and 6 months seem to be particularly important for later acceptance of certain flavors, although learning to like new flavors can occur at any age with repeated exposures (so keep trying out those more adventurous foods!). 

  4. Sensitive period for musical ability.  Whether or not you hated those early piano lessons, they were probably changing your brain.  Comparisons between highly skilled musicians have found that musicians who began their training before age 7 performed better on tasks designed to test the kinds of motor synchronization required in musical performance auditory and visual sensorimotor synchronization tasks than those who began their training after age 7.  Moreover, these earlier-trained musicians had greater connectivity in the white-matter structure of their auditory and motor regions, even after accounting for total years of training and experience.

  5. Sensitive period for vision. Some of the earliest and most in-depth work on sensitive periods has focused on age windows when exposure to visual input is particularly important for the development of typical sight.  There appear to actually be several different sensitive periods for different aspects of vision.  For example, children who are deprived of visual stimulation starting at 6 months of age are likely to go on to experience serious difficulties with visual acuity, but might not have any problems detecting the direction of motion.  Furthermore, research in animal models suggests that whether you experience a particular sensitive period, when it starts, and how long it lasts might all be regulated by certain genes.  In other words, our sensitive periods might themselves be sensitive to our genetics!

So remember, sensitive periods aren’t the whole story; in most domains, learning can continue across the life course.  But by understanding when sensitive periods occur, we can determine when to optimally time exposures—whether those are flute lessons, new foods, or, in the case of our work, mental health interventions—to have the biggest impact on the health and development of our brains.

 
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