To fear or not to fear: It may depend on how old you are

ninocare, pixabay.com, CC0 1.0
ninocare, pixabay.com, CC0 1.0

For many children and teenagers, life is a far cry from the happy memories filled with ice cream trucks and baseball games of my own American youth. First-hand exposure to extreme violence, sexual abuse, natural disasters, poverty, or life-threatening illness can instill terror into a person – at any age, in any part of the world.

Under normal circumstances, fear-learning is a highly adaptive, evolutionarily conserved process that allows one to respond appropriately to cues associated with danger, thus increasing chances for survival. In the case of psychiatric disorders, however, fear may persist long after an environmental threat has passed. This unremitting and often debilitating form of fear is a core component of many anxiety disorders, including post-traumatic stress disorder (PTSD), and often involves exaggerated and inappropriate fear responses, as well as a lack of reappraisal once a previously threatening stimulus becomes safe.

“Lack of knowledge about the dynamic development of the brain’s fear processing centers may prohibit similarly successful treatment outcomes in children and adolescents.”

While advances in psychiatry and neuroscience have shed remarkable light on how brain activity is altered in fear-related disorders, the vast majority of research has exploited the fine-tuned adult brain. As such, various pharmacological and behavioral therapies used for the treatment of PTSD often have their roots in a physiologically mature neural framework.

While existing therapies and medications offer significant benefit to adult patients, a comparative lack of knowledge about the dynamic development of the brain’s fear processing centers may prohibit similarly successful treatment outcomes in children and adolescents.

In an effort to help inform this vulnerable population, a handful of neuroscientists and psychologists have embarked on a quest to better understand the developing brain as it relates to fear plasticity. By performing parallel rodent and human experiments, my colleagues and I found that circuits within the brain involved in the processing of fearful situations change across development. We have shown that after fears are acquired, the process of re-learning to adapt once a threat has passed is also highly influenced by age.

Interestingly, the adolescent brain appears particularly resistant to making the connection that something once predictive of threat can subsequently become safe. The specific connectivity patterns between certain brain regions at this age may lead adolescents to remain fearful long after a threat has passed – much longer than their older or younger counterparts.

“The adolescent brain appears particularly resistant to making the connection that something once predictive of threat can subsequently become safe.”

The most validated treatment for PTSD involves exposure therapy, which is based on learning principles. Through repetition and exposure, this therapy involves the successful reassessment of a previously threatening stimulus as no longer dangerous. The diminished ability to extinguish typical fear memories during adolescence may have a large clinical significance in regards to these treatment approaches.

New research suggests that adolescents may have enhanced capacity for certain types of learning, such as environmental or contextual learning. Approaches designed to tap into other brain regions important for fear processing, such as those involved in sensing environmental cues, may prove useful in helping this age group reassess when a prior threat is no longer dangerous.

Non-linear neural development

Through molecular neuroscience approaches, we injected fluorescent dyes into precise brain regions of laboratory mice at specific developmental ages. By following the fluorescent patterns under a microscope, we found that certain regions of the fear circuit are connected very tightly at early ages, but that these connections are pruned back during adolescent ages, only to re-form tightly again during adulthood. As these connections become stronger, emotional memories once thought to be absent can sometimes emerge.

While many aspects of development, such as growing taller, progress in a unidirectional manner, our recent findings suggest that development of fear-circuitry is a non-linear process. Rather, an intricate reciprocal balance exists within the brain. Essentially, neural development in one region may lead to alterations in connectivity or activity in another brain region. These connections can tighten and weaken across the lifespan and can also be influenced by exposure to stress early in life.

This domino effect can alter not only specific brain activity patterns, but also change one’s resulting emotions and behavior. Understanding the strength of these connections between different brain regions may ultimately help inform what learning techniques are most, or least effective, at specific ages.

“Understanding the strength of these connections between different brain regions may ultimately help inform what learning techniques are most, or least effective, at specific ages.”

Why does age matter? One’s ability to respond to certain types of cognitive-behavioral therapy likely changes across the lifespan. We already know this phenomenon when it comes to standard prescription medication. A toddler cannot routinely swallow pills – nor would his doctor expect him to, so both dosage and means of delivery are targeted specifically for that stage of his life. The cherry-flavored syrup given to me on a spoon when I was a child had a specific dosage and means of delivery and so too should certain treatments for particular psychiatric disorders.

For children and teenagers living in inner-city communities, war torn countries, weather-ravaged towns, or victimized areas, the effects on their subsequent mental health can be persistent and pervasive. So how should one effectively treat trauma-exposed children and teenagers with paradigms designed for adults? What about kids who might have adapted to a negative situation or environment – will they remain healthy as adults?

These questions are central to the health and well being of children across the globe and as such, will require a deeper understanding of both normative an abnormal neurodevelopment.

“Emotional learning, stress, and development: An ever-changing landscape shaped by early-life experience.” 2017 Apr 27. pii: S1074-7427(17)30064-3. doi: 10.1016/j.nlm.2017.04.014.