Re-opening Windows: Manipulating Critical Periods for Brain Development

Abstract

The brain acquires certain skills-from visual perception to language-during critical windows, specific times in early life when the brain is actively shaped by environmental input. Scientists like Takao K. Hensch are now discovering pathways in animal models through which these windows might be re-opened in adults, thus re-awakening a brain's youth-like plasticity. Such research has implications for brain injury repair, sensory recovery, and neurodevelopmental disorder treatment. In addition, what we know today about these critical windows of development already has enormous implications for social and educational policy.

Fig 1:

Windows of Plasticity in Brain Development Windows of heightened plasticity in brain development are called critical or sensitive periods. In humans, there are sensitive periods for the development of sensory pathways (vision, hearing), language, and higher cognitive function, as well as many other brain functions. Note that the peak of plasticity for each sensitive period is staggered throughout development., ,

Fig 2:

Consequences of manipulating critical period plasticity The developing brain exhibits higher plasticity than the adult brain. During normal development, critical periods occur in a predictable temporal sequence, as depicted here with examples of vision, language, and higher cognitive function.

1. Following genetic disruption or pharmacological manipulation, certain critical periods may be accelerated or delayed. Critical periods might then become incorrectly synchronized or uncoupled from one another across the brain. Alternatively, the extended duration of one critical period may stall the onset of others. Interventions that restore the expected hierarchical progression of critical periods during brain development may then be useful in preempting mental illness.

2. In cases of stroke or other brain injuries suffered during adulthood, the main obstacle to treatment is believed to be the limited plasticity of the adult brain. Thus, a tantalizing treatment strategy would be to rekindle critical period plasticity in the damaged circuits.

3. The ability to tap into critical period plasticity during adulthood, likely through non-invasive means (such as incremental training, enriched environments, or educational video games), could also enhance the potential for lifelong learning.

Fig 3:

Factors that affect critical period timing Diverse experimental manipulations—ranging from biochemical, genetic, and surgical interventions to environmental changes or electrical stimulation—are known to induce juvenile-like plasticity in the adult visual cortex. These manipulations are all thought to trigger plasticity via a common circuit mechanism: adjusting the balance of excitation/inhibition (E/I balance) in the brain.