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iPlasticity – rejuvenation of the brain?

iPlasticity – rejuvenation of the brain?

Can the brain of an adult regain the learning capability of a child? The answer seems to be positive. The phenomenon known as iPlasticity, investigated by Eero Castrén from the University of Helsinki, is related to the use of antidepressant drugs, which can help a mature brain regain its “youthful” plasticity.

What is neuroplasticity? In simplest terms, it can be described as the brain’s learning capability. A young brain is very responsive to all kinds of environmental stimuli and learns very fast. This has to do with the organisms’ need to adapt to various conditions – a process which is especially important for more complex species and especially for social mammals, whose social environment, mostly consisting of other individuals, is particularly dynamic and complex. The more unpredictable the organisms’ environment is, the less they can count on their instincts and the more time they need to fully develop mechanisms that are necessary for survival. Human beings are an extreme case, as their social reality is far more complicated than that of any other species, including nonhuman primates, who are our closest cousins.

 

Critical periods

In comparison to most animals, newly born humans can be considered underdeveloped. It takes an unprecedentedly long time for human senses and crucial life skills to fully develop. The key periods in this process are called critical periods, which are characterised by increased brain plasticity. This is when key cognitive functions and skills can be developed. The critical periods come to a close at different stages in life. Some researchers also use the concept of sensitive periods, during which it’s still possible to learn new skills, but the brain plasticity is lower in comparison to critical periods. Thus, even though we learn throughout our lifetime, the experiences of our childhood determine the limits within which further development is possible. It has recently been theorised that the period during which a human being can develop some basic brain structures, cognitive functions, and skills can last from several months to over a dozen years.

Almost everyone has seen a child with an eye-patch. Sometimes, one eye becomes dominant, which makes the second one “lazy”, and, consequently, results in the deterioration of the child’s eyesight. Covering the better seeing eye with an eye-patch aims to compel the weaker eye to make a greater effort, which leads to the stimulation and development of parts of the brain responsible for the eye’s functioning. As neuroplasticity decreases with age, such an intervention is only possible up to a certain moment (see: Maya Vetencourt JF et al., 2008), after which covering the dominant eye no longer leads to the activation of the weaker one.

Fluoxetine – the elixir of neuroplasticity

Until recently, it was thought that due of the decrease in neuroplasticity, it is impossible to stimulate a radical change in the brain leading to the activation of the weaker eye after the critical period during childhood. Yet, the latest research has indicated that some psychoactive substances can temporarily increase neuroplasticity. For instance, it has been quite well documented that psilocybin is capable of restoring openness to new experience typical of young minds, which can be applied in various fields, including psychotherapy, whereas tests on rats have suggested the possibility of reactivation of critical periods with the help of antidepressant drugs, such as fluoxetine. These discoveries have led to the coining of the term iPlasticity, that is, Induction of Juvenile-Like Plasticity in the Adult Brain.

The results of research into fluoxetine’s ability to restore neuroplasticity were presented by Professor Eero Castrén from the University of Helsinki during this year’s Neuronus Forum conference held at the Jagiellonian University in April.

In his studies, Eero Castrén observed that stimulating the weaker eye using the “eyepatch method”  in combination with fluoxetine treatment in adult rats with an underdeveloped eye enables the formation of neural structures needed for the development of vision, as if the rats’ brains returned to the juvenile critical period. According to Castrén, the research also managed to prove that fluoxetine contributes to the improvement of plasticity of amygdala (the part of the brain responsible for a number of processes, including negative emotions), which would explain the drug’s effectiveness in the treatment of trauma (in combination with psychotherapy). This discovery can have important implications for the use of antidepressants, for instance, in cognitive-behavioural therapy, whose main goals include the learning of new patterns of thinking and behaviour. This is due to the fact that as the plasticity of the brain decreases with age, our capability of modifying our attitudes and habits and adopting new ones becomes limited.

Prof. Castrén stresses that fluoxetine itself doesn’t cause any changes in the brain. It only increases its plasticity. Without the eye-patch, the rats that were given the drug did not develop better vision in the weaker eye. Hence, in order to cause changes in the brain, the use of the substance must be combined with the proper mental stimulation, such as certain exercises or therapies.

Original text: www.nauka.uj.edu.pl

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Sources:

Maya Vetencourt JF, Sale A, Viegi A, Baroncelli L, De Pasquale R, O'Leary OF,

Castren E, Maffei L (2008). The antidepressant fluoxetine restores plasticity in the adult visual cortex. Science 320: 385-388.

Castrén E, Rantamäki T (2010). The role of BDNF and its receptors in depression and antidepressant drug action: Reactivation of developmental plasticity. Dev Neurobiol 70: 289-297.

Vetencourt JF, Tiraboschi E, Spolidoro M, Castrén E, Maffei L (2011). Serotonin triggers a transient epigenetic mechanism that reinstates adult visual cortex plasticity in rats. Eur J Neurosci 33: 49-57.

Levi DM. 2005. Perceptual learning in adults with amblyopia: A reevaluation of critical periods in human vision. Developmental Psychobiology 46: 222-232. 

Nelson, Charles. (2000). Neural plasticity and human development: The role of early experience in sculpting memory systems. Developmental Science. 3. 115 - 136. 10.1111/1467-7687.00104.

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