Posts Tagged ‘cognitive enhancement’

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Keeping the brain plastic

Wednesday, 31 March, 2010

Neural plasticity, the capacity for neurons to change their connections, is a fundamental property of the brain. It’s what allows us to learn. But as we age, the plasticity of the brain decreases. Indeed, there are developmental windows called ‘critical periods’ where the brain is especially plastic, usually when very young. The neural basis for vision, as an example, is laid down at during infancy, and doesn’t change easily thereafter. This is why kittens, raised in a visual environment of many vertical stripes, find it difficult as adult cats to see horizontal stripes – their brains, while plastic, had adapted for certain visual features, and found it difficult to adapt to new ones.

Recently, researchers at the University of California San Francisco have found a way to renew the infant-like plasticity of the mouse brain, allowing childlike learning to begin again. They did this by injecting embryonic mouse neurons (not to be confused with embryonic stem cells) into young mice, which had been raised with one eye deprived of light. Without the injection, mice that were deprived up until around a month old (the usual critical period for mouse ocular dominance) would have difficulty adapting to seeing through the eye that had been deprived of light. But with an injection of embryonic neurons into the brain, the mice went through sort of a second critical period, when the injected brain cells were about a month old, thereby aiding the mice to learn to see from their deprived eye.

This has profound consequences for enhancement of human intelligence. The obvious therapeutic outcome would be using embryonic human neurons, taken from human embryos or cultured from human embryonic stem cells, and injecting these into adult humans to give a second chance at a critical period of learning, which would be useful for re-learning to walk after an injury or learning to adapt to blindness (or, I don’t know…learning to control your new cyborg limbs?). But on a grander scale, if we could have a constant trickle of neural stem cells, developing into immature neurons, throughout life, we could very well keep our critical periods going for the rest of our lives, allowing our brains to stay young and malleable!

There is one caveat I can think of. There must be a reason why the brain has evolved to shut off critical periods of learning. Most likely, learning is a costly process in some way, thereby creating a pressure to keep learning periods are short as possible.  If this is merely an increased energy cost, humans in the first world can probably deal with it (seeing as most of us eat too much food energy anyway). But if shutting down mechanisms of learning is necessary for enhancing the function of the newly learned circuits (that is, if we don’t perform as well if we keep ‘changing our minds’), there may be a question of whether learning is worth the cost.

I would assume in this ever changing technological environment and with our lives getting longer and longer (making what we learned during our critical period more and more irrelevant), that keeping the brain plastic would be very useful indeed.

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Enhancing memory and learning in mice

Monday, 23 March, 2009

Recently, a review article by Yong‑Seok Lee and Alcino J. Silva was published in Nature Reviews Neuroscience, with the title ‘The molecular and cellular biology of enhanced cognition‘. If you are lucky enough to have a subscription, or know a library that can get this journal article for you, do.

The review lists 33 genetic modifications that lead to some level of enhanced memory and learning in mice. It also discuses the general methods by which these modifications work, focussing on enhancement of a form of neuronal plasticity known as long-term potentiation. NMDA receptors, the role of calcium as a messenger and the various enzymes and transcription factors that are recruited to create the cellular basis of a memory. The review also discusses other mechanisms, like epigenetics, growth factors, the involvement of glia, and also presynaptic signalling. Finally, the review looks at caveats in the current research in cognitive enhancement.

The authors also make a nod in the direction of bioethics, saying:

[I]t is also important to stress that memory enhancing manipulations raise a number of ethical issues that are outside of the scope of this Review, but that merit careful consideration and discussion170,171.

For interests sake, references 170 and 171 are:

170: Rose, S. P. ‘Smart drugs’: do they work? Are they ethical? Will they be legal? Nature Rev. Neurosci. 3, 975–979 (2002).
171. Farah, M. J. et al. Neurocognitive enhancement: what can we do and what should we do? Nature Rev. Neurosci. 5, 421–425 (2004).