Our brain: so powerful, yet so little understood
Imagine planet Earth on a clear day, 120 million years ago. The majestic Tyrannosaurus rex, with the length of a bus, weighing the equivalent of two adult elephants and as tall as a two-story house, walks around menacingly. Then, just 10,000 years ago another species, less than 7 feet tall and weighing less than 300 pounds, made its earthly appearance.
Today, the once powerful T. rex and all other giant dinosaurs are extinct; the fragile less-than 7-foot humans survived. The human brain, twice the weight of a T. rex’s brain (which means higher brain to body ratio) made all the difference.
The human brain made possible discoveries, accumulation and propagation of knowledge. By developing abstract thinking, language systems and complex calculations, the human brain has built 2,000-foot tall buildings, has flown 747 airplanes, heavy as 34 elephants altogether, sent humans to the moon and calculated when and how the universe began.
Misconceptions and even plain ignorance, however, still hover over this amazing organ called “the crown jewel of the human body.” A common and widespread belief is that as people get older, the brain loses its learning abilities.
This article emphasizes that the understanding of brain physiology, meaning its functioning, can be applied to improve the quality of life of aging people. Is not old age per se that is the cause of diminished brain function, it is the lack of use.
The brain (blue in Figure 1, top) is the most complex organ of the human body. Therefore, it will be useful to review its structure and organization.
A neuron, basic unit of the brain, is composed of three elements: the cell body, the dendrite (a short and highly branched end) and the axon, a long end without branches (Figure 1, middle). Axons are insulated by a sheath of fatty material called myelin and typically bundle forming nerves. Glia cells such as astrocytes and oligodendrocytes play a supporting role.
So, how do these pieces work together? Any stimulus received, for example, by the senses — eyes, ears, nose, touch, etc. — is transduced into an electric signal that, in milliseconds, travels from cell to cell.
The connecting point of a neuron’s axon with the dendrite of another is called synapse; at this location a chemical substance, the neurotransmitter, is released, which facilitates signal transmission (Figure 1, bottom). Some 100 billion neurons — a number that approximates the number of stars in our galaxy — are wired thorough trillions of synapses.
Why is that older people have more difficulty learning? Does age change any of these structures?
Recently, Stanford University professor Carla Shatz referred to a puzzling fact we all have faced at some point. “It’s difficult to learn how to speak French without an accent during adulthood, but we can learn many different languages and speak them perfectly if we learn them during childhood,” wrote Shatz, winner of the Neuroscience Kavli Prize — Nobel equivalent.
In the process of learning specific skills, connections are established among neurons, involving many synapses but if these circuits are not used, they are eliminated. (Figure 2 explains the underlying mechanism in a simplified manner. )
Two pre-synaptic neurons, meaning located before the synapses, feature one synapse each; one is constantly used, it is functional (highlighted yellow in the figure), but the other is less active. Those synapses connect to the post-synaptic neuron.
When a synapse is less active or not used, a signal is triggered and it is destroyed. “Synaptic pruning” takes place. So, it is inactivity that causes reduced learning ability. If synapses were kept active, learning ability would’ve lasted a lifetime.
Indeed, recent neuroscience discoveries support evidences that putting the brain to work preserves and increases learning capabilities. Neurogenesis and epigenetics, genetics and neuroplasticity are mechanisms activated when the brain engages in learning.
For example, post-birth neurogenesis — formation of new neurons after birth — does take place, a fact unknown to neuroscientists until 1962. [Previously, they believed that humans were limited to carrying a specific number of neurons for life].
Epigenetics, the interaction with the environment — the life experience that is different in every individual — as well as genetics that determine the genes that are important for brain function and neuroplasticity that allows the brain to establish new wiring among neurons, i.e., new synapses are generated.
And speaking of brain usage, a commentary titled “Why Einstein was a genius” appeared on the journal Science based on the detailed analysis of the brain of the famous man. Michael Balter, the commentator, emphasized that although the weight of Einstein’s brain was unexceptional, the shape was markedly different, compared with 85 other brains previously studied.
It’s known now that Einstein’s brain was more convoluted, with different shapes of lobes (regions), i.e., frontal, parietal (lateral) and occipital (lower-back area of the cranium), as well as having a greater density of neurons and glia cells. Balter reminds us that scientists have correlated such differences with Einstein’s extraordinary ability to deal with abstract ideas and “planning, focused attention and perseverance in the face of challenge.”
So, was the great man born with this exceptional brain or was it programmed to be exceptional? Was genetics or systematic training responsible for the differences in shape that yielded high intelligence?
Balter mentions that Dean Falk (Florida State University) and co-authors agree with the idea that both nature and nurture were probably involved. (Nature and nurture refer to the influence of hereditary factors and brain usage, respectively.)
“Since Einstein’s parents were ‘very nurturing,’ [according to Falk,] they encouraged him to be creative and independent not only in science but also in music, paying piano and violin lessons,” Belter commented. “Einstein programmed his own brain, he had the right brain in the right place at the right time to make great discoveries,” according to Falk.
In conclusion, learning specific skills depends on billions of neurons and trillions of synapses that have to be wired specifically for that purpose. Recent advances in neurosciences, specifically, neurogenesis, epigenetics and neuroplasticity, confirm that such specific wiring is kept and perfected by usage.
Lifetime learning is possible provided that the brain is constantly challenged. Reduced learning capability is the price for not using it.
“Use it or lose it” is what matters, not aging.
(Contact the author of this article, Jesus Zaldivar, associate-editor of The Commuter: firstname.lastname@example.org)