What Does Tu B’Shevat Have to do With the Brain?

Today is Tu B’Shevat, which is the day in the Jewish calendar that is dedicated to celebrating the trees, plants, and other agriculture. We can use this day to marvel at the wonders of the gifts of nature – the fact that we can place a small hard seed in the ground, and it becomes a fruit-bearing tree. That is nothing short of miraculous.

Hello everyone. This is my debut blog post on The Times of Israel. In the following paragraphs, I will introduce myself, what I write about, and share with you a message about your brain on this Tu B’Shevat.

I am an American-born neurologist living in Modiin. My passion is talking to people about how the brain works, and in particular, how the brain is related to the real things that people think about and the way we act. Besides diagnosing and treating disease, a large part of my job is to explain to people about the brain and how it relates to their problem. Essentially, a doctor is a teacher. They don’t tell you that in medical school, but we probably best help people by giving them the peace-of-mind of understanding more than they did before.

In this blog series, I intend to discuss topics of general interest, related to neurology, psychology, and thinking. There is a lot of material on the Internet, but very little is accessible to regular people (without a science degree). My goal is to provide some interesting information and provocative ideas. In short, these pieces may get you to think a little differently than you did before.

So, a little thought about Tu B’Shevat and the brain, adapted from Embracing the Unknown: A Fresh Look at Nature and Science (published by the author in 2017).

Cells in the brain are treelike

For man is (like) a tree in the field (Deuteronomy 20:19)

The brain is densely packed with approximately 100 billion nerve cells. Each cell has between 1,000-5,000 connections to other cells. That amounts to around 500 trillion connections – and those connections are where the business of information processing takes place. You may be shaking your head. How could we possibly know what is going on, if there are so many cells? First, a little history.

Santiago Ramón y Cajal is considered the father of modern neuroscience. Born in 1852 in Spain, Cajal was a physician, scientist, and avid artist. His application of a novel tissue-staining technique, invented by the Italian scientist Camillo Golgi, to brain tissue resulted in definitive evidence that the brain is composed of individual cells that contact each other.

This discovery, known as the “neuron doctrine,” formed the basis for all further research into the function of the brain. Cajal went on to study the different structures of cells from different areas of the brain. Quickly it became clear that the brain is not homogeneous and is rather comprised of a complex variety of cell types. The long projections from the neuronal cell body look like branches on a tree, and the branching patterns could be quite intricate. Later scientists analyzed the branching of neurons using better techniques and found that these branches divide into more branches and so on; the level of complexity of the branching architecture was the same at the large scale and the smaller scales.

When the degree of complexity is comparable at multiple scales, it is known as “fractal,” a property that occurs frequently in other areas of nature. The drawing below, for example, shows a tree with each branch dividing into two other branches; that level of complexity is consistent from the trunk all the way to the most distant branches. In nature, the complexity of the neuronal tree is not a matter of random growth patterns but a programmed feature of the cell’s structure.

The same complex branching is true for trees in the forest. This remarkable feature deserves a little more attention. When people build things, we try to keep it as simple as possible. The tallest man-made structures are buildings, towers, and radio antennas – all built singular column, where the base is most complex and the tops are simple. Trees, on the other hand, have branching patterns that go from the base to the top. So, trees are able to spread out their leaves to capture as much sunlight as possible, and that is needed for them to produce energy for its growth and maintenance. It is also critical for the tree to produce oxygen for us to breathe. This whole mechanism – provided for free by nature – is so wondrous, that no human invention comes close.

We can now better appreciate the incredible complexity of the brain. The nerve cells process information by combining signals from connections all along their branches. Neuroscientists like Professor Idan Segev at Hebrew University construct computer simulations of neurons to better understand how they process information, but even today’s sophisticated models do not capture the complexity of the real brain. On this Tu B’Shevat, let us reflect on the wonders of nature … It is OK to get emotional and feel the awe.