In this blog post, we will examine how the connectome, the network of connections between 860 billion neurons, shapes our thoughts and emotions.
Our bodies are made up of cells. There are approximately 37.2 trillion cells in our bodies, and about 86 billion of them make up the brain. These brain cells are called neurons. A single neuron is divided into three main parts: dendrites, cell bodies, and axons. Dendrites receive electrical signals from other neurons, the cell body is the central part of the cell, and the axon transmits electrical signals received from the dendrites to other neurons. At the point where two neurons meet, there is a structure called a synapse. For example, when the axon of neuron A meets the dendrite of neuron B, there is a gap called a synapse between them. The electrical signal is converted into a neurotransmitter at the end of the axon of neuron A, spreads across the synapse gap, and reaches the dendrite of neuron B, where it is converted back into an electrical signal. A single neuron is connected to numerous other neurons. The dendrites of neuron A are connected to millions of axons, and the axon of neuron A is connected to an equal number of dendrites. For a specific neuron to activate, the voltage must exceed a certain threshold value. If the total sum of electrical signals received from multiple other neurons exceeds this threshold value, the neuron activates.
Conversely, if the voltage is even slightly insufficient, the neuron cannot transmit any electrical signals to the next neurons. Connectionism or Connectome Theory is a theory in cognitive science that all mental activities (thoughts, emotions, etc.) can be explained through the connectome. So what is the connectome?
You may have heard the term “genome.” A genome refers to the entire set of genes in an organism, and it determines that organism’s appearance, metabolic activities, and many other characteristics. For example, analyzing a person’s genome can reveal their likelihood of developing Alzheimer’s disease. If the genome represents the entirety of genes, the connectome represents the entirety of connections between neurons. In the distant future, when technology advances sufficiently, we may be able to uncover how all 86 billion neurons in the human brain are interconnected. According to the theory of connectivism, at that point, we may be able to read a person’s mind through their connectome.
Currently, the methods for studying the connectome are very limited. To put it simply, a small portion of the brain is removed and sliced into very thin layers. These layers are then analyzed one by one under a microscope, and the images are input into a computer. The computer then analyzes and synthesizes these numerous two-dimensional images to create a three-dimensional image. Therefore, when studying the connectome, we can only use brains that have already died. Non-invasive scanning technologies such as fMRI are not sophisticated enough to distinguish individual neurons and can only tell us roughly which parts of the brain respond to a given stimulus.
So, what is the significance of analyzing a dead brain? To understand this, we must recognize the two aspects of the brain and mind. The first aspect of the brain and mind is evident in our daily lives. We think about various things throughout the day, such as needing to do the dishes. We also enjoy watching a TV variety show while admiring a beautiful landscape, and we can get angry and then quickly become happy. At that moment, the paths and patterns of electrical signals flowing through our neurons are constantly changing. It is like a flowing river. However, for a river to flow, there must be a riverbed. This riverbed is the connectome. Compared to the speed of the flowing water, the shape of the riverbed is relatively constant. Similarly, the connectome is relatively constant compared to the rapidly changing electrical signals. Even though our emotions may be fickle, everyone has their own unique personality. Such personalities are formed by each person’s connectome. Additionally, characteristics that do not change easily over time (such as childhood memories) are all rooted in the connectome, which is like the riverbed. However, this does not mean that the connectome remains the same forever. Just as the riverbed erodes and changes shape as the river flows, our connectome also changes. As we study our respective fields, watch entertainment programs, and get angry, the electrical signals flowing through our neurons gradually alter the shape of our connectome. In other words, the flow of electrical signals and the connectome interact with each other. This is where the connectome differs significantly from the genome. The genome remains unchanged from the moment of conception until the end of an individual’s life. However, the connectome changes based on experience and is therefore not as deterministic as the genome. Since the connectome encompasses both nature and nurture, it is more advantageous than the genome in explaining human beings. This is why the core hypothesis of connectivism, “You are your connectome,” has emerged.
