Thirteen years ago, scientists of the NIH embarked on a journey to do the seemingly impossible: create a map of the human brain. They coined this undertaking the Human Connectome Project (HCP). This crusade is nothing new to the field. Starting with Santiago Ramón y Cajal, who discovered intricate neuronal networks in the late 1800s long before imaging, and for centuries since his time, scientists have been piecing together neuronal networks with the ultimate goal of finding a consistent guide to the human mind. Since its outset in 2009, the HCP has transformed neuroscience research and only plans to grow from here; the scientific community reflects on its purpose, progress, and future.
“The average human brain has 86 billion neurons, forming trillions of connections.”
The average human brain has 86 billion neurons, forming trillions of connections. Neurons send messages down their axons — known as white matter — where connections are formed. These neurons intertwine to ultimately form the most complex and interconnected circuitry known to man. In fact, the cables — or neuronal axons — account for over half of total brain matter. Anatomically, understanding the map of neural connections in the brain, or the connectome, is an integral step toward understanding the fundamental aspects of cognition, systemic brain activity, and functional neuroanatomy.
The HCP contains two branches of research focus: mapping the human brain’s connections in high resolution and creating a new neural imaging scanner that optimizes connectome measurements. To map the human brain in high resolution, the HCP collected data from 1200 healthy adults, specifically the twins and their siblings from 300 families. Data was collected using non-invasive brain scans — task-evoked functional Magnetic Resonance Imaging (tfMRI) — to map the structure and function of the individual brains. The HCP compiled this data to generate a collective map of neural circuitry using overlapping networks within the 1200 scans. Further, they created a scanner that mapped neurons with long-distance axons. These axons reached different and highly specific tissues within the periphery of the human body, allowing the brain to be seen with higher detail and clarity when stimulated.
Being a part of the NIH and highly engaged with their large participant network and the general public, the HCP released the 1200 subjects’ data in 2017. Anyone who has access to the internet also has access to the data library of 1200 different people and the collective structural network. Not only did the HCP transform decades of research, but the project shared it with the public, in turn redefining the open science movement.
Releasing the first round of major data brought not only a surge of knowledge regarding the connectome but a glimpse into the clinical power and applications of connectome data. Scientists broaden their horizons from new research approaches to familiar neurological issues. For example, the Alzheimer’s Disease Connectome Project (ADCP) was launched to develop technology to map Alzheimer’s disease across every stage of its progression. Similarly, the Human Connectome Project for Early Psychosis was launched to collect high-resolution imaging and data on early psychosis patients to share with other researchers. The Lifespan Human Connectome Project in Development was launched to study how common childhood experiences, such as literacy learning, can shape cortex connectivity.
With such intensive and expansive research regarding the human connectome comes newfound excitement — and comfort — in the prospect of having a map that carefully explains emotion, behavior, decision-making, and the human experience. However, this new research brings up an old and persistent question: what does it mean to map the human brain?
“Every person is objectively unique, and this universal difference amongst individuals is reflected in their brains. “
Every person is objectively unique, and this universal difference amongst individuals is reflected in their brains. Moreover, each individual person’s brain is constantly changing and shaping in reaction to their experiences. Thus, many find themselves apprehensive about the idea that one collective map can define a highly individualized and evolving entity. However, the differences in connectivity that define individuality involve much fewer neuronal networks and connections than it would seem. Although people show individual variation in connectivity, much of the connectome responsible for foundational behavior is similar across all people. Thus, a relatively universal connectome can be created and used for investigation into common, yet often poorly understood neurological and psychiatric diseases.
Just like the ever-evolving nature of the human brain, the HCP is far from the end of its journey. The project is not only traveling into a new era of research regarding the connectome, but also a new culture of scientific inquiry and curiosity.