Sometimes I feel like there’s something almost absurdly circular about what we neuroscientists do for a living—using our brains to try to understand the brain. It’s like if a cardiologist’s heartbeat could drum out his patient’s diagnosis in morse code, or if a urologist could pee out the medicine for treating her patient.

In my previous post I talked about what makes the brain so cool. To me, it boils down to the fact that all of our thoughts, perception, actions, and emotions are generated by physical processes occurring within our brains. Your entire lifetime of memories is stored in that small space inside your skull.

How can we possibly hope to understand how this works?

cartoon of a neuron (credit: gfinder)

The thing is, we actually understand the basics of most of those physical processes of the brain. We know that the fundamental unit of the brain is the neuron, a brain cell that produces electrical signals and communicates with other neurons. We understand how those electrical signals, called action potentials, are generated and how they trigger synaptic transmission, which allows brain cells to talk to each other. We’ve learned how stimuli in the external world activate sensory neurons, enabling us to see, hear, and smell, for example, and we’ve identified the motor neurons controlling our muscles, which empower us to produce specific body movements to react to those stimuli.

What we don’t understand is how all of these processes work together to generate higher order perception and thought, let alone emotion. Sure, we may understand how photons of light activate specific neurons in your retina, but how are these visual signals translated by your brain to make you appreciate a sunset or recognize your mom’s face? Even if we understood everything about how the brain interprets sensory signals, how does it integrate different kinds of information to make a decision, so that you’re not just responding to what you see or hear but also acting based on your prior experience, physical and emotional state, and so on?

example of a neural circuit, drawn by Santiago Ramon y Cajal (Wikimedia Commons)

The brain accomplishes these impressive feats by using neural pathways, or “circuits”, to process information in complex ways. Each neuron receives input signals from other neurons or from an external stimulus, then processes or integrates that information in some way, and finally transmits the modified signal to other neurons which do the same. The pathway might start with neurons in the retina responding to single photons of light, but it ends with some neuron somewhere saying “Aha, this is my mom’s face!” Or, “Aha, this is a doughnut and I am starving, so I better reach out to grab it before someone else does!” (In my lab, speed is essential for claiming custody of an unattended doughnut.)

So all we need to do is identify which neurons comprise a neural circuit for doing something, and then examine how information is integrated and transformed along each step of this pathway. Simple, right? But wait, remember how there are ~100 billion neurons and ~100 trillion connections in the human brain? Yeah, not so simple anymore. That’s why each of us studying the brain has to focus on a very specific question as well as a specific part of the relevant neural pathway, slowly unveiling how the brain accomplishes a particular task.

With the explosion of neuroscience research over the last couple decades, we’re starting to truly understand how neurons function together in circuits—how they process sensory information, make simple decisions, change with experience, and much more. But there are still some really tough questions that we’ve barely begun to address. Like, what’s going on in your brain when you have a “random thought” that seems to arise from thin air? Why do we form emotional connections to certain people, places, or objects, but not others? How do our unique brains explain our individual differences—our distinctive personalities, passions, and talents?

The answers to these questions may seem elusive, but I believe they’ll one day reveal themselves. We just have to hope that our brains have made us smart enough to eventually comprehend their inner workings.

People often repeat the saying, “If our brains were simple enough for us to understand them, we’d be so simple that we couldn’t.” Maybe that’s true, but I doubt it. With the collective knowledge gained by brilliant neuroscientists of the past, present, and future, combined with new technologies allowing us to probe neural function in ways hardly imaginable in the last century, I’m betting that someday humans will unravel the fundamental mysteries of the brain.