Neurotech: From Signals to Behavior

Part 2 of a 12 part Neurotech series in partnership with Scientific American

You’re sitting outside posting pics of a beautiful day to Facebook when it hits you. A spicy, cheesy, carne asada-ey deliciousness that can only mean one thing: a burrito truck is near. Hound-like you hunt your lunch. An impending Mexicali meal will soon satiate your suddenly growling stomach. You finally arrive, brave a bending line, order, and exchange a five dollar bill for possibly the best burrito of your life. But what if when you reached the front of the line, you had only a credit card and the cash-only foodtruck had turned you away? One step awry in this situation and you would have had to live your afternoon burritoless, grumpy and hungry.

Neuroscientists often ponder similar questions. Not about burritos, but rather how alterations in sequences of action potentials can lead to variations in outcomes. How does cellular activity allow a brain to make decisions or formulate what to do next? How does what you think relate to what you do?

A neuron spikes, sending an action potential along its axon to be received by dendrites of other cells found downstream in its signal pathway. Charting these pathways allows us to decipher causational information flow in the brain, which can be useful if we want to understand the neurological basis of things like memory formation or intelligence.

As if it is not complicated enough, a brain is no uniform single organ. Within it are many substructures. The hippocampus, for example, plays a primary role in memory formation and the thalamus helps the brain process a multitude of sensory information. Each structure has its own role in a brain’s overall function. They are differentiated in part by unique arrangements and functional activity of cell types that project to and receive spikes from other parts of the brain. We recognize that these pathways are core to neurological function; however, little is known of their detailed compositions.

“A typical neuron in the mammalian brain receives thousands of synaptic inputs and sends out information through thousands of output synapses. Experience alters the brain by making, modifying or eliminating these synapses. To facilitate the study of these processes in living brain tissue, the individual parts of the neuron can be labeled using fluorescent proteins. In this image, one neuron is labeled in red using a cytosolic dye introduced through a microelectrode. Green puncta are individual synapses (each synapse is around 1 micron in size).” Image by Venkatesh Murphy, Harvard University

Neurons are tiny — hundreds of them would fit across the tip of a single human hair. This makes them challenging to see and measure. That’s where neurotech comes in. Microelectrode recording devices allow researchers to monitor activity of hundreds of neurons at single cell resolution in different parts of the brain during behavior.

Behavior includes things we may not think about, like sleep. During the night, a brain replays the day’s memories, consolidating a few of them into the mind’s long term archives. During subsequent days, weeks, and even years, the brain can alter those memories. Research indicates that memory modifications occur at cellular precision deep within the brain, which means that scaled single neuron resolution monitoring stands to illuminate the mechanisms of retaining and maintaining knowledge.

Brains do much more than think. Walking or holding a phone is something most of us do every day and take for granted. But one severed step in a neural pathway can be enough to prohibit its function. Take the case of Ian Burkhart. In 2010 he broke his neck. At 23 years old, he is quadriplegic. For now. Researchers at Ohio State University successfully implanted a neuroprosthetic microelectrode into Ian’s brain, letting him move his arm by thinking. How long will it be before neurotech allows paraplegics to walk again?

Tune in to next week’s MIT Neurotech as we explore how microfluidics shines light on the molecular basis of cancer.

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