How do the many millions of neurons -the tiny building blocks of the brain- work together to allow us to do things like remember what went on earlier in the day, and to recall it later in the evening, or even years afterwards? Each neuron receives signals from thousands of other neurons, then based on this input decides when to generate its own signals and transmit them to another set of thousands of neurons. To try to understand this electrical code of the neurons, we want to measure the signals received and sent by individual neurons.
There are many ways to measure such electrical activity, but only a few ways can be done in the brains of animals that are free to run around.Â Before we started our work, one of the most sensitive measuring methods (called whole-cell recording) was only possible in pieces of brain cut out and placed under a microscope, or in animals that had to remain absolutely still. We wanted to develop a way to do these same sensitive measurements in rats while they ran around and learned various mazes. This is because we want to study how the brain learns in real world situations, and specifically because how rats learn mazes could teach us about how humans form memories of facts and events from daily life. The two major tasks we had to accomplish were to make the measuring equipment small enough so a rat could carry it around, and to figure out a way to keep everything stable enough so that we could keep measuring even while the rat turned, ran, and bumped into walls.Â We succeeded with both, and though the procedure still needs additional improvement, we believe it holds great promise for revealing how individual neurons give rise to higher mental processes.