Scientists redefine how the brain learns information

Neurons, shown above, are cells in the brain that transmit chemical signals. (credit: Courtesy of Wikimedia Commons) Neurons, shown above, are cells in the brain that transmit chemical signals. (credit: Courtesy of Wikimedia Commons)

At Carnegie Mellon, students often find themselves spending long nights cramming for tests. Hours of staring at a book can lead to headaches and sometimes frustration as to why something just doesn’t make sense. Clouded by this frustration, many students can sometimes forget the incredible ability of the human brain; it constantly rewires the massive network of nerves to ensure that by the test, the student has mastered the concept at hand.

Scientists have been intrigued by how the brain works for years, and with every day they understand more about what makes thinking, learning, and memory possible. Sandra J. Kuhlman, assistant professor of biological sciences at Carnegie Mellon, explored how inhibitory neurons in the brain function during critical periods of learning. Kuhlman collaborated with researchers at the University of California, Los Angeles and University of California, Irvine; their results were published in the journal Nature.

The neural network can be pictured as a massive system of roads, with thousands of delivery trucks carrying messages from one part of the brain to another. These networks are made up of neurons, nerve cells that transmit electric signals across the cell and release chemicals that generate electrical stimulation of neighboring cells. The propagation of these electric signals around the brain is vital to the brain’s function.

Roads are often connected at intersections governed by traffic lights that control the movement of cars. In the brain, the neural network is constantly being modified by excitatory neurons that act as green lights, allowing for the generation of electrical signals and thus the flow of information from one cell to another. Conversely, inhibitory neurons act as red lights, preventing the propagation of electrical signals.

Kuhlman and her team wanted to observe the workings of inhibitory neurons during times of heightened learning by exposing mice to new events and stimulating a model for learning. However, 80 percent of neuron cells are excitatory, which posed a challenge to the project. “If you’re just going blindly and observe cells, you are going to learn about excitatory cells because that’s what you will bump into,” Kuhlman said. Such ubiquity makes it difficult to learn about the specific neurons they were interested in.

However, the development of new technologies enabled the study to label different parts of the mouse brain using dyes. Kuhlman’s team utilized this, along with powerful microscopes, to identify the inhibitory neurons and used electrodes to measure active electrical stimulations.

Prior to their experiment, the typical line of thinking was that inhibitory neurons release the chemical neurotransmitter gamma-Aminobutyric acid (GABA); it had been hypothesized that increased GABA enabled the brain to learn things quickly. The researchers, however, chose to investigate this theory.

After teaming with collaborators at UC Irvine, Kuhlman explained that the new ideas brought forth by the new members of the team questioned the theory about GABA, which propelled the team forward. After the experiments, the team learned that when a person has a new experience, inhibition is reduced and less GABA is produced. This leads to the remodeling of circuits in the brain.

Kuhlman found it interesting that “this was only seen in young brains. Older brains can also learn but the inhibition is removed differently and is harder to invoke.” The next step of her research may be to understand how the mechanism works in older brains.

The project challenged a paradigm and changed the way scientists understand the role of inhibitory neurons in these critical periods of learning.