Imagine that while you are enjoying your morning bowl of Cheerios, a spider drops from the ceiling and plops into the milk. Years later, you still can't get near a bowl of cereal without feeling overcome with disgust. Researchers have now directly observed what happens inside a brain learning that kind of emotionally charged response. In a new study published in January in the Proceedings of the National Academy of Sciences, a team at the University of Southern California was able to visualize memories forming in the brains of laboratory fish, imaging them under the microscope as they bloomed in beautiful fluorescent greens. From earlier work, they had expected the brain to encode the memory by slightly tweaking its neural architecture. Instead, the researchers were surprised to find a major overhaul in the connections.

The brains of almost all animals contain a network of crisscrossing nerve cells, also known as neurons. Each nerve cell consist of three main parts -- the soma (cell body), an elongated axon, and several branching dendrites. For the longest time, scientists believe that the somas were the only regions in neurons that generated electrical spikes in order to connect and communicate with other neurons, and that the dendrites were just passive conduits of these pulses. However, according to a study published in the latest edition of the journal Science, this model of how neurons function may not be entirely accurate. The study on lab rats, carried out by a team of researchers from the University of California, Los Angeles (UCLA), reveals that dendrites are electrically active in animals that are moving around freely and that these structures generate nearly 10 times more spikes than somas.