How your brain forms memories unveiled

A team of researchers has made a spectacular discovery, for the first time in human studies, of how memories are formed and new learning takes place.

A collaboration between Matias Ison and Rodrigo Quian Quiroga at the University of Leicester and Itzhak Fried at Ronald Reagan UCLA Medical Center revealed how a neuron in the brain instantly fired differently when a new memory was formed.

The scientists showed patients images of a person in a context e.g. Jennifer Aniston at the Eiffel Tower, Clint Eastwood in front of the Leaning Tower of Pisa, Halle Berry at the Sidney Opera House or Tiger Woods at the White House. They found that the neuron that formerly fired for a single image e.g. Jennifer Aniston or Halle Berry, now also fired for the associated image too i.e. the Eiffel Tower or Sidney Opera House.

The remarkable result was that the neurons changed their firing properties at the exact moment the subjects formed the new memories, the neuron initially firing to Jennifer Aniston started firing to the Eiffel Tower at the time the subject started remembering this association, said Quiroga.

Moreover, they observed these changes after just a single presentation. This is a radical departure from previous experiments in animals where changes have been observed mainly after long training sessions. This is critical to understanding the neural processes underlying real-life memory formation, as in real life we are not repeatedly exposed to an event in order to remember it, just one exposure is enough.

Lead author Ison said that this is the first study to look at how a single neuron correlates learning of new contextual associations in the human brain. The single neuron underpinning of memory formation has previously been addressed only by animal studies, which can only offer a limited account of how single events can lead to new episodic memories.

The study appears in journal Neuron.