How new memories are formed in brain decoded

Neurons in a specific brain region play a key role in rapidly forming memories about every day events, a new study has found, paving the way for new methods to fight Alzheimer's and other neurological diseases.
The study examined neurons in the medial temporal lobe associated with episodic memory, the brain's ability to consciously recall experienced events and situations like running into an old school friend at the opera.
Episodic memory logs these unique experiences and relies on the very rapid formation of new associations in the brain.
The team was able to record individual neurons in the medial temporal lobe and found that the cells changed their firing to encode new associations at the exact moment of the experience, said study senior author Dr Itzhak Fried, from the University of California - Los Angeles Health Sciences.

"This study goes into the heart of the neural code underlying one of the most fundamental aspects of human cognition and memory, namely the formation of associations.
"The astonishing finding was that this basic code is so explicit at the level of individual neurons in the human brain," Fried said.

The study involved 14 patients with severe epilepsy who were implanted with electrodes in their brains to identify the seizure focus for possible surgical intervention.
The brain recordings in the study, where more than 600 medial temporal lobe neurons were identified, took five years and involved showing the patients pairs of unrelated pictures, one of a person and another of a place, to construct a meaningful association modelling the episodic memory of meeting a person in a particular place, said study first author Matias J Ison, from the University of Leicester in the UK.

The patients were shown about 100 pictures of celebrities, animals and places, and the research team analysed the encoding activity of the individual neurons in the brain as the images registered.
With this first analysis, the team was able to find neurons that responded to one or more pictures.
During a second analysis, the team created contextual composite images showing a person at a place - for example, meeting Clint Eastwood at the Tower of Pisa - and followed the activity of individual neurons while the patients learned these associations.
"This study looks at the single neuron correlates of the learning of new contextual associations in the human brain, and we were able to show for the first time that the speed at which complex associations are encoded is compatible with the basic mechanisms of episodic memory creation," Ison said.

"The astonishing fact was that these changes were dramatic, in the sense of neurons being very silent or very active, and that it occurred at the exact moment of learning," said Ison.
Fried said understanding the underpinnings of episodic memory formation is a central problem in neuroscience and may be of important clinical significance because this type of memory is affected in patients suffering from Alzheimer's and other neurological diseases.
The study appears in the journal Neuron.