First ever study records memory being encoded in individual neurons.

In the first study of its kind researchers from UCLA and the University of Leicester found that neurons in a specific brain region play a key role in rapidly forming memories about every day events, a finding that may result in a better understanding of memory loss and new methods to fight it in Alzheimer’s and other neurological diseases.  Specifically, the new 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. The team explain that episodic memory logs these unique experiences and relies on the very rapid formation of new associations in the brain.  The opensource study is published in the journal Neuron.

The current study recorded 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.  The team state that the findings 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 results show that this basic code explicitly at the level of individual neurons in the human brain.  Recording such activity of even one lonely cell in a multitude of billions of neurons in the brain of a patient on a hospital ward is a technical achievement that only a few places in the world can achieve.

The current study involved 14 patients with severe epilepsy who were hospitalized at UCLA and implanted with electrodes in their brains to identify the seizure focus for possible surgical intervention. The brain recordings in this 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 modeling the episodic memory of meeting a person in a particular place.

The patients were shown about 100 pictures of celebrities, animals and places, and the researchers analyzed 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.

The results show how a single neuron correlates the learning of new contextual associations in the human brain, and it was shown for the first time that the speed at which complex associations are encoded is compatible with the basic mechanisms of episodic memory creation.  The group add that they had hypothesized that they’d be able to see some changes in the firing of the neurons. However, it was shown 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.

The team state that 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.  They go on to add that the loss of memory function is one of the most devastating afflictions of the human condition.

The team are now engaged in a multidisciplinary effort to develop both software and hardware for a neuro-prosthetic device that may restore episodic memory function in neurological patients.

Source:  University of Leicester


Synaptic potential.  Close-up view of a motor neuron, revealing its synaptic connections from axon terminals (potentially thousands) of other neurons.   © 2015 Hybrid Medical Animation.
Synaptic potential. Close-up view of a motor neuron, revealing its synaptic connections from axon terminals (potentially thousands) of other neurons.
© 2015 Hybrid Medical Animation.