A single neuron can encode an association between two concepts.
In these days of modern scanning equipment, individual neurons can be seen firing in the brains of those being monitored. This has had a remarkable effect on the study of the brain.
Matias Ison, Rodrigo Quian Quiroga and Itzhak Fried, in 2015, studied 600 individual neurons in epileptic patients. They called a neuron in one patient the “Jennifer Aniston neuron” because it would fire every time that person saw a picture of the actress Jennifer Aniston.
Following up on the discovery of this Jennifer Aniston neuron the experimenters would show participants pictures of famous people or family members to discover which neurons would fire in response to those individuals. They then showed a picture of that person at a famous landmark. For example, once they had established a neuron firing in response to any picture of Clint Eastwood, they would show a picture of Clint Eastwood at the Leaning Tower of Pisa. That neuron would then fire even if the person was shown a picture of just the Leaning Tower of Pisa.
This experiment showed that the single neuron had encoded an association between two concepts (Clint Eastwood and The Leaning Tower of Pisa) instantaneously, after just one exposure to the picture.
Ison, Matias J. et al. (2015). Rapid Encoding of New Memories by Individual Neurons in the Human Brain. Neuron , Volume 87 , Issue 1 , 220 – 230