You probably have a general understanding of the human brain: a network of nerve cells connected by synapses. Complex or abstract ideas emerge as a result of the firing of many of these nerve cells, or neurons. This means that a concept or memory or idea is the result of a distributed pattern of neural activity. In contrast to computer memory, which always follows the same pattern of 1s and 0s, it's more like networks in our brain weave a new tapestry every time we think about something. This understanding is common to most of us lay people who know a little about neurology and the brain, or who are interested in AI and the attempts to replicate human intelligence.
Unfortunately, you may be badly out of date. As it turns out, in human brains, we also have a specialized type of cell called a concept neuron, which does what was long thought to be impossible: each of these cells encodes entire concepts, so that that single neuron fires whenever you’re exposed to a stimulus relating to that concept, or even when you think about it without an external stimulus. This would be like having a single neuron that fires when you see a photograph of your grandmother, hear her voice, read her name or perhaps even smell her familiar perfume. This single neuron thus has semantic invariance for the concept of your grandmother. This means that it fires whenever your grandmother is the topic of thought, regardless of the context or medium or the sense that stimulates your thought of her.
