Our brains are plastic; they change over time based on the stimulus they’re given. The way events in our life change the nature and structure of our brains—i.e., learning—is the focus of this chapter. As Sapolsky shows, this process is all about the varied ways neurons connect to each other.

“The essence of learning” (139) is the synaptic connection between neurons. In creating synaptic connections, one neuron sends repeated signals containing the neurotransmitter glutamate through the synapse (the gap between the two neurons) to another neuron, which finally activates once its activation threshold is reached. Now neuron A can send information through to the receptive neuron B. This first activational burst of neuron B causes long-term potentiation (LTP), a prolonged increase in the responsiveness of the synapse to subsequent glutamate signals. In a highly complex sequence of events, Sapolsky outlines the basis of learning and memory: strengthened connections between particular neurons.

LTP occurs throughout the nervous system, facilitating our ability not just to remember explicit facts but also conditioned responses like fear, craving, and sensations. Creating and strengthening memory can also occur through the creation of new dendrites—the ends of the neuron receptive to others.