When you concentrate, there is a resultant decrease in the disorder of the neural system. As concentration increases, the tendency of the mind to waver and scatter decreases. The mind is more sharply focused. So when we concentrate, we are increasing the synchronicity of a specific group of neurons and silencing unrelated neuronal activity. In scientific parlance, concentration decreases the entropy of the neuronal apparatus. Just as the entropy of matter drops to near-zero levels when we approach Absolute Kelvin, similarly, the neuronal disorder keeps waning as we concentrate. The neuronal firing decreases in amplitude as well as frequency. So would the propagation across various networks.
In the waking state, when you consciously attempt to decrease the entropy of the nervous system, it is referred to as meditation. As the entropy of the neurons keeps decreasing, a state of calmness is perceived. As this progresses further, the neurons start becoming synchronous. That is, they neither modulate nor amplify any incoming signal. They just resonate in harmony. As this orchestra gets more in sync, you experience varying states of bliss and happiness. Till what is presumably the final state of zeroentropy, where all 100 billion neurons function in total unified quantum coherence. The Bose-Einstein condensate equivalent of the neuronal system is what may be termed as Samadhi.