A very dense network of processes occupies the space between the cell bodies of the neurons, neuroglia (cells that support and protect neurons), and blood vessels. This space (the neuropil) represents 90-98% of the volume of the human cerebral cortex, with an estimated one billion synapses per cubic millimeter of neuropil.
分析大脑的主要问题在于其突触连接的极端复杂性。一个非常密集的过程网络占据着神经元细胞体、神经胶质（支持和保护神经元的细胞）和血管之间的空间。这类空间（神经毡，neuropil）占据了人类大脑皮层总体积的90—98%，每立方毫米神经毡大约包含十亿个突触。