Unconscious - and Remarkably Complex! - Inference

Although described as a master computer, the brain is fundamentally more complex and its processes far more subtle than those of any current computer design. With the advantage of parallel operation of neuronal populations, the brain manages and controls a wide variety of tasks simultaneously, reliably, and with rapid precision. Indeed, much of the brain's work proceeds even in the absence of an individual's conscious awareness.

All brain activity results from electrical and chemical communication among neurons (the primary signaling cells of the brain), each of which can communicate with other neurons using signals at rates of up to 1,000 events (impulses) per second. To understand the brain, neuroscientists must measure and analyze the rapid changes in neuronal signaling activity that occur over the vast networks of cells and connections. The scope of this endeavor is immense. It is estimated that the human brain contains more than 100 billion neurons, and each neuron maintains an average of about 1,000 connections, called synapses, with other neurons. Some neurons have as many as 200,000 synapses. During each moment of daily life, neural signals may be transmitted across any of approximately 100 trillion synapses.

Constance M. Pechura and Joseph B. Martin, eds., Mapping the Brain and Its Functions (National Academies Press, 1991)