**2.2 Mental processes as emergent phenomena**

Much of modern scientific medicine is reductionist, involving a search for ultimate basic causes of disease. This paradigm for scientific research follows naturally from the extraordinary success of physics in the last century, with its search for the fundamental laws of the universe. But that model is giving way to a new vision of the universe as a complex dynamical system, one in which fundamental laws may in fact be emergent properties of the system (Laughlin, 2005).

Emergent properties are those that result from the organization of individual parts and do not exist apart from the organizational whole. The saying that the whole is more than the sum of the parts is a description of an emergent property. The process of cell division, for example, is an emergent process that cannot be explained or studied using quantum mechanics – even though quantum mechanics is a good description of how atoms interact, and a cell is made up of many atoms, each obeying the fundamental physics of quantum theory. Similarly, the difference between a well-written high school essay for a college admissions committee and a Pulitzer Prize winning novel is not to be found in grammar and spelling, even though proper spelling and grammar are essential to the meaning of literature. Literature, genre and metaphor are emergent phenomena, more than words and sentences.

Developing neurotechnology, including devices and analysis methods, may be the most challenging subfield of biomedical engineering because the phenomenon of interest, a mental state or a complex set of behaviors that may indicate a diagnosis of a mental disorder, is an emergent phenomenon. Human behavior is controlled by the brain, which is ultimately a complex network of neurons that transmit electrochemical signals. Thought and behavior cannot be understood or measured by studying neurons (or genes) alone. Psychiatric biomarkers that focus on complex system properties may be the most informative measurements for assessing mental state. We now present a survey of complex system properties that can be computed from time series of brain electrical activity. Neural activity is electrochemical activity. Taking into account degradation due to the skull and scalp and the introduction of noise by the electronic sensors, EEG may be the most direct measurement of brain function that is possible. Thought might be considered an emergent phenomenon of neural electrical activity.
