[Decision making: biological bases and limitations]

In the human brain, simple molecules and complex circuits are constantly making decisions which are indispensable for our survival and also to accomplish a variety of daily activities such as walking, memorizing, conversing, composing music, painting or poetry.... All are the result of the integration of many neural systems that perceive many and simultaneous visual, tactile, auditory and/or mental stimuli. Once synthetized, they are immediately transmitted to the corresponding executive systems, thus completing the fascinating functional loop of decision-making: a) perception of stimuli or information which originate in the environment, b) selection and elaboration of the decision which is considered more appropriate or attractive according to personal experience or intuition and c) execution. If these neural nets have been damaged or haven failed to develop the mechanisms of facilitation or inhibition that govern them become unbalanced. If inhibition is reduced, excessive and violent behaviour is expressed as in patients suffering from manic phases. Conversely, if inhibition is excessive, decision making mechanisms are not operative. In either case, behaviour is not "reasonable" and does not follow prototypical patterns. All these processes must be the consequence of a constant molecular activity full of micro-decisions whose effectiveness depends on the histological and biochemical integrity of the neurons. This microenvironment is responsible for all types of decisions of all forms of life and represents one of the fundamental successes of evolution.