cognitive levels of human brain activity. It is difficult if not impossible for the average person to cause the heart to palpitate through conscious thought.

It is easy to relate the neural chassis to computer architectures. Through its connection to the various reactive motor facilities located throughout the body, this facility functions very much as an independent, self-contained input/output channel. That is, certain stimuli, when detected by peripheral sensors connected to the human distributed nervous system, elicit immediate reactions, such as that of the muscle system causing a foot to jerk or the whole body to jump. The pathway of the signal from the receptor to a point of control and then back to the appropriate muscle can be of different length. A computer component analogous to the autonomic components of the body is a fan that moderates the temperature of internal circuitry, or a surge protector that automatically filters spurious electrical events. A component analogous to external sensori-motor elements is the apparatus that eliminates offensive network packets of information at the source in case of computer attacks that attempt to flood an input channel of a secure core to deny its processing of otherwise valid information.

The Reptilian Brain

In the evolution tree, reptiles precede mammals. A contrasting study between reptiles and mammals allows studying differential properties of the organism attached to particular characteristics of the brain. The upper neural apparatus of reptiles accounts for behaviors like territoriality, courtship, and submissive displays, as well as hunting, grooming and mating activities. By comparing those behaviors across reptiles, as well as across other non-mammalian vertebrates, it is possible to recognize patterns of behaviors associated with aspects of the brain of reptiles. Through anatomical, chemical, neurological and surgical work, as well as phylogenetic and ontogenetic considerations, it is possible to define a prototypical model for the upper brain of reptiles. From there, it is possible to practice further experiments exploring the functional properties of the brain, in reptiles as well as in other species. MacLean calls this proto-reptilian brain formation the striatal complex, but many, including him, refer to it also as the reptilian brain, and we will follow that practice.

The next step, obviously, is to refine the model of the reptilian brain by comparing its formation with similar constructs in mammals, and eventually in humans. It is from identifying in reptiles and mammals similar constructs that MacLean comes to consider the reptilian brain as one of the three components of the triune brain. A natural hypothesis is that behaviors associated with the reptilian brain would be forming a pattern extending from reptiles to the full range of mammals. While this can be readily verified in some mammals through intrusive operations, it is more difficult in upper mammals and humans. A combination of medical observations, physiological and psychological experiments, and new non-invasive techniques like functional magnetic resonance imaging allow investigating the hypothesis in greater length. The reptilian denomination obviously does not mean that we are all running around with the brain of a lizard in our heads, despite our predilections towards associating people with reptiles in a very pejorative manner. Rather it is simply an observation that the human brain is an artifact of an evolutionary process, and evolutionary processes tend to build upon successful traits rather than discarding such traits and starting over again. This said, we are ready to consider mammals, an important step because it allows us to enter the realm of emotions, that we have already identified as a central element in the evaluation of trust infrastructures of computer networks.

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