Heterostasis (cybernetics)

Heterostasis is a term belonging to the domains of the biological, medical, system, and computer sciences. It is linguistically derived from two classic Greek morphemes meaning 'different states'. It is a neologism intended to connote an alternative but related meaning to its lexical sibling Homeostasis, which means 'same state'. Any device, organ, system or organism capable of Heterostasis (multistable behavior) can be represented by an abstract state machine composed of a characteristic set of related, interconnected states, linked dynamically by change processes allowing transition between states. An example is the common automobile accessory called a cruise control, which maintains a vehicle's speed without the driver's input, e.g. by the gas pedal. (See also Servomechanism.) The difference between a Homeostat and a Heterostat is sometimes decided as much by the end user as the system designer. The space-heater Thermostat on the wall of a house is intended to be left at one setting which is deemed comfortable. However, that same thermostat dial must also (occasionally) be adjusted dynamically, because it is the only way to change the room's temperature.

The term Homeostasis was coined by Walter Cannon. Although the term 'Heterostasis' is an obvious rearrangement (by syntactically substituting the prefix 'Hetero-' for its dichotome 'Homeo-', and likewise swapping the semantic reference, from 'same'/'single' to 'different'/'many'), the endocrinologist Hans Selye^[1] is generally credited with its invention. An excellent overview of the two concepts is contained in the Cambridge Handbook of Psychophysiology, Chapter 17.^[2] Selye's ideas were used by Gunther et al.,^[3] in which dimensionless numbers (allometric invariance analysis) were used to investigate the existence of heterostasis in canine cardiovascular systems.

Alternative terminology

The equivalent term Allostasis is used in biological contexts, where state change is analog (continuous), but Heterostasis is sometimes preferred for systems which possess a finite number of distinct (discrete) internal states, such as those containing computational processes. The term Servomechanism is usually used in industrial/mechanical situations (non-biological and non-computational) where it often applies to analog state change, e.g. in a Direct Current Servomotor.

References