Where does activation collide?

The minimum energy that colliding molecules must possess for a chemical reaction to proceed: it is the height of the barrier between reactants and products, and it governs how sharply a reaction speeds up as temperature rises. Arrhenius's 1889 study of cane sugar inversion introduced the exponential relation now named for him, in which the reaction rate depends on this barrier energy and the absolute temperature. The referent here is a threshold on an energy landscape, measured in kilojoules per mole, not a state of bodily arousal, a course of therapy, or the output of a computing unit.[1]

Unit

A threshold energy per mole of reactant, in kilojoules per mole

Recovery means

Not applicable

Measured by

Estimated from the slope of a plot of the logarithm of reaction rate against inverse temperature, known as an Arrhenius plot

A general dimension of how energised or aroused an organism is at a given moment, running from deep sleep to intense excitement and expressed across the body in signals such as heart rate, muscle tension, and skin conductance. Duffy's 1957 paper argued that this level of activation, rather than a list of named emotions, is the useful underlying variable for describing behaviour, a view that fed later arousal theory. The referent is a graded physiological and psychological state of a whole organism, read from bodily signals, not a barrier in a chemical reaction, a treatment for low mood, or a number inside a network.[2]

Unit

An organism's momentary level of arousal, placed on a low-to-high continuum

Recovery means

Activation falls back toward a resting baseline once a rousing situation passes

Measured by

Indexed by physiological signals such as heart rate, skin conductance, muscle tension, and electroencephalographic pattern

A structured psychotherapy for depression that works by helping a person schedule and re-engage in rewarding, values-based activity, on the premise that withdrawal and avoidance keep low mood in place. In a 1996 component analysis, Jacobson and colleagues found that this activation part of cognitive-behavioural therapy performed as well as the full package, which helped establish behavioural activation as a treatment in its own right. The referent is a clinical procedure delivered to a patient over weeks, judged by symptom change, not an energy barrier, a bodily arousal level, or a unit in a computational model.[3]

Unit

A course of therapy for one patient, delivered over a series of sessions

Recovery means

Not applicable

Measured by

Evaluated by change on depression rating scales and by counts of scheduled activities the patient completes

In an artificial neural network, the activation of a unit is the value it outputs after summing its weighted inputs and passing them through a nonlinear function, which decides how strongly it passes signal onward. McCulloch and Pitts's 1943 model of an all-or-none threshold neuron gave the first formal account of such a unit turning on or off, the ancestor of today's activation functions. The referent is a number computed inside a mathematical model, set by weights and inputs, not a chemical threshold, a state of bodily arousal, or a clinical treatment.[4]

Unit

A single unit's output value, produced by its activation function

Recovery means

Not applicable

Measured by

Read directly as the numeric output of a unit for a given input, after its activation function is applied