Where does inhibition collide?

The reduction of a neuron's probability of firing when an inhibitory input drives its membrane away from threshold, typically through GABAergic synapses that open chloride or potassium channels and produce inhibitory postsynaptic potentials. Isaacson and Scanziani's 2011 How inhibition shapes cortical activity reviewed how such inhibition, held in balance with excitation, sharpens tuning, controls timing, and gates the flow of signals through cortical circuits. The referent is a physiological event at a synapse and membrane, measured in millivolts and conductance, not a suppressed action, a slowed enzyme, or a reticent temperament.[1]

Unit

A hyperpolarising or shunting input that lowers a neuron's firing probability

Recovery means

The membrane returns toward its resting potential as inhibitory conductances close and the chloride gradient is restored

Measured by

Recorded by patch clamp and intracellular electrodes as inhibitory postsynaptic potentials or currents, and inferred from excitation and inhibition balance

The executive ability to suppress a prepotent or already initiated response when it is no longer appropriate, one of the core functions of cognitive control probed by stop-signal, go/no-go, and Stroop tasks. Logan and Cowan's 1984 On the ability to inhibit thought and action modelled the stop-signal task as a race between a go process and a stop process, letting the latency of the unseen act of inhibition be estimated. The referent is a controlled mental act that cancels a behaviour, timed in milliseconds of stopping latency, not an inhibited synapse, a blocked enzyme, or a shy disposition.[2]

Unit

The suppression of a prepotent response, indexed by stop-signal reaction time

Recovery means

Not applicable

Measured by

Estimated from stop-signal reaction time in the stop-signal task, and from error and interference scores in go/no-go and Stroop paradigms

The reduction of an enzyme's catalytic rate by a molecule that binds it, whether competitively at the active site, noncompetitively at another site, or by other mechanisms, and quantified by the inhibition constant Ki or the half-maximal concentration IC50. Cheng and Prusoff's 1973 paper derived the relationship between the concentration of inhibitor that halves an enzymatic reaction, its I50, and the true binding constant Ki, correcting for substrate concentration. The referent is a molecular binding event that slows catalysis, measured in reaction rates and dissociation constants, not a quieted neuron, a cancelled action, or a withdrawn person.[3]

Unit

A fractional loss of catalytic rate from inhibitor binding, indexed by Ki or IC50

Recovery means

Reversible inhibitors dissociate as their concentration falls and activity is restored, while irreversible inhibitors require new enzyme synthesis

Measured by

Determined from enzyme kinetic assays as changes in velocity across substrate and inhibitor concentrations, yielding IC50 and, via the Cheng and Prusoff relation, Ki

A temperamental disposition, evident early in childhood, to react to unfamiliar people, objects, and situations with restraint, withdrawal, and physiological arousal rather than approach. Kagan, Reznick, and Snidman's 1988 Biological bases of childhood shyness identified consistently inhibited and uninhibited children and linked the inhibited profile to heightened sympathetic and neuroendocrine reactivity. The referent is a stable behavioural style of a whole person facing novelty, assessed by observed reticence and arousal, not a synaptic event, a stopped response in a task, or an inhibited enzyme.[4]

Unit

A disposition to withdraw from novelty, rated from observed restraint and arousal

Recovery means

Not applicable

Measured by

Assessed in behavioural observation of children meeting unfamiliar people and settings, alongside heart rate, cortisol, and other markers of arousal