Summary: Inhibition in Neuroscience
The term inhibition has been used in neuroscience since
the 19th century (Smith 1992). It has many different
meanings, ranging from mechanisms governing behav-
ioral output, to circuits between brain regions, to cellular
firing, to enzymes. Early physiological experiments dis-
covered inhibition in the simple reflex (Fig. 1A).
Subsequent physiological experiments demonstrated the
descending influence of the central nervous system on
motor output, the heart, and other organs (Smith 1992).
Other meanings of the concept apply at a finer level of
analysis. Within the brain, some neurons are inhibitory
(e.g., those using Gamma-aminobutyric acid, GABA).
When a GABA-containing neuron is active, it releases
GABA across the synaptic cleft, and this can induce inhi-
bition on the target neuron in the form of an inhibitory
postsynaptic potential. Inhibition at this cellular level plays
out at both a circuit and a systems level. Figure 1B shows
input from layer 6 of the frontal cortex to a cell in the retic-
ular nucleus, which then sends a GABAergic projection