Handbook of Psychology

298 Pain Management

INTEGRATIVE, MULTIDIMENSIONAL MODEL—
GATE CONTROL THEORY

The “rst attempt to develop an integrative model designed to
address the problems created by unidimensional models and
to integrate physiological and psychological factors was the
gate control theory (GCT) proposed by Melzack and Wall
(1965). Perhaps the most important contribution of the GCT
is the way it changed thinking about pain perception. In this
model, three systems are postulated to be related to the pro-
cessing of nociceptive stimulation„sensory-discriminative,
motivational-affective, and cognitive-evaluative„all of
which contribute to the subjective experience of pain.
Melzack and Wall emphasized the central nervous system
mechanisms and provided a physiological basis for the role of
psychological factors in chronic pain.
The GCT proposes that a process in the dorsal horn
substantia gelatinosa of the spinal cord acts as a gating mech-
anism that inhibits or facilitates transmission of nerve
impulses on the basis of the diameters of the active peripheral
“bers as well as the dynamic action of brain processes.
Melzack and Wall (1965) postulated that the spinal gating
mechanism was in”uenced by the relative amount of excita-
tory activity in afferent, large-diameter (myelinated) and
small-diameter (unmyelinated nociceptors) “bers conver ging
in the dorsal horns. They also proposed that activity in A-beta
(large-diameter) “bers tends to inhibit transmission of noci-
ceptive signals (•closes the gateŽ) while activity in A-delta
and c (small-diameter) “bers tends to facilitate transmission
(•open the gateŽ). The hypothetical gate in the dorsal horn
modulates the sensory input by the balance of activity of
small diameter (A-delta and c) and large-diameter (A-beta)
“bers (see Figure 13.2).
As an important innovation, Melzack and Wall (1965)
postulated further that the spinal gating mechanism is in”u-
enced not only by peripheral afferent activity but also by

efferent neural impulses that descend from the brain.They

suggested that a specialized system of large-diameter, rapidly

conducting “bers (the central control trigger) activate selec-

tive cognitive processes that then in”uence, by way of de-

scending “bers, the modulating properties of the spinal

gating mechanism. Melzack and Wall speculated that the

brain stem reticular formation functions as a central biasing

mechanism, inhibiting the transmission of pain signals at

multiple synaptic levels of the somatosensory system.

The GCT maintains that loss of sensory input to this com-

plex neural system, such as occurs in neuropathies, causalgia,

and phantom limb pain, tends to weaken inhibition and lead

to persistent pain. Herniated disc material, tumors, and other

factors that exert pressure on these neural structures may op-

erate through such losses of sensory input. Emotional stress

and medication may also alter the biasing mechanisms and

thus intensity of pain.

From the GCT perspective, the experience of pain is an

ongoing sequence of activities, largely re”exive in nature at

the outset, but modi“able even in the earliest stages by a va-

riety of excitatory and inhibitory in”uences, and by the inte-

gration of ascending and descending nervous system activity.

The process results in overt expressions communicating pain

and strategies to terminate the pain. In addition, considerable

potential for shaping of the pain experience is implied be-

cause the GCT invokes continuous interaction of multiple

systems (sensory-physiological, affect, cognition, and, ulti-

mately, behavior).

The GCT describes the integration of peripheral stimuli

with cortical states, such as anxiety, in the perception of pain.

This model contradicts the notion that pain is either somatic

or psychogenic and instead postulates that both factors have

either potentiating or moderating effects on pain perception.

In this model, for example, pain is not understood to be the

result of depression or vice versa, but rather the two are seen

as evolving simultaneously. Any signi“cant change in mood

or pain will necessarily alter the others.

The GCT•s emphasis on the modulation of inputs in the

dorsal horns and the dynamic role of the brain in pain

processes resulted in the integration of psychological vari-

ables such as past experience, attention, and other cognitive

activities into research and therapy on pain. Prior to this for-

mulation, psychological processes were largely dismissed as

reactions to pain. This new model suggested that cutting

nerves and pathways was inadequate because a host of other

factors modulated the input. Perhaps the major contribution

of the GCT was that it highlighted the central nervous system

as an essential component in pain processes and perception.

The physiological details of the GCT have been challenged,

Figure 13.2 Gate control model of pain. and it has been suggested that the model is incomplete. As

SG

A-Delta and

C-Fiber

A-Beta

Fiber

Gate Control System

Descending Influence