Quantitative Sensory Testing (QST) - Does assessing ... - TI Pharma

1. General introduction
Aristotle (384 to 322 BC) (Fig.1-1), the great Greek
philosopher, was the first to describe “sense”. He described
five senses: sight, hearing, taste, smell, and touch. For
Aristotle, the brain had no function in sensory processing.
The sensorium commune, or center of sensory perception,
was located in the heart, which he considered the center
of all the fundamental life functions and the location of
the soul. He contemplated the function of the brain to be
limited to the production of cool secretions that cooled the
hot air and blood arising from the heart. For him, an excess
of vital heat in combination with an increased sensitivity
to sensations, in particular touch, was responsible for the
“emotion” pain (Bonica 1991).
Figure 1-1: Picture of
Aristotle
From: biography4u.com
Today we still believe there are five senses including touch. Arrays of receptors such as
Pacinian and Meissner corpuscles, Merkel’s disks and Ruffini endings sense different
aspects of touch throughout our bodies. They are tuned to different aspects of the
somatosensory world – touch, temperature and body position - with yet others for the
sensations of pain. Although often classed with touch, pain is actually a phenomenon
serving different functions and involves a different anatomical organisation.We
recognise peripheral nerves, the spinal cord and the brain as major structures involved
in the perception and interpretation of painful sensory information. The interplay of
sensory information within these structures is not only relevant for the perception of
pain per se but it also enables pain to serve a biologically important protective function.
In this context, the sensation of pain is a normal response to injury or disease and
induces withdraw from potentially damaging situations and protects a damaged body
part while it heals.
In the last few decades basic research brought detailed understanding of concepts and
theories regarding pain mechanisms. In 1965, Pat Wall and Ron Melzack published
their paper in Science, entitled a ‘New Theory of Pain’ (Melzack & Wall 1965). The gate
control theory stated that the transmission of pain from the peripheral nerve through
the spinal cord was subject to modulation by both intrinsic neurons and controls from
the brain. This theory explains how the central nervous system deals with sensory
inputs but does not emphasise peripheral processes. In the peripheral nervous system
there are three main types of sensory fibres involved in the sensory experience, Aβfibres,
Aδ-fibres, and C-fibres (Fig. 1-2). Aβ-fibres are large in diameter and highly
myelinated, allowing a fast conduction of action potentials. These fibres have low
activation thresholds and normally respond to light touch. Aδ-fibres are smaller in
diameter and thinly myelinated, and therefore slower-conducting than Aβ-fibres. Aδfibres
have higher activation thresholds and respond to both thermal and mechanical