Helmut Segner Fish Nociception and pain A biological perspective

pathways are ultimately converging on the same subcortical and
limbic structures that are directly accessed by ascending spinal
pathways (Price 2000). The few examples may illustrate that
the generation of pain is anything else than a linear translation
of a nociceptive signal into pain sensation, but results from a
complex crosstalk between different regions in cortex, subcortex
and brainstem. There is general agreement that the extent to
which a pain stimulus is experienced as an affective or emotive
state depends upon parallel and serial activities in different
areas of the pain matrix (Tracey 2005). Nociceptive input is
rapidly conveyed to multiple brain regions that collectively, as
a circuit, are capable of processing the input. The fact that pain
perception is an integrated brain activity is undisputed, only the
relative importance of specific regions or pathways is subject of
on going discussions. For instance, while Pessoa and Adolphs
(2010, 2011) emphasize the importance of cortical activities, de
Gelder et al. (2011) point to the essential role of subcortical regions.
Both groups, however, do not claim that pain perception
takes place either in cortex or subcortex, but they emphasize
the idea of the pain matrix.
3. Nociception and pain perception in fish
When studying pain in animals, a principal obstacle is that we
have no direct access to their subjective experience and feelings.
While we still can record the sensing of environmental stimuli,
the feelings and emotions possibly associated with the sensing the
stimuli have to be deduced from the presence and/or response
of operational indicators of the emotional states. Typically, parameters
which connect in an identifiable and defined way with pain
perception in man are used as operational indicators, and these
indicators are then studied in animals in order to infer from their
presence or absence on the capability of pain perception in the
animal under study (Bateson 1991, Rose 2007, Cottee 2012). Rose
(2007) provides an illustrative example of this approach:
“Stress in man is characterized by an elevation of plasma cortisol
levels. Thus, stress may be operationally defined as ‘elevation of
plasma cortisol levels’. If an animal in a stressful situation shows
an increase of plasma cortisol levels, we infer that this animal experiences
stress, in reference to what we know from man. In the
case of cortisol and stress, it is easy to accept that ‘cortisol’ is a
valid operational indicator of ‘stress’; however, it is much more
problematic to identify a valid operational indicator for complex
cognitive properties and emotive states such as ‘feeling of pain’.”
The problem may be exemplified by the controversial discussion
on the role of the neocortex for an animal’s capability to sense
pain. In man, the neocortex is of central importance for conscious
pain perception. Therefore, presence or absence of the neocortex
may be taken as indicator for the capability of pain perception in
an animal.
Following this line of thinking, only mammals would be able
to experience pain. Indeed, the fact that fish lack a neocortex (see
30 Fish. Nociception and pain | Contributions to Ethics and Biotechnology
Fish. Nociception and pain | Contributions to Ethics and Biotechnology
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