Investigating the electrical response of the brain of the domestic chicken (Gallus gallus domesticus) to nociception through the use of depth electroencephalography (dEEG) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University, Manawatū, New Zealand
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Date
2015
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Massey University
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Abstract
Nociception is an unavoidable side effect of many routine management and clinical procedures
in animals. Electroencephalography (EEG) has previously been used to investigate the effect of
nociception on mammalian brain activity. This study aimed to develop a method of assessing
the avian response to nociception through depth electroencephalography (dEEG) of brain
regions believed to be involved in central pain processing. Two groups of chickens were used
in this study to investigate two brain regions, the rostral hyperpallium apicale (HA) and the
caudomedial nidopallium (NCM). These regions were chosen due to the afferent and efferent
projections they receive from the sensory thalamus and their previous implication in pain
processing. Subjects were anaesthetised, and a concentric needle electrode was inserted into
the brain to record the electrical activity in response to a number of stimuli. These stimuli
included one non-painful, somatosensory stimulus, and four nociceptive stimuli (mechanical,
thermal, feather removal and electrical). The dEEG data was then run through a spectral
analyser which generated the median frequency (F50), spectral edge frequency (F95) and total
power (PTOT). Inspection of these variables determined that within the HA there were two
populations of birds, therefore these birds were treated as separate groups in the analysis
(hHA and lHA).
It was seen that spectral characteristics of the three groups investigated differed significantly,
indicating differences in activity and function. The response to stimulation was seen to be
significantly different between these brain regions. Following stimulation, the hHA was seen to
have a significantly lower percentage of baseline spectral edge frequency and median
frequency compared to the NCM and lHA. In response to stimulation the activity of the NCM
and lHA remained constant and showed no distinguishable response, while the hHA was more
variable. The hHA was much more variable. Although there was no consistent response to
stimulation, there was a significant decrease in total power following electrical stimulation in
the hHA.
This study presents a number of interesting findings and demonstrates that different regions
of the brain respond in differing ways to stimulation. The findings suggest that the
hyperpallium apicale may respond to nociceptive stimulation, however further work is
required to distinguish this. The presence of two populations within the HA group suggests
that recordings were taken from two distinct brain regions, one of which displayed
comparatively higher sensitivity to nociceptive stimulation. Elucidation of this brain region and
further research into the response to nociception is required to further understand the
response of the avian brain to pain. For future studies, the development of more precise
methods will be required to enable more accurate recording of the activity occurring
throughout the avian brain.
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Keywords
Chickens, Physiology, Brain, Pain in animals, Pain perception, Nociceptors, Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology::Animal physiology