Brain electrical activity can provide an indication of the presence or absence of consciousness, which in turn determines whether or not the animal has the capacity to suffer. The brain activity of chickens before and after hatching was monitored using an electroencephalogram (EEG). The EEGs indicated that brain activity was first apparent from day 13 of a 21-day incubation. Spectral analysis of the EEGs showed an increasing level of high frequency activity up to day 17. This activity diminished around the time of hatching before re-emerging in the newly-hatched chick (spectral analysis parameters: median frequency, 95% spectral edge frequency and total power fitted cubic regressions with F=46.77 p<0.01, F=62.48 p<0.01 and F=48.91 p<0.01 respectively). The decrease in activity may be related to neuroinhibitory effects of an oxygen shortage in the chick towards the end of incubation.

Previous studies in anaesthetised mammals have used the EEG to record responses to noxious events, which can provide further information on neurological functioning. Consciousness is needed to perceive the negative emotional component of pain. Therefore, an EEG response to noxious stimulation could indicate that the animal has the neural capacity for consciousness. Two studies were conducted to look for EEG responses to noxious stimulation in anaesthetised chickens. The results suggest that the chicken’s EEG may be less responsive to noxious events than the mammalian EEG. While a noxious electrical stimulus caused a 1.5Hz increase in median frequency 5-10 seconds after the stimulus (ANOVA and Dunnett’s test t=4.19, p<0.01), EEG parameters following the other noxious events were not significantly different from baseline (thermal, mechanical and feather-pull stimuli, ANOVA, time effect p>0.05). This discrepancy between birds and mammals may relate to differences in brain anatomy and suggests that another method may be needed to investigate the processing of noxious sensory inputs in birds.