Behavioural and neural correlates of mental imagery in sheep using face recognition paradigms

Determining objective measures for proof of consciousness in non-human animals has been helped by improved understanding of neural correlates of human consciousness. Functional imaging and neuropsychological studies have shown remarkable overlap between structures involved in actual perception of social and non-social objects and those involved in forming mental images of them. One area of particular interest is individual face recognition. This involves regions of the temporal lobe that are mainly only activated by actual perception or mental imagery effaces. Using behavioural, neuroanatomical and neurophysiological approaches in sheep, we have found that they have similar specialized abilities for recognizing many individuals from their faces. They have developed the same specialized neural processing regions in the temporal lobe for aiding such recognition. Furthermore, parallel activation of other brain regions controlling behavioural and emotional responses only occurs when they are overtly interested in the individuals whose faces they perceive. Such interest might therefore equate to their becoming consciously aware of them. Preliminary experiments have indicated that sheep may form and use mental images and that the regions of the temporal lobe that respond to faces can also do so under conditions where faces are suggested but do not actually appear. Such similarities between humans and sheep in this form of social recognition make it difficult to claim that humans can form mental images effaces whereas sheep cannot. While the ability to form and use mental imagery is not in itself definitive proof of consciousness, it is an important component part.