Rene Descartes, in the seventeenth century, put the topic of human nature on a less unmanageable basis. The first big problem with Descartes' proposal is the difficulty of imagining how something lacking 'extension' could interact with the material world. Modern neuroscientists should take warning from the fact that evidence apparently supporting his fudge is easy to find. People who are losing their minds, due to Alzheimer's, often have calcified pineal glands and it would have been natural for a seventeenth-century anatomist to conclude that the connection between cogitans and extensa must be getting blocked by the calcification in these cases. Pineal glands tend to calcify with age and there's no direct correlation with dementia. Nevertheless similar false inferences quite appear in the scientific literature, especially in connection with brain-scan. A better reason for scepticism is down to the first of the main problems with Descartes' res cogitans; namely that of envisaging how it could possibly interact with the material world.