Our research focuses on the mechanisms of ageing in the nervous system. An early and important discovery was that peripheral neurons, like neurons of the central nervous system, are selectively vulnerable during ageing. Certain groups of neurons exhibit loss of axons and dendrites and shrinkage of the cell soma and may eventually die, while others appear to survive into extreme old age apparently unimpaired. We describe these groups of neurons as 'vulnerable' and 'protected', respectively. Selective vulnerability, but not always of the same groups of neurons, is characteristic of the age-related neurodegenerative diseases such as Alzheimer's, Parkinson's and motor neuron disease. The causes of selective vulnerability are unknown.