He was training as a neurologist at Groningen when he gave it up to move to Baltimore as assistant professor in the Department of Anatomy at the University of Maryland School of Medicine.
[4] He was elected a Fellow of the Royal Society in 1986, his candidature citation reading "Distinguished for his microanatomical mapping of the neuronal networks which interconnect particular areas of the neocortex with one another and with the thalamus, brainstem and spinal cord, especially in primates.
His studies have involved the correlation of focal lesions in the brain with subtle disorders of motor performance, previously undetected but now exposed and analysed in ingenious behavioural experiments.
He has made adventurous use of new microanatomical methods, invented or improved by himself, in order to examine descending pathways in the brainstem, such as the double labelling of cortical neurones by fluorescent dyes with different excitation wavelengths and chemical affinities, transported by axoplasmic flow in a retrograde direction from separately injected termini.
The discoveries thus made through a powerful combination of complementary techniques have stimulated much behavioural and micro-physiological experimentation in his own and other laboratories".