Rolf Hassler was a German pathologist who made important discoveries on the pathophisiology and treatment of Parkinson’s disease (PD).

In 1938 he published that autopsy of PD patients showed that while the striatum

Striatum

The striatum, also known as the neostriatum or striate nucleus, is a subcortical part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex...

 and globus pallidus

Globus pallidus

The globus pallidus also known as paleostriatum, is a sub-cortical structure of the brain. Topographically, it is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system...

 were mostly unaffected, the main affected structure was the substantia nigra pars reticulata, which loosed many neurons and also held abundant Lewy bodies. Such findings confirmed Konstantin Tretiakoff

Konstantin Tretiakoff

Konstantin Nikolaevitch Tretiakoff was a Russian neuropathologist. He was born in Fergana, Uzbekistan, as a son of military physician, who was member of Pierre Bonvalot's first Pamir expedition. He studied medicine in L'Assistance Publique des Hopitaux de Paris. He received his doctorate in 1919...

 theories, who in 1919 had reported that the substantia nigra was the main cerebral structure affected.

Hassler later was the director of the Max-Planck-Institut für Hirnforschung at Frankfurt am Main where he continued his studies on PD, becoming a pioneer in surgery for tremor.