Basic research helps to understand clinical knowledge which in turn leads to new fundamental research. Two examples are taken from the studies of the anomalies existing in the brain of patients suffering from Parkinson disease or deafferentation Pain. The researches performed to solve these two problems for the past 40 years (in particular by the author's working group) are replaced in the international context. In Man the precision of stereotaxic technique was improved by using the organisation of the somato-sensory thalamic projection described in animals by the physiologists. In the thalamus of Parkinsonian patients, the presence of cells bursting at tremor frequency led to search for the relations existing between the striato-nigral system and the motor thalamus. In the patients suffering from deafferentation Pain, a special role is attributed to the medial thalamus, whose characteristics were formerly studied in animals. The origin of the deafferentation Pain is nowadays studied in an animal model of this disease.