Nielsen studies the state of akinetic mutism, usually seen following gross operations in the posterior fossa. This condition has psychological relevance and interest in that it is related psychologically to catatonia, that state of apathy, or of loss of conation, characterized by immobility without loss of consciousness. Nielsen feels that the function of conation, as all cerebral functions, has a brain stem or spinal cord pattern, a diencephalic component and a cortical component. From his clinical data, including post-mortem pathological studies, he concludes that patterns of conation have a mesencephalic component about the aqueduct of Sylvius, a diencephalic component involving the mammillary bodies and the anterior thalamic nuclei, and a cortical component in the cingulate gyri.