Disorders of higher mental function due to single infarctions in the thalamus and in the area of the thalamofrontal tracts.

Nine patients (five female and four male, mean age 58 years) with small infarcts in the thalamus (TH) or in the region of the thalamofrontal tracts and producing acute mental disturbances which in the acute phase of insult consisted of dementia in seven cases and mild cognitive disturbances in two cases. The complex of mental changes was similar to that seen in "frontal syndrome" and was characterized largely by lack of spontaneity, adynamia, disorientation, loss of attention and memory, slowing of all mental processes, and lack of criticality and adequacy. Accompanying focal neurological symptoms were mild in seven patients and moderate or pronounced in two. In five patients, the severity of mental disturbances decreased with time. Computer tomography demonstrated small infarcts in the anterior or medial parts of the TH in seven patients and in the posteromedial parts of the anterior limb of the internal capsule, i.e., the thalamofrontal tracts, in two cases. In five cases, infarcts were located in the dominant hemisphere, with lesions in the non-dominant hemisphere in three and in both hemispheres in one. The positions of all foci corresponded to structures traversed by pathways connecting the TH and the lower part of the reticular formation to the frontal lobes. It is suggested that disconnection of these pathways leads to cognitive lesions or dementia because of functional inactivation of the frontal cortex.