Decorticate Rigidity.

Abstract

On section of the brain stem at the level of the colliculi, Sherrington 1 in 1897 observed that the animals (cats) passed into a condition of increased extensor tonus. This condition he called “decerebrate rigidity”. The rigidity was “confined to those muscles which maintain the animal in erect attitude”.

Goltz, 2 Holmes, 3 Rothman 4 and de Barenne 5 studied dogs in which the frontal portion of the brain was removed, and in which most of the thalamus and midbrain were left intact, but reported no rigidity. Thiele 6 and Magnus 7 have stated that it is necessary to section the brain in the mesencephalic region to obtain rigidity. Hence it has been generally accepted that the condition results, not from removal of the cerebral cortex, but from transection in the region of the midbrain, at or near a supposed rigidity center. However, we find that rigidity follows at once if a sufficient amount of the cortex alone is removed, leaving all other structures intact.

In our experiments four monkeys (Javanese macaques), and three dogs have been used. After removal of the calvarium, as much of the cortex was clipped off with scissors as could be reached without injury to other portions of the brain. The plane of removal was sufficiently superficial so that the portions of cortex surrounding the deep sulci were left intact. The areas of removal were in general as follows : dorsal, medial and lateral surfaces and the anterior tips of the frontal cortices, all of the parietal cortices, the posterior portion of the temporal lobes, and all of the occipital cortices, except that in contact with the anterior half of the tentorium. In every case a well marked generalized muscular rigidity appeared during recovery from the anesthesia, and the nervous responses retained were apparently entirely automatic.