A proposed natural geometry of recovery from akinesia in the lateral hypothalamic rat.
The Eshkol-Wachmann movement notation is used to analyze and describe neurological recovery from the akinesia caused by severe bilateral lateral hypothalamic (LH) damage in rats. Exploratory movement recovers along several relatively independent dimensions which appear successively. First, lateral head scanning movements recover. At about the same time or later, longitudinal (backward-forward) head scans appear. After movements along these two dimensions increase in amplitude and involve the whole body, vertical (dorsal-ventral) head scans with snout contact (along vertical surfaces) typically appear, and increase gradually in amplitude. Later, vertical rearing without snout contact emerges. Recovery proceeds cephalocaudally, as more caudal limb and body segments are recruited along each of the above dimensions separately. LH rats show delayed recruitment of caudal limb and body segments ('strait-jacket phenomenon'). Support of the body and management of limb and body segments' contact with the ground also recover relatively independently, in a proximodistal fashion. In recovery, arrests between bouts of activity become shorter. Movement first becomes organized in relation to the animals' own body, and only much later, in relation to the environment. In each sequence of movement after pronounced immobility, the rat recapitulates the process of recovery; and, any time it starts to move, it repeats the movements at a particular amplitude several times until there is an increase to the next larger size movement ('warm-up' phenomenon). These regularities explain the apparently bizarre stereotyped behavior in partial enclosures ('behavioral traps') seen in LH rats recovering from akinesia. They also explain some aspects of exploration in rats and normal social behavior of wild animals, particularly in situations involving fear and conflict.