Figure 9. Role of PTNs in the postural system stabilizing the dorsal-side-up trunk orientation in the cat.

A and B, proposed scheme for sensorimotor processing in the postural system stabilizing the dorsal-side-up trunk orientation in the cat (adapted from Deliagina et al. 2006a). A, the system consists of two subsystems, one for the shoulder girdle and the other for the hip girdle. They compensate for tilts of the anterior and posterior parts of the body, respectively (Tilt F and Tilt H). B, each subsystem includes two controllers, one for the left limb and one for the right limb. Each limb controller contains a reflex mechanism driven by somatosensory input from its own limb. These local reflexes partly compensate for tilts. The limb controllers also receive somatosensory input (direct or subjected to processing) from the opposite limbs. The motor responses to these crossed influences are added to the local reflexes. The forelimb controllers exert influences on the hindlimb controllers promoting their coordination. Reversed influences are much smaller. The PTNs constitute a part of each limb controller; they are primarily involved in the feedback control of their own limb. The corresponding sensory influences are shown by thick red lines. The PTNs are less involved in the coordination of activity between the two limbs within a girdle, and between the shoulder and hip girdles. The corresponding influences are shown by thin blue and green lines. C, role of signals from the receptive field in modulation of PTNs. Three types of PTNs are shown: 1, PTN in which the receptive field input (RF input) controls the activity both at rest and in the postural task; 2, PTN in which the receptive field input controls the activity only at rest – the activity in the postural task is controlled by a different sensory input (Non-RF input); 3, PTN in which the receptive field input is absent – the activity in the postural task is controlled by a special sensory input (Non-RF input).