Hypermetria in forelimb target-reaching after interruption of the inhibitory pathway from forelimb afferents to C3-C4 propriospinal neurones.

Forelimb target-reaching in cats with a transection at C5/6 of the cortico- and rubrospinal tracts is known to depend on C3-C4 propriospinal neurones (PNs). An additional lesion transecting the dorsal column (DC) in C5/6, caudal to the C3-C4 PNs, gave pronounced hypermetria in lifting and protraction during target-reaching. If the additional DC lesion instead was made in C2, rostral to the C3-C4 PNs, there was only small hypermetria in lifting and none in protraction. It is postulated that the hypermetria after the C5/6 DC lesion is due to interruption of the inhibitory pathway from the forelimb to the C3-C4 PNs. It is suggested that feedback control from the forelimb of the premotoneurones is an integral part of the control of normal target-reaching.