Distal forelimb representations in primary motor cortex are redistributed after forelimb restriction: a longitudinal study in adult squirrel monkeys.

Primary motor cortex (M1) movement representations reflect acquired motor skills. Representations of muscles and joints used in a skilled task expand. However, it is unknown whether motor restriction in healthy individuals results in complementary reductions in M1 representations. With the use of intracortical microstimulation techniques in squirrel monkeys, detailed maps of movement representations in M1 were derived before and up to 35 wk after restriction of the preferred distal forelimb (DFL) by use of a soft cast. Although total DFL area and movement threshold remained constant, casting resulted in a redistribution of digit and wrist/forearm representations. Digit representations progressively decreased, whereas wrist/forearm representations progressively increased in areal extent. In three of four monkeys, hand preference returned to normal by the end of the postcast recovery period, and postrecovery maps demonstrated reversal of restriction-induced changes. However, in one monkey, a chronic motor impairment occurred in the casted limb. Rehabilitation via a forced-use paradigm resulted in recovery in use and skill of the impaired limb, as well as restoration of normal motor maps. These results demonstrate that plasticity in motor representations can be induced by training or restricting movements of the limb. Physiological changes induced by restriction appear to be reversible, even in the case of adverse motor outcomes. The respective contributions of both disuse and lost motor skills are discussed. These results have relevance for clinical conditions requiring forelimb casting as well as interpreting the differential effects of injury and disuse that are necessarily intertwined after cortical injury, as occurs in stroke.

Reach and posture hand preferences during arboreal feeding in Sifakas (Propithecus sp.): a test of the postural origins theory of behavioral lateralization.

Sixteen sifakas (11 Propithecus verreauxi coquereli, 2 Propithecus verreauxi verreauxi form majori, and 3 Propithecus tattersalli) were videotaped as they fed on leaves in an arboreal context. The hand used to feed and the hand used to maintain postural stability was coded. For each subject, the lateral bias of the hand used to feed was opposite the hand used in postural support. Seven sifakas displayed no bias for feeding or posture-related hand use, 7 sifakas displayed significant feeding-related reach preferences for pulling branches to the mouth (5 left- and 2 right-hand preferences), and 9 sifakas exhibited significant hand preferences for postural support (2 left-, 7 right-hand preferent). Although these data do not strongly support the postural origins theory of behavioral lateralization, the modal preference pattern for sifakas that displayed significant hand preferences for posture and feeding involve a left bias for feeding and a right bias for postural support. s reserved).

Patterns of hand and mouth lateral biases in bamboo leaf shoot feeding and simple food reaching in the gentle lemur (Hapalemur griseus).

Lateralized feeding behaviors of 7 wild-born and 6 captive-born Hapalemur griseus sp. were evaluated in two conditions, simple food reaching and species-typical bamboo foraging. Gentle lemurs were found to have the strongest lateral hand preference in simple food reaching of any prosimian species yet studied. However in this small sample, population-level lateralization was not found: 5 preferred the right hand and 8 the left. The movement pattern used by hapalemurs when feeding on bamboo leaf shoots was categorized into four components: PULL IN, COUNTERFORCE, TURN, and FEED IN. Lateral hand bias was scored for all four components and lateral mouth preference was scored for the two components that involved the mouth (COUNTERFORCE and FEED IN). Strong positive correlations were found between hand preference in the most lateralized components of shoot eating (TURN and FEED IN) and simple food reaching. This suggests that the gentle lemurs' species-typical bamboo feeding behavior may contribute to the exceptionally strong hand preference for simple food reaching seen in this species. There were negative correlations between the component measure of shoot feeding that required strength (COUNTERFORCE) and the components that required manipulation (TURN and FEED IN). Within the COUNTERFORCE and FEED IN components, mouth preference and hand preference were positively associated in a manner that suggested one side of the mouth was preferred for removing the shoot and the other side for mastication. Asymmetrical dental wear may provide a means of dating behavioral lateralization in ancestral species. © 1993 Wiley-Liss, Inc.