Mm Merzenich

Regional segregation of neurons responding to quickly adapting, slowly adapting, deep and Pacinian receptors within thalamic ventroposterior lateral and ventroposterior inferior nuclei in the squirrel monkey (Saimiri sciureus).

Abstract The ventroposterior nuclei and the ventroposterior inferior nucleus of the thalamus were mapped in squirrel monkeys ( Saimiri sciureus ) using low-impedance platinum-iridium microelectrodes. The body site and receptor category from which the optimum response was obtained was recorded every 50 μm in orthogonal penetrations through these nuclei. The results suggest that the neurons are grouped according to submodality in this area and that discrete and spatially separate volumes of the thalamus are devoted to input from deep, Pacinian, cutaneous rapidly adapting and cutaneous slowly adapting receptors. The Pacinian responses were limited to the ventroposterior inferior nucleus and deep responses were limited to a region just above the ventroposterior nuclei. Within ventroposterior nuclei the cutaneous rapidly adapting and cutaneous slowly adapting volumes were interspersed in a pattern that could not be readily defined. The results indicate that there is more than one representation of the body in this area of the thalamus. Discontinuities in receptive field sequences make it difficult to see how any representation can be a spatially continuous map of the body.

Effects of sensorimotor restriction and anoxia on gait and motor cortex organization: Implications for a rodent model of cerebral palsy

Chronic or acute perinatal asphyxia (PA) has been correlated with the subsequent development of cerebral palsy (CP), a developmental neurological disorder characterized by spasticity and motor abnormalities often associated with cognitive deficits. Despite the prevalence of CP, an animal model that mimics the lifetime hypertonic motor deficits is still not available. In the present study, the consequences of PA on motor behavior, gait and organization of the primary motor cortex were examined in rats, and compared with the behavioral and neurological consequences of early postnatal movement-restriction with or without oxygen deprivation. Rats subjected to PA had mild increases in muscular tone accompanied by subtle differences in walking patterns, paralleled by significantly altered but relatively modest disorganization of their primary motor cortices. Movement-restricted rats, suffering PA or not, had reduced body growth rate, markedly increased muscular tone at rest and with active flexion and extension around movement-restricted joints that resulted in abnormal walking patterns and in a profoundly distorted representation of the hind limbs in the primary motor cortex. Within the sensorimotor-restricted groups, non-anoxic rats presented the most abnormal pattern and the greatest cortical representational degradation. This outcome further supports the argument that PA per se may represent a substrate for subtle altered motor behaviors, and that PA alone is sufficient to alter the organization of the primary motor cortex. At the same time, they also show that early experience-dependent movements play a crucial role in shaping normal behavioral motor abilities, and can make a powerful contribution to the genesis of aberrant movement abilities.