Interchangeable Role of Motor Cortex and Reafference for the Stable Execution of an Orofacial Action

Animals interact with their environment through mechanically active, mobile sensors. The efficient use of these sensory organs implies the ability to track their position; otherwise, perceptual stability or prehension would be profoundly impeded. The nervous system may keep track of the position of a sensorimotor organ via two complementary feedback mechanisms-peripheral reafference (external, sensory feedback) and efference copy (internal feedback). Yet, the potential contributions of these mechanisms remain largely unexplored. By training male rats to place one of their vibrissae within a predetermined angular range without contact, a task that depends on knowledge of vibrissa position relative to their face, we found that peripheral reafference is not required. The presence of motor cortex is not required either, except in the absence of peripheral reafference to maintain motor stability. Finally, the red nucleus, which receives descending inputs from motor cortex and cerebellum and projects to facial motoneurons, is critically involved in the execution of the vibrissa positioning task. All told, our results point toward the existence of an internal model that requires either peripheral reafference or motor cortex to optimally drive voluntary motion.SIGNIFICANCE STATEMENT How does an animal know where a mechanically active, mobile sensor lies relative to its body? We address this basic question in sensorimotor integration using the motion of the vibrissae in rats. We show that rats can learn to reliably position their vibrissae in the absence of sensory feedback or in the absence of motor cortex. Yet, when both sensory feedback and motor cortex are absent, motor precision is degraded. This suggests the existence of an internal model able to operate in closed- and open-loop modes, requiring either motor cortex or sensory feedback to maintain motor stability.

Primary nonurachal adenocarcinoma in the bilharzial urinary bladder: deoxyribonucleic acid flow cytometric and morphologic characterization in 93 cases

OBJECTIVES

To characterize adenocarcinomas of the urinary bladder by their DNA profiles and their proliferative properties.

METHODS

Primary nonurachal adenocarcinomas, found in 93 patients with bilharzial bladder carcinomas, were studied using DNA flow cytometry. Tumor ploidy and S-phase fraction were related to tumor grade, stage, cell type, and lymph node status.

RESULTS

Aneuploidy with high S-phase fractions, found in 90% of the tumors, demonstrates the high malignancy potential of these tumors, the majority of which were found to be muscle-infiltrative. There were no relationships between ploidy or S-phase fraction and tumor grade and stage. Lymph node metastases, present in 24% of the 93 patients, were found exclusively in nontetraploid aneuploid tumors with high S-phase fractions exceeding 100%. Paraffin-embedded tissues compared with fresh material gave the same information on ploidy, whereas bladder washing did not provide adequate information.

CONCLUSIONS

The high aggressiveness of adenocarcinomas in the biharzial bladder is confirmed and can be explained by their proneness to develop gross chromosomal aberrations combined with high cell proliferation.