A common somaesthetic pathway to red nucleus and motor cortex

Comparable short latency somaesthetic responses have been observed in the red nucleus and the motor cortex. Since previous experiments showed that a ventral spinal ascending pathway could account for red nucleus responses, the present experiments were designed to establish whether the same pathway could also transmit the short latency peripheral inputs to motor cortex. Two experimental data argue in favour of a such organization: (1) Using the collision technique, it was demonstrated that somaesthetic responses recorded in red nucleus cells are transmitted by collaterals of ascending fibres ending in the ventrobasal thalamus. (2) Intracellular recordings from identified corticospinal cells were performed on cats acutely prepared on section of the brachium conjunctivum and the dorsal columns of the spinal cord. Cortico-cortical connections to motor cortex were also eliminated by lesions of the ipsilateral sensory cortex and contralateral motor cortex. With this preparation it is still possible to record postsynaptic potentials after stimulation of primary afferent fibres in the dorsal columns, caudally to their section. The existence of these somaesthetic parallel inputs to rubro- and corticospinal cells suggest that the ongoing movement might be corrected on-line by these two pathways.