Place and modality analysis in nucleus of posterior commissure.

1. Single units (157) responsive to somatic stimulation in the nucleus of the posterior commissure were examined in the cat under chloralose anaesthesia. 87.3% responded to stimulation of all four limbs, 2.4% to three limbs, 8.7% to two limbs and 2% to one limb.2. 44.7% of units could be activated by phasic hair movement; 52.4% responded additionally to auditory stimuli and 34.6% to visual stimuli, although there are marked differences in degree of heterosensory convergence between hair-sensitive units and others.3. Analysis by spike numbers and latencies show marked preference for contralateral limbs.4. Results are compared with those obtained under identical experimental conditions from units of the gigantocellular bulbar reticular formation, and show that anatomically discrete areas of the reticular formation are capable of differential analysis of afferent input.