The lateral cervical nucleus (LCN) was investigated with extracellular recordings in the anesthetized cat. A total of 556 LCN units were characterized; the locations of most of these were histologically verified. Half of these had receptive fields on the rostral third of the ipsilateral body surface including the face; 14% had fields on the thorax or abdomen, 33% had fields on the hindlimb or tail, and about 3% had receptive fields larger than one limb. 2. The LCN was observed to be somatotopically organized in experiments using angled microelectrode penetrations. Hindlimb units were dorsolateral, forelimb units ventromedial, and face units most medial within the LCN. In regions where LCN cells were present only in the medial portion of the dorsolateral funiculus, they were all forelimb units. 3. A special subpopulation (17%) of cells were clustered most ventromedially in the LCN. These units had large or disjoint receptive fields, and/or responded to deep, visceral, or noxious stimulation. A third of these did not project in the medial lemniscus (ML); many were synaptically activated by stimulation of the ML. Those that did project in the ML had significantly longer latencies than all other LCN units. It is suggested that this subpopulation contains local LCN interneurons. 4. The specific mechanoreceptor inputs were identified for each of 121 projecting LCN units. Receptor inputs were uniform across each receptive field; that is, each unit that responded to a given receptor type was observed to respond to receptors of that type throughout its receptive field. Input from large-fiber-diameter, velocity-sensitive mechanoreceptors was predominant. The absence of input from slowly adapting type I and II receptors and from joint receptors was confirmed. A significant number of units (17.3%) could be driven by only one receptor type. The LCN sample profile agrees closely with the receptor representation in the hindlimb portion of the spinocervical tract. It is concluded that these data that anatomic specification of convergence occurs in the LCN with respect to receptor connectivity, and that this specification originates in lamina IV of the dorsal horn. 5. Stimulation of the dorsal column nuclei synaptically excited 23% of the LCN units tested. In two cases it was possible to demonstrate, by collision, that this occurred via collaterals of spinocervical tract axons. It is concluded that some spinocervical axons have collaterals terminating in the rostral parts of the dorsal column nuclei.
