Reticulospinal neurons were identified by antidromic invasion from spinal cord electrodes chronically implanted at C4 in cats. 2. Most of the neuronal population studied lay within the medial portion of the giant cell field from the anterior pontine and to the anterior medullary reticular formation (FTG). A few cells were found in the tegmental reticular nucleus (TRC) which has not previously been known to project to the spinal cord. 3. Extracellular action potentials from the neuronal somata of the identified neurons were recorded continuously throughout naturally occurring sleep-waking cycles. 4. The identified reticulospinal neurons shared three properties, suggesting a generator function in desynchronized sleep (D) (with previously recorded but unidentified FTG neurons): selectivity (or concentration of discharge in D); tonic latency (or firing rate increases beginning several minutes prior to D); and phasic latency (or firing rate increases occurring prior to eye movements within D). 5. The location, discharge properties, and spinal projections of FTG neurons are, thus, all consistent with the hypothesis that they may directly mediate some of the descending excitatory and inhibitory influences on spinal reflex pathways in desynchronized sleep.
