An Extralemniscal Sensory System in the Brain

IN RECENT years it has become apparent that afferent impulses may reach the cortex by routes distinct from those involving transmission along the classic sensory pathways to the receptive areas. In 1936, Derbyshire, Rempel, Forbes, and Lambert 1 called attention to impulses evoked by sciatic stimulation which it was possible to record in areas remote from the sensorimotor strip and which had latencies much longer than did potentials confined to this region. These longer-latency potentials were called the secondary responses by Forbes and Morison, 2 as distinct from the primary responses, which had long been well known. Characteristic differences between these two distinct sensory systems aside from projection distribution and latency were elaborated by Dempsey, Morison, and Morison, 3 who presented evidence suggesting that the pathway for the secondary response might be the medial division of the medial lemniscus and that it might course more centrally before becoming widely