Cold-receptor cells supply both cold- and warm-responsive projection neurons in the antennal lobe of the cockroach.

The temperature receptor cells on the cockroach antennae are all excited by rapid cooling. In the antennal lobe, however, cold- as well as warm-responsive neurons occur. They are excited either by rapid step-like cooling or rapid step-like warming. Responses to such temperature transients do not show, however, whether antennal lobe neurons convey information on slowly changing temperatures typical of temperature gradients used for orientation. In contrast slow temperature changes permit an analysis of the effects of both instantaneous temperature and its rate of change. We compared the effect of slow temperature oscillations on the responses of antennal cold-receptors cells and cold- and warm-responsive projection neurons. In all cases the discharge rates were modulated by the temperature oscillations. They displayed a double dependence on instantaneous temperature and its rate of change. Information about cooling and warming, first contained in the output of a single cold-receptor cell diverges to form the parallel pathways of cold- and warm-responsive projection neurons, thereby in particular improving the detection of fluctuations in temperature.