after being exposed to a warm stimulus, and would present the animal with afterimages even after the stimulus was removed. Neuroanatomy In all cases, the facial pit is innervated by the trigeminal nerve. In crotalines, information from the pit organ is relayed to the nucleus reticularus caloris in the medulla via the lateral descending trigeminal tract. From there, it is relayed to the contralateral optic tectum. In boas and pythons, information from the labial pit is sent directly to the contralateral optic tectum via the lateral descending trigeminal tract, bypassing the nucleus reticularus caloris. It is the optic tectum of the brain which eventually processes these infrared cues. This portion of the brain receives other sensory information as well, most notably optic stimulation, but also motor, proprioceptive and auditory. Some neurons in the tectum respond to visual or infrared stimulation alone; others respond more strongly to combined visual and infrared stimulation, and still others respond only to a combination of visual and infrared. Some neurons appear to be tuned to detect movement in one direction. It has been found that the snake's visual and infrared maps of the world are overlaid in the optic tectum. This combined information is relayed via the tectum to the forebrain. The nerve fibers in the pit organ are constantly firing at a very low rate. Objects that are within a neutral temperature range do not change the rate of firing; the neutral range is determined by the average thermal radiation of all objects in the receptive field of the organ. The thermal radiation above a given threshold causes an increase in the temperature of the nerve fiber, resulting in stimulation of the nerve and subsequent firing, with increased temperature resulting in increased firing rate. The sensitivity of the nerve fibers is estimated to be >0.001 °C. The pit organ will adapt to a repeated stimulus; if an adapted stimulus is removed, there will be a fluctuation in the opposite direction. For example, if a warm object is placed in front of the snake, the organ will increase in firing rate at first, but after a while will adapt to the warm object and the firing rate of the nerves in the pit organ will return to normal. If that warm object is then removed, the pit organ will now register the space that it used to occupy as being colder, and as such the