Infrared Imaging in Pit Vipers and Pythons: From Biology to Technology?

Dr. Michael Grace

Pit vipers, pythons and boas possess infrared-sensitive pit organs that are part of an elaborate neural system allowing high sensitivity detection of infrared radiation, and the formation of infrared-based images in the brain.  Information from the eyes and the pit organs ultimately converge in the optic tectum of the brain, effectively allowing these snakes to “see” simultaneously using two distinct regions of the electromagnetic spectrum.  Together, infrared imaging and vision provide accurate and precise guidance of complex behavior including the generation of predatory and/or defensive strikes under a variety of environmental conditions.  We are using a variety of methods to develop a better understanding of high-sensitivity infrared imaging with the ultimate goal of providing new information for the development of novel artificial infrared sensors.  Our behavioral results show that infrared imaging system is fundamentally a contrast detector (like vision), though the behavioral correlates of infrared imaging and vision are significantly different.  Further, while snakes may use infrared imaging and vision simultaneously, infrared-imaging snakes make accurate and precise predatory strikes under conditions of either very low visual contrast or complete blindness, demonstrating that infrared imaging is a stand-alone system.  We are also using micro structural and histochemical analyses to understand the nature of infrared absorption in the pit organ.  We discovered regular and characteristic arrays of epidermal surface nanopits in pit organs; we have hypothesized that these may function as a spectral filter, enhancing IR photon absorption while scattering visible light.  While we know little about the mechanism of infrared signal transduction, our immunocytochemical analyses show that infrared receptors are not modified photoreceptors, and have identified candidate proteins involved in infrared absorption, signal amplification, and/or adaptation.