Computerised infrared imaging system for studying thermal activation on the skull following somatic stimulation in small animals

A computerised infrared imaging system has been developed to measure infrared radiation as a means of functionally mapping the cerebral cortex. In two species of small mammal, rat and gerbil, the authors localised the thermal changes at the skull overlying the somatic sensory cortex following somatic stimulation of the mystacial vibrissae. Though typically small in magnitude, a thermal response could be detected through the skull. To enhance detection sensitivity, a number of measures were taken to improve various aspects of data acquisition, stimulus delivery and control of experimental conditions. Regarding data analysis, a coordinate system based on skull landmarks was adopted to localise thermally-active regions for comparison across animals of the same species. To extract the region of weak temperature changes, a coarse-to-fine detection strategy was developed, which searched automatically for clusters of temporally- and spatially-corrected pixels above a data-driven threshold. Thus, the dynamic aspect of the thermal changes at any region of interest on the skull could be studied efficiently. The detection algorithm was tested against simulated responses in addition to empirical data obtained from animals. All of the above software was integrated in a user-friendly package.