Distinct sensory receptors transduce thermal and mechanical energies, but we have
unified, coherent thermotactile experiences of the objects we touch. These
experiences must emerge from the interaction of thermal and tactile signals within the
nervous system. How do thermal and mechanical signals modify each other as they
interact along the pathway from skin to conscious experience? In this thesis, we study
how mechanical touch modulates cooling responses by combining psychophysics in
humans and neural recordings in rodents. For this, we developed a novel stimulator
to deliver focal, temperature-controlled cooling without touch. First, we used this
method to study in humans the sensitivity to focal cooling with and without touch. We
found that touch reduces the sensitivity to near-threshold cooling, which is perhaps
analogous to the well-established ‘gating’ of pain by touch. Second, we studied the
perceived intensity of cooling with and without touch. We found that tactile input
enhances the perceived intensity of cooling. Third, we measured the responses of the
mouse primary somatosensory cortex to cooling and mechanical stimuli using
imaging and electrophysiological methods. We found multisensory stimuli elicited
non-linear cortical responses at both the population and cellular level. Altogether, in
this thesis, we show perceptual and cortical responses to non-tactile cooling for the
first time. Based on our observations, we propose a new model to explain the
interactions between cooling and mechanical signals in the nervous system. This
thesis advances our understanding of how touch modulates cold sensations during
thermotactile stimulation
