Optical Imaging of Plastic Changes Induced by Fear Conditioning in Auditory, Visual, and Somatosensory Cortices

Second-order conditioning using light, tone and foot-shock was carried out, and conditioned responses to tone and light could be observed by monitoring the cardiac pulse. Three sensory cortical areas including auditory, somatosensory, and visual cortices in the same animal were simultaneously recorded by using optical imaging with voltage sensitive dye, RH795. Cortical activities to each stimulus including foot-shock, light, and tone were compared in naive versus conditioned animals. As a result, while only primary and secondary somatosensory cortices were activated to foot-shock alone in a naive animal, after the activation of primary and secondary somatosensory cortices, neural activities were propagated to auditory and visual cortices in conditioned animals. Our findings illustrate the integration of three different modalities through second-order conditioning. Through this integration, sensory stimulation in one modality can lead to the retrieval of associated, but presently absent sensory information in two other modalities.