| In order to view the world in a unified manner, information from the different senses must combine at some point in the sensory stream. This is known as perceptual binding and has led to the study of how various senses interact, termed multisensory integration. An intriguing example of a crossmodal interaction is the finding from various imaging studies that primary visual cortex is activated while subjects performed purely olfactory tasks. This is in line with the literature documenting a connection between vision and olfaction, but whether visual cortical activity and olfactory perception are connected causally is unknown. In this thesis I will investigate the connection between vision and olfaction using Transcranial Magnetic Stimulation (TMS). TMS is a non-invasive method of stimulating cortex via magnetic induction. The present research involved the application of TMS to early visual cortex, including V1, bilaterally in the context of experiments that test both visual and olfactory perception. In particular subjects were tested on a visual task (contrast detection) and two olfactory tasks that probe the ability to discriminate odor intensity and quality. Behavioral experiments were carried out before and after the application of either no TMS, real TMS to V1, sham TMS to V1 (replicates experimental conditions of real TMS but no current is produced in the cortex) and real TMS to primary auditory cortex. The results have revealed a significant improvement in performance on the visual task, replicating previous data. Interestingly, improvements in the ability of subjects to discriminate among odor qualities following TMS of V1 were also found, with a tendency for female subjects to show more improvement than their male counterparts. Similar improvements were not found in the ability to discriminate among odor intensities or on either olfactory task in any of the control conditions (no TMS or sham TMS or auditory cortex TMS). Implications and limitations of the present results are discussed. |
