**3. Cross-modality dysfunction in Parkinson's disease**

Recently, a study showed that PD causes a decline in the cross-modal function of vision and olfaction [36]. This study conducted behavioral experiments to identify the influence of PD on cross-modal function by comparing the behavior of patients with PD with that of healthy controls. The principal aim of this study was to measure odor-strength perception and preference, while presenting smells paired with visual information, to characterize vision/olfaction integration in patients with PD.

In the experiment, odor detection thresholds in each participant were first determined using an olfactometer, which has five odorants (β-phenylethyl alcohol, methyl cyclopentenolone, isovaleric acid, γ-undecalactone, and skatole). For example, methyl cyclopentenolone smells like caramel pudding (pleasant) and skatole smells like rotten vegetables (unpleasant). The study employed detectable odorant thresholds in each of five categories and prepared five original pictures associated with the five odorants of each category. For example, the category "caramel pudding" consisted of a picture of "pudding" and the odorant "methyl cyclopentenolone," whereas "rotten vegetables" consisted of "rotten vegetables" and the odorant "skatole" (**Figure 4**). The "control" category consisted of a noise picture and an odorless liquid. Four combinations were arranged: the original picture with the original odorant (combination "A"), the control picture with the original odorant (combination "B"), and the original picture with the control odorant (combination "C"). A control combination was added: the control picture with the control odorant (combination "D") (**Figure 5**). Participants were asked take a sniff while viewing the picture, and were subsequently asked to evaluate the strength (weak – strong) and preference (pleasant – unpleasant) of each odor on a visual analog scale (VAS).

In the *caramel pudding* category, healthy controls overestimated the odor strength compared with patients with PD, when the original picture was presented (combinations A and C). Furthermore, healthy controls negatively estimated odor preference in combinations A and C in the "rotten vegetables" category (**Figure 6**). The results indicate that patients with PD accurately judged odor strength, without being distracted by visual appearance whereas odor strength/preference in healthy controls was influenced by visual appearance.

Furthermore, the study reported a possible effect of striatal DaT deficits in patients with PD on the olfaction-vision cross-modality. DaT imaging indicated that striatal DaT deficit in PD, especially that in the posterior putamen, is associated

#### **Figure 4.**

*Examples of the category type. Each category consists of an original odorant and an original picture corresponding to the odorant, and a control category consisting of a noise picture and an odorless liquid (this figure is cited with edit from a part of Honma et al. [36]).*

**119**

**Figure 5.**

**and olfaction**

*with edit from a part of Honma et al. [36]).*

*Cross-Modality Dysfunction between the Visual and Olfactory Systems in Parkinson's Disease*

with the cross-modal effect of perception on odor preference, and the laterality may

*Combinations of the pictures and odorants. Combination a includes the original picture and original odorant. Combination B includes the control picture and original odorant. Combination C includes the original picture and the control odorant. Combination D includes the control picture and control odorant (this figure is cited* 

**4. Possible mechanism of dysfunctional cross-modality between vision** 

Honma et al. [36] showed that the olfactory function was unaffected by visual

information in patients with PD, supporting the hypothesis that PD impairs cross-modality between vision and olfaction [36]. Healthy participants tend to

depend on the emotional category (pleasant or unpleasant) (**Figure 7**).

*DOI: http://dx.doi.org/10.5772/intechopen.90116*

*Cross-Modality Dysfunction between the Visual and Olfactory Systems in Parkinson's Disease DOI: http://dx.doi.org/10.5772/intechopen.90116*
