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

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

#### **Figure 6.**

*(A) Strength of the odor represented on the visual analog scale. (B) Preference for odor on the visual analog scale. The visual analog scale scores of the groups (healthy controls and participants with PD) and combinations (A, B, and C) were compared for each category. The control category (combination D) was analyzed independently. Asterisks indicate significant differences. These results show that the visual input affects odor estimation in healthy controls, with little effect in PD (this figure is cited with edit from a part of Honma et al. [36]).*

overestimate odor when presented with an original picture, for example, a picture of *caramel pudding* without the methyl cyclopentenolone odorant, will be perceived as pleasant. In contrast, patients with PD tend to concentrate more on smell, rather than the influence of visual stimuli. The odor estimate is independent of vision in patients with PD.

**121**

**Figure 7.**

areas, such as the ENT and PIR.

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

Olfactory perception is ambiguous, and a smell may be hard to identify without verbal or visual assistance. It is true that olfaction is modulated by visual elements [7, 8]. This multimodal integration is responsible for the OFC, which receives information from visual association, and the olfactory, gustatory, somatosensory and, auditory areas [37]. Recent brain imaging studies showed that the OFC

*Regression analysis identified the left posterior putamen as the independent variable for the cross-modal effects of pleasant categories (caramel pudding, fresh roses, and canned peaches). The right posterior putamen was identified as the independent variable for the cross-modal effects of unpleasant categories (rotten vegetables* 

*and dirty socks). The laterality in putamen may depend on emotionality.*

participates in vision-olfaction integration in healthy individuals [7]. Gottfried and Dolan (2003) noted higher activation of the OFC when a smell is presented with a word label [7]. Cognitive factors, such as visual stimuli modulate representations of odor at a relatively early level of cortical processing, known as the top-down cognitive influence, which directly affects emotion [38]. Healthy participants exhibited dominance of the visual sense in this study. On the other hand, patients with PD exhibited decrease dominance of visual information. They concentrated more on olfactory perception, without modulation from visual input. The OFC in patients with PD is known to be less active for all modalities during stimulation, including olfaction [39]. Decreased activation of the OFC in patients with PD may partly account for declining cross-modality. Moreover, detection and cognition levels for odor were lower than those in the controls. During olfaction, the OFC also integrates information from the AMG and HI, which play a role in emotional evaluation and memory retrieval [37]. Reduction of OFC function may lead to deficits in recognition and identification of odor. Thus, patients with PD may tend to focus more on smell detection, which may need activation of the basic primary olfactory

The relationship of DaT levels in PD with odor preferences demonstrated by the study is significant. However, it has been reported that administration of dopamine agonists (levodopa) does not influence the olfactory deficit. Thus, dopamine loss may not affect olfaction [40]. Here, it was not possible to establish a direct link between olfaction and dopamine levels, as measured by DaT in the putamen. However, earlier findings suggest that the putamen may play a role in sensory integration [34, 35]. Lack of dopamine linked to deficient DaT protein in the striatum leads to a decline in dopamine levels in several regions [41]. The corticostriatal loop sends signals that pass through brain regions, such as the striatum–pallidus–thalamic–cortex [42]. Dopamine regulates the prefrontal-AMG circuit, which plays an important role in emotion processing [43]. This suggests that vision-olfaction integration may be influenced by dopamine signals, via a striatum-centered network.

*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*

#### **Figure 7.**

*Sino-Nasal and Olfactory System Disorders*

**120**

**Figure 6.**

patients with PD.

*Honma et al. [36]).*

overestimate odor when presented with an original picture, for example, a picture of *caramel pudding* without the methyl cyclopentenolone odorant, will be perceived as pleasant. In contrast, patients with PD tend to concentrate more on smell, rather than the influence of visual stimuli. The odor estimate is independent of vision in

*(A) Strength of the odor represented on the visual analog scale. (B) Preference for odor on the visual analog scale. The visual analog scale scores of the groups (healthy controls and participants with PD) and combinations (A, B, and C) were compared for each category. The control category (combination D) was analyzed independently. Asterisks indicate significant differences. These results show that the visual input affects odor estimation in healthy controls, with little effect in PD (this figure is cited with edit from a part of* 

*Regression analysis identified the left posterior putamen as the independent variable for the cross-modal effects of pleasant categories (caramel pudding, fresh roses, and canned peaches). The right posterior putamen was identified as the independent variable for the cross-modal effects of unpleasant categories (rotten vegetables and dirty socks). The laterality in putamen may depend on emotionality.*

Olfactory perception is ambiguous, and a smell may be hard to identify without verbal or visual assistance. It is true that olfaction is modulated by visual elements [7, 8]. This multimodal integration is responsible for the OFC, which receives information from visual association, and the olfactory, gustatory, somatosensory and, auditory areas [37]. Recent brain imaging studies showed that the OFC participates in vision-olfaction integration in healthy individuals [7]. Gottfried and Dolan (2003) noted higher activation of the OFC when a smell is presented with a word label [7]. Cognitive factors, such as visual stimuli modulate representations of odor at a relatively early level of cortical processing, known as the top-down cognitive influence, which directly affects emotion [38]. Healthy participants exhibited dominance of the visual sense in this study. On the other hand, patients with PD exhibited decrease dominance of visual information. They concentrated more on olfactory perception, without modulation from visual input. The OFC in patients with PD is known to be less active for all modalities during stimulation, including olfaction [39]. Decreased activation of the OFC in patients with PD may partly account for declining cross-modality. Moreover, detection and cognition levels for odor were lower than those in the controls. During olfaction, the OFC also integrates information from the AMG and HI, which play a role in emotional evaluation and memory retrieval [37]. Reduction of OFC function may lead to deficits in recognition and identification of odor. Thus, patients with PD may tend to focus more on smell detection, which may need activation of the basic primary olfactory areas, such as the ENT and PIR.

The relationship of DaT levels in PD with odor preferences demonstrated by the study is significant. However, it has been reported that administration of dopamine agonists (levodopa) does not influence the olfactory deficit. Thus, dopamine loss may not affect olfaction [40]. Here, it was not possible to establish a direct link between olfaction and dopamine levels, as measured by DaT in the putamen. However, earlier findings suggest that the putamen may play a role in sensory integration [34, 35]. Lack of dopamine linked to deficient DaT protein in the striatum leads to a decline in dopamine levels in several regions [41]. The corticostriatal loop sends signals that pass through brain regions, such as the striatum–pallidus–thalamic–cortex [42]. Dopamine regulates the prefrontal-AMG circuit, which plays an important role in emotion processing [43]. This suggests that vision-olfaction integration may be influenced by dopamine signals, via a striatum-centered network.

Dopamine deficiency in PD may affect vision-olfaction integration, including emotion and cognitive processing.

The laterality of DaT level in the putamen related to odor preference is of further interest. That is, the left is associated with pleasant smells and the right is associated with unpleasant smells. A recent study has shown that a pleasant odor is associated with bilateral or left AMG activation, and an unpleasant odor is associated with activation of the right AMG [27]. The left/right difference for smell-evoked emotion may be linked to AMG processing, because these regions are strongly connected at a fiber level [44].
