Implicit olfactory processing attenuates motor disturbances in idiopathic Parkinson’s disease

Many reports in the literature indicate that idiopathic Parkinson's disease (IPD) patients have substantial olfactory dysfunctions even before motor symptoms become evident. It has not yet been clarified, however, if some form of implicit olfactory processing is preserved in this population. An olfactory visuomotor priming paradigm, which detects implicit olfactory processing in neurologically healthy participants, was utilized to investigate motor control in relation to olfactory signals in a group of IPD patients. Two control groups were also considered: 12 vascular Parkinson's disease (VPD) in whom normal olfactory abilities are typically reported and 12 neurologically healthy participants. All of the participants were asked to perform reach-to-grasp movements toward large or small targets following olfactory cues delivered by a computer-controlled olfactometer. The odor was either 'size' congruent with the target (e.g., strawberry or apple, respectively) or incongruent (e.g., apple or strawberry, respectively). A bend sensor glove (CyberGlove) was used to measure the hand kinematics. Facilitation effects were noted in all the groups with regard to movement time. If a congruent rather than an incongruent odor was delivered, the movement time of the reach-to-grasp was shortened and facilitation effects in maximum grip amplitude were noted in both the IPD and the VPD groups. The maximum grip amplitude was smaller when no odor, as compared to a congruent odor, was delivered. The present results suggest that implicit olfactory processing affects motor control in IPD patients favoring less severe bradykinesia and hand movement hypometria. Once confirmed, these findings could be useful when rehabilitation strategies are being hypothesized for these patients.