Altered reward-related neural responses in non-manifesting carriers of the Parkinson disease related LRRK2 mutation

Disturbances in reward processing occur in Parkinson's disease (PD) however it is unclear whether these are solely drug-related. We applied an event-related fMRI gambling task to a group of non-manifesting carriers (NMC) of the G2019S mutation in the LRRK2 gene, in order to assess the reward network in an at risk population for future development of PD. Sixty-eight non-manifesting participants, 32 of which were non-manifesting non-carriers (NMNC), performed a gambling task which included defined intervals of anticipation and response to both reward and punishment in an fMRI setup. Behavior and cerebral activations were measured using both hypothesis driven and whole brain analysis. NMC demonstrated higher trait anxiety scores (p=0.04) compared to NMNC. Lower activations were detected among NMC during risky anticipation in the left nucleus accumbens (NAcc) (p=0.05) and during response to punishment in the right insula (p=0.02), with higher activations among NMC during safe anticipation in the right insula (p=0.02). Psycho-Physiological Interaction (PPI) analysis from the NAcc and insula revealed differential connectivity patterns. Whole brain analysis demonstrated divergent between-group activations in distributed cortical regions, bilateral caudate, left midbrain, when participants were required to press the response button upon making their next chosen move. Abnormal neural activity in both the reward and motor networks were detected in NMC indicating involvement of the ventral striatum regardless of medication use in at risk individuals for future development of PD.