BACKGROUND: Apathy is a common syndrome observed in many @entity16 , including in up to 70% of @entity1 with @entity191 . Mechanisms underlying apathy are poorly understood and clinically we lack robust, objective detection methods. We aimed to address this using novel objective measures of motivation and reward sensitivity in relation to apathy in @entity1 with @entity191 . METHODS: Saccadic velocity and pupil modulation by reward were used as objective metrics of motivation in @entity1 with @entity191 . In addition, differences in reward sensitivity in @entity1 off medication were compared with those on medication, and assessed in relation to apathy. 20 @entity1 with @entity191 and 21 healthy @entity1 were recruited. @entity1 were tested in counterbalanced sessions, on and off dopaminergic medication. @entity1 were asked to make saccadic eye movements for different monetary rewards, with eye position, velocity, and pupil diameter monitored with an infrared eye tracker. Faster initiation of saccades received a greater proportion of rewards. Apathy was indexed by Lille Apathy Rating Scale (LARS) scores. FINDINGS: Healthy controls and @entity1 on medication demonstrated an increase in saccadic peak velocity as reward magnitude increased (an increase by 41 deg/s [SE 20] p<0  0001, and 22  5 [4  7] p<0  0001, respectively). This reward sensitivity was lost in @entity1 off medication (5  2 [3  2], p=0  117). In all groups, pupil diameter dilated more with larger rewards (p<0  05). In @entity191 , pupil reward sensitivity was greater in @entity1 on medication than off medication, but not statistically so (p=0  06). A median split of @entity1 on medication into high motivated and low motivated groups based on LARS scores revealed a significant interaction between motivation level and rewards for saccadic peak velocity (F2,18=5  153, p=0  049), with the apathetic (low motivation) group exhibiting less reward sensitivity in saccadic peak velocity. INTERPRETATION: These findings demonstrate that saccadic velocity and pupil diameter are affected by reward magnitude and that the degree of modulation varies with motivation levels across individuals. These indices provide a novel behavioural measure for probing disorders of motivation in @entity16 such as @entity191 . Dopaminergic medication might be an effective treatment for apathy by increasing reward sensitivity, independent of effects on motor control. FUNDING: Wellcome Trust.

Mechanisms underlying apathy in XXXX .

@entity1 :: ('9606', 'Species') :: ['participants', 'Patients', 'patients', 'Participants'] @entity16 :: ('MESH:D009422', 'Disease') :: ['neurological disorders', 'neurological conditions'] @entity191 :: ('MESH:D010300', 'Disease') :: ["Parkinson's diease", "idiopathic Parkinson's disease", "Parkinson's disease"]
@entity191 :: (MESH:D010300,Disease) :: ['Parkinson's disease']
