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Reward sensitivity deficits modulated by dopamine are associated with apathy in Parkinson ’ s disease

View Article: PubMed Central - PubMed

ABSTRACT

Apathy is extremely common in neurodegenerative disorders such as Parkinson’s disease. Muhammed et al. report that lack of sensitivity to rewards may underlie apathy, with dopamine playing a modulatory role. The study provides a basis for objective clinical markers of motivation and treatment efficacy in neurodegenerative conditions.

No MeSH data available.


Experimental paradigm. (A) Participants heard a recorded auditory cue that informed them of the maximum reward available for each trial: ‘0p/10p/50p maximum’. After a randomly variable fore-period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared. Participants were rewarded according to reaction time, with the reward obtained displayed within the target disc in pence (e.g. 37p). (B) The absolute amount of reward earned varied with reaction time, but crucially was dynamically adjusted according to mean reaction time of each participant at any point during the experiment. To calculate the reward obtained for each trial, an adaptive exponential fall-off based on the mean reaction time of the preceding 20 trials was used. Participants received a proportion of the maximum amount on offer dependent on performance. This adaptive procedure allowed difficulty level to be maintained consistently over the experiment and importantly provided equal overall reward amounts to all participants. Thus it was not the case that apathetic patients earned less as they proceeded through the task nor did they have less external incentivization.
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aww188-F1: Experimental paradigm. (A) Participants heard a recorded auditory cue that informed them of the maximum reward available for each trial: ‘0p/10p/50p maximum’. After a randomly variable fore-period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared. Participants were rewarded according to reaction time, with the reward obtained displayed within the target disc in pence (e.g. 37p). (B) The absolute amount of reward earned varied with reaction time, but crucially was dynamically adjusted according to mean reaction time of each participant at any point during the experiment. To calculate the reward obtained for each trial, an adaptive exponential fall-off based on the mean reaction time of the preceding 20 trials was used. Participants received a proportion of the maximum amount on offer dependent on performance. This adaptive procedure allowed difficulty level to be maintained consistently over the experiment and importantly provided equal overall reward amounts to all participants. Thus it was not the case that apathetic patients earned less as they proceeded through the task nor did they have less external incentivization.

Mentions: An infrared eye tracker (Eyelink 1000, SR Research) was used to monitor pupil diameter and eye position. Participants were instructed that the task involved making quick eye movements, the faster they looked at a target, the greater the proportion of reward on offer they would obtain (Fig. 1A). Each trial commenced with the onset of a disc at screen centre. After they had fixated this for 500 ms, participants heard a recorded voice that informed them of the maximum reward available for that particular trial: ‘0p/10p/50p maximum’. Subsequently, after a randomly variable period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared randomly either to the left or right. The targets measured 4° in diameter and appeared at 11° eccentricity.Figure 1


Reward sensitivity deficits modulated by dopamine are associated with apathy in Parkinson ’ s disease
Experimental paradigm. (A) Participants heard a recorded auditory cue that informed them of the maximum reward available for each trial: ‘0p/10p/50p maximum’. After a randomly variable fore-period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared. Participants were rewarded according to reaction time, with the reward obtained displayed within the target disc in pence (e.g. 37p). (B) The absolute amount of reward earned varied with reaction time, but crucially was dynamically adjusted according to mean reaction time of each participant at any point during the experiment. To calculate the reward obtained for each trial, an adaptive exponential fall-off based on the mean reaction time of the preceding 20 trials was used. Participants received a proportion of the maximum amount on offer dependent on performance. This adaptive procedure allowed difficulty level to be maintained consistently over the experiment and importantly provided equal overall reward amounts to all participants. Thus it was not the case that apathetic patients earned less as they proceeded through the task nor did they have less external incentivization.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035817&req=5

aww188-F1: Experimental paradigm. (A) Participants heard a recorded auditory cue that informed them of the maximum reward available for each trial: ‘0p/10p/50p maximum’. After a randomly variable fore-period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared. Participants were rewarded according to reaction time, with the reward obtained displayed within the target disc in pence (e.g. 37p). (B) The absolute amount of reward earned varied with reaction time, but crucially was dynamically adjusted according to mean reaction time of each participant at any point during the experiment. To calculate the reward obtained for each trial, an adaptive exponential fall-off based on the mean reaction time of the preceding 20 trials was used. Participants received a proportion of the maximum amount on offer dependent on performance. This adaptive procedure allowed difficulty level to be maintained consistently over the experiment and importantly provided equal overall reward amounts to all participants. Thus it was not the case that apathetic patients earned less as they proceeded through the task nor did they have less external incentivization.
Mentions: An infrared eye tracker (Eyelink 1000, SR Research) was used to monitor pupil diameter and eye position. Participants were instructed that the task involved making quick eye movements, the faster they looked at a target, the greater the proportion of reward on offer they would obtain (Fig. 1A). Each trial commenced with the onset of a disc at screen centre. After they had fixated this for 500 ms, participants heard a recorded voice that informed them of the maximum reward available for that particular trial: ‘0p/10p/50p maximum’. Subsequently, after a randomly variable period of 1400, 1500 or 1600 ms the central fixation disc disappeared and concurrently a new target disc appeared randomly either to the left or right. The targets measured 4° in diameter and appeared at 11° eccentricity.Figure 1

View Article: PubMed Central - PubMed

ABSTRACT

Apathy is extremely common in neurodegenerative disorders such as Parkinson’s disease. Muhammed et al. report that lack of sensitivity to rewards may underlie apathy, with dopamine playing a modulatory role. The study provides a basis for objective clinical markers of motivation and treatment efficacy in neurodegenerative conditions.

No MeSH data available.