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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.


Related in: MedlinePlus

Saccadic responses in patients and elderly controls. (A) Average saccadic peak velocity in degrees per second as a function of reward for elderly controls (dashed grey), Parkinson’s disease ON (blue) and Parkinson’s disease OFF (red). Significantly steeper saccade reward sensitivity slopes were present in Parkinson’s disease ON compared to Parkinson’s disease OFF and elderly controls. There was increased invigoration of movements for bigger rewards in all groups, with increased incline when ON dopamine. (B) Visual representation of sensitivity slopes when changes in amplitude were accounted for by linear regression. Residual velocities plotted as a function of reward show that greater reward sensitivity is still present in Parkinson’s disease ON when compared to Parkinson’s disease OFF and compared to elderly participants at the largest level of reward. PD = Parkinson’s disease.
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aww188-F6: Saccadic responses in patients and elderly controls. (A) Average saccadic peak velocity in degrees per second as a function of reward for elderly controls (dashed grey), Parkinson’s disease ON (blue) and Parkinson’s disease OFF (red). Significantly steeper saccade reward sensitivity slopes were present in Parkinson’s disease ON compared to Parkinson’s disease OFF and elderly controls. There was increased invigoration of movements for bigger rewards in all groups, with increased incline when ON dopamine. (B) Visual representation of sensitivity slopes when changes in amplitude were accounted for by linear regression. Residual velocities plotted as a function of reward show that greater reward sensitivity is still present in Parkinson’s disease ON when compared to Parkinson’s disease OFF and compared to elderly participants at the largest level of reward. PD = Parkinson’s disease.

Mentions: A repeated measures ANOVA performed on saccadic peak velocity for the three reward levels in young controls demonstrates a main effect of reward [F(1.4,26.6) = 18.24, P < 0.001]. There was a significant increase between each reward level (all comparisons between rewards were significant, P < 0.01). This effect was also present in elderly controls [main effect of reward, F(1.7,52.0) = 9.2, P < 0.001]. Again, peak velocity significantly increased with each increment in reward (all comparisons P < 0.05; Fig. 6A). It is well established that peak velocity scales with saccade amplitude—the so-called ‘main sequence’ (Bahill et al., 1975). It is possible that the increases in peak velocity we observed with reward reflect only increases in saccade amplitude: that eye movements become larger when more reward is on offer. To examine this issue, the amplitude of each saccade was factored out by performing a linear regression on the raw saccade data and obtaining residual velocities (Fig. 6B). Sensitivity to reward remained even after factoring out amplitude changes for both controls and Parkinson’s disease patients, so the effect of incentives on peak velocity cannot be attributed to an invigoration of saccade length.Figure 6


Reward sensitivity deficits modulated by dopamine are associated with apathy in Parkinson ’ s disease
Saccadic responses in patients and elderly controls. (A) Average saccadic peak velocity in degrees per second as a function of reward for elderly controls (dashed grey), Parkinson’s disease ON (blue) and Parkinson’s disease OFF (red). Significantly steeper saccade reward sensitivity slopes were present in Parkinson’s disease ON compared to Parkinson’s disease OFF and elderly controls. There was increased invigoration of movements for bigger rewards in all groups, with increased incline when ON dopamine. (B) Visual representation of sensitivity slopes when changes in amplitude were accounted for by linear regression. Residual velocities plotted as a function of reward show that greater reward sensitivity is still present in Parkinson’s disease ON when compared to Parkinson’s disease OFF and compared to elderly participants at the largest level of reward. PD = Parkinson’s disease.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5035817&req=5

aww188-F6: Saccadic responses in patients and elderly controls. (A) Average saccadic peak velocity in degrees per second as a function of reward for elderly controls (dashed grey), Parkinson’s disease ON (blue) and Parkinson’s disease OFF (red). Significantly steeper saccade reward sensitivity slopes were present in Parkinson’s disease ON compared to Parkinson’s disease OFF and elderly controls. There was increased invigoration of movements for bigger rewards in all groups, with increased incline when ON dopamine. (B) Visual representation of sensitivity slopes when changes in amplitude were accounted for by linear regression. Residual velocities plotted as a function of reward show that greater reward sensitivity is still present in Parkinson’s disease ON when compared to Parkinson’s disease OFF and compared to elderly participants at the largest level of reward. PD = Parkinson’s disease.
Mentions: A repeated measures ANOVA performed on saccadic peak velocity for the three reward levels in young controls demonstrates a main effect of reward [F(1.4,26.6) = 18.24, P < 0.001]. There was a significant increase between each reward level (all comparisons between rewards were significant, P < 0.01). This effect was also present in elderly controls [main effect of reward, F(1.7,52.0) = 9.2, P < 0.001]. Again, peak velocity significantly increased with each increment in reward (all comparisons P < 0.05; Fig. 6A). It is well established that peak velocity scales with saccade amplitude—the so-called ‘main sequence’ (Bahill et al., 1975). It is possible that the increases in peak velocity we observed with reward reflect only increases in saccade amplitude: that eye movements become larger when more reward is on offer. To examine this issue, the amplitude of each saccade was factored out by performing a linear regression on the raw saccade data and obtaining residual velocities (Fig. 6B). Sensitivity to reward remained even after factoring out amplitude changes for both controls and Parkinson’s disease patients, so the effect of incentives on peak velocity cannot be attributed to an invigoration of saccade length.Figure 6

View Article: PubMed Central - PubMed

ABSTRACT

Apathy is extremely common in neurodegenerative disorders such as Parkinson&rsquo;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.


Related in: MedlinePlus