Disconnecting force from money: Effects of basal ganglia damage on incentive motivation

Laboratoire INSERM U610, Institut Fédératif de Recherches en Neurosciences, Université Pierre et Marie Curie (Paris 6), Site Pitié-Salpêtrière, F-75013 Paris, France.
Brain (Impact Factor: 9.2). 06/2008; 131(Pt 5):1303-10. DOI: 10.1093/brain/awn045
Source: PubMed


Bilateral basal ganglia lesions have been reported to induce a particular form of apathy, termed auto-activation deficit (AAD), principally defined as a loss of self-driven behaviour that is reversible with external stimulation. We hypothesized that AAD reflects a dysfunction of incentive motivation, a process that translates an expected reward (or goal) into behavioural activation. To investigate this hypothesis, we designed a behavioural paradigm contrasting an instructed (externally driven) task, in which subjects have to produce different levels of force by squeezing a hand grip, to an incentive (self-driven) task, in which subjects can win, depending on their hand grip force, different amounts of money. Skin conductance was simultaneously measured to index affective evaluation of monetary incentives. Thirteen AAD patients with bilateral striato-pallidal lesions were compared to thirteen unmedicated patients with Parkinson's; disease (PD), which is characterized by striatal dopamine depletion and regularly associated with apathy. AAD patients did not differ from PD patients in terms of grip force response to external instructions or skin conductance response to monetary incentives. However, unlike PD patients, they failed to distinguish between monetary incentives in their grip force. We conclude that bilateral striato-pallidal damage specifically disconnects motor output from affective evaluation of potential rewards.

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    • "As stated above, bilateral basal ganglia lesions have been reported to induce a particular form of apathy, termed auto-activation deficit, principally defined as a loss of self-driven behavior that is reversible with external stimulation. Schmidt et al. (2008) proposed that bilateral striato-pallidal damage, observed in PD, specifically disconnects motor output from affective evaluation of potential rewards. "
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    • "It may be that clinical groups exhibit a distinctly different pattern of motivational deficits (cf. Schmidt et al., 2008) to the ones we observed in the healthy population. However, our observations appear to echo some of the previously described characteristics of auto-activation deficit: behavioral inertia that is reversed by strong enough external incentives, or solicitors (Levy and Dubois, 2006). "
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    • "Our finding that even “off” medication patients improved their ITs with the prospect of monetary incentive (Fig. 2a,b) may perhaps be surprising, but is consistent with previous studies, which demonstrated a preserved ability of PD patients to translate the expectation of reward into generation of faster movements or greater physical force, even when unmedicated. For example, non-apathetic bradykinetic PD patients “off” medication, in the presence of monetary incentive, were able to increase hand grip force [17] or to complete a spatial search task faster [18]. Nevertheless, our results are different from those of Shiner et al. [19], who reported that PD patients “off” dopaminergic treatment failed to modulate movement speed in the face of monetary reward. "
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