Solution
= Solution
\b[Human disorders show that <motivation> depends on several distinguishable operations: initiating activity, translating incentive value into effort, evaluating outcomes and sustaining goal-directed behavior.] A person may be able to execute an instructed movement yet fail to initiate useful action, or may respond differently to <reward> and effort without a global loss of <intelligence>. These dissociations argue against equating <motivation> with motor strength or with a single quantity of pleasure.
A striking starting point is <auto-activation deficit>. <Dominique Laplane> and colleagues described three people with marked reduction in spontaneous mental and behavioral activity after toxic encephalopathy and bilateral <basal ganglia> <brain lesions>, especially involving the <globus pallidus> on the available scans. Intellectual capacities were relatively preserved and motor impairment could be mild. External stimulation could reverse the apparent inactivity. This contrast suggested a problem in self-activation rather than inability to perform every relevant cognitive or motor operation.<Pure psychic akinesia with bilateral lesions of basal ganglia by Dominique Laplane and others>[1984, spontaneous versus externally elicited activity and CT findings]{ref}
The cases were mechanistically informative but not anatomically pure experiments. Toxic injury can affect more than the structures visible on a scan, and reduced initiation can interact with executive, emotional and motor processes. The observation therefore implicates <basal ganglia>–frontal systems in internally generated activity without showing that one nucleus contains all <motivation>. It also motivates assessing spontaneous behavior separately from performance after repeated prompting.
<Liane Schmidt> and colleagues tested a more specific incentive-to-action hypothesis. They contrasted an instructed handgrip task, requiring specified force levels, with an incentive task where effort could earn money. Patients with <basal ganglia> damage and auto-activation difficulty could use external instructions to produce force but showed abnormal translation of incentives into effort. The apparatus makes the dissociation concrete: an available motor response does not ensure that anticipated <reward> will appropriately energize it.<Disconnecting force from money by Liane Schmidt and others>[2008, instructed versus incentive-driven handgrip tasks]{ref}
This helps separate motor capacity from motivational use of that capacity. Nevertheless, monetary incentives also require understanding task contingencies, representing value and maintaining the goal. A reduced force response does not uniquely identify absence of pleasure. The strength of the design is the contrasting instruction condition; the remaining question is which valuation, activation or control operation prevents self-driven use of the preserved response.
<Parkinson's disease> offers converging evidence while introducing its own confounds. <Campbell Le Heron> and colleagues tested 39 patients, with and without clinical <apathy>, ON and OFF their usual dopaminergic medication, alongside 32 controls. Choices varied both monetary <reward> and required physical effort. <Apathy> and medication state were associated with different patterns across the <reward>–effort space, rather than one uniform decrease in willingness to act. This supports distinguishing clinical motivational difficulty from the complete set of effects produced by changing <dopamine> availability.<Distinct effects of apathy and dopamine on effort-based decision-making in Parkinson's disease by Campbell Le Heron and others>[2018, reward/effort choice, apathy groups and ON/OFF comparison]{ref}
The design is stronger than comparing raw movement speed alone, but an ON/OFF contrast is not a selective perturbation of one psychological computation. Medication changes motor function and potentially learning, alertness and response vigor. <Apathy> groups are not randomly assigned, and comprehension, <depression>, fatigue and motor capacity can differ. Interpreting choice patterns therefore requires suitable calibration and comparison measures. <Dopamine> sensitivity does not justify the statement that <dopamine> is simply a pleasure signal.
A small <statistical model> illustrates why <effort-based decision-making> experiments must vary both benefits and costs. Suppose acceptance depends on $U=\alpha R-\kappa E$, where $R$ is <reward>, $E$ effort, $\alpha$ <reward> gain and $\kappa$ effort cost. With a fixed <logistic function> as the choice rule, a lower <reward> gain and a higher effort cost can produce exactly the same acceptance <probability> at one offer. This <single-offer reward-effort ambiguity> motivates varying both dimensions to distinguish their predictions within the model. These are alternative explanations to test, not parameter estimates obtained merely by diagnosing <apathy>.
\Image[/past-exam-of-the-cognitive-neurology-course-of-the-university-of-oxford/2022-reward-effort-ambiguity.png]
{title=One offer cannot distinguish reduced reward gain from increased effort cost}
{description=Original constructed logistic-choice illustration. The two parameter settings predict identical acceptance at the marked offer but different patterns elsewhere. The heatmaps are not patient responses, fitted clinical models or a reproduction of the Parkinson's study. Choice-noise scale is fixed for this illustration.}
Patients with <prefrontal cortex> damage reveal another component: evaluation of actions across outcomes and time. <Antoine Bechara> and colleagues introduced the procedure now called the <Iowa gambling task>, in which choices offered different short-term gains and longer-term consequences. Patients with <ventromedial prefrontal cortex> damage continued making disadvantageous choices despite relatively preserved conventional intellectual abilities. This linked real-world decision difficulty to experimentally observable valuation and learning demands.<Insensitivity to future consequences following damage to human prefrontal cortex by Antoine Bechara and others>[1994, gambling-task comparison and disadvantageous choices]{ref}
The result supports a role in using consequences to guide behavior, but the task combines <reward learning>, loss sensitivity, reversal, uncertainty and <human memory>. It does not uniquely establish one bodily-feedback mechanism or prove that the patients have no emotional responses. Similarly, <anhedonia>, reduced initiation and willingness to expend effort should be measured separately rather than treated as synonyms. Several mechanisms can produce superficially similar inactivity, and a change in one response measure does not imply a change in every form of <motivation>.
Across these disorders, the most useful inference is computational and relational. <Basal ganglia> injury distinguishes instructed action from self-activation and incentive translation; Parkinsonian comparisons distinguish aspects of <reward>–effort choice from medication-related motor and motivational effects; prefrontal damage reveals difficulty applying future consequences. These operations interact through connected systems and need not map to one region each. \b[Patient studies have transformed <motivation> from a vague explanation of behavior into separable hypotheses about initiation, valuation, effort and control, while demanding that the preserved capacities and competing explanations be tested explicitly.]