Abstract
Psychostimulants such as d-amphetamine (AMPH) often have behavioral effects that appear paradoxical within the framework of optimal choice theory. AMPH typically increases task engagement and the effort animals exert for reward, despite decreasing reward valuation. We investigated neural correlates of this phenomenon in the anterior cingulate cortex (ACC), a brain structure implicated in signaling cost-benefit utility. AMPH decreased signaling of reward, but not effort, in the ACC of freely-moving rats. Ensembles of simultaneously recorded neurons generated task-specific trajectories of neural activity encoding past, present, and future events. Low-dose AMPH contracted these trajectories and reduced their variance, whereas high-dose AMPH expanded both. We propose that under low-dose AMPH, increased network stability balances moderately increased excitability, which promotes accelerated unfolding of a neural 'script' for task execution, despite reduced reward valuation. Noise from excessive excitability at high doses overcomes stability enhancement to drive frequent deviation from the script, impairing task execution.
Highlights
We propose that reduced reward interest is linked to decreased reward signaling by AMPH, but that animals continue to engage in the task because ensemble neural dynamics become ‘trapped’ in task-related trajectories
We examined the effect of d-amphetamine (AMPH) on behaviour and its neural correlates by means of a pre/post design in which the drug or vehicle was administered (i.p.) halfway through the session
We investigated the effect of AMPH on Anterior Cingulate Cortex (ACC) neural activity in rats performing a task with variable effort and reward
Summary
Rats typically choose to exert increased effort, such as barrier climbing or lever pressing, if the associated reward is of considerably higher value than that of lower-effort choice options.This preference is reduced or eliminated by lesions of the Anterior Cingulate Cortex (ACC)(Walton et al, 2002; Walton et al, 2003; Schweimer & Hauber, 2005; Holec et al, 2014), lesions of ventral striatum (VS) (Hauber & Sommer, 2009), or by disruption of dopamine transmission in these areas (Cousins et al, 1996; Schweimer & Hauber, 2006; Mai et al, 2012).drugs such as d-amphetamine (AMPH) that increase extracellular dopamine levels in these structures (Chiueh & Moore, 1973; Pum et al, 2007), will likely influence effort-reward choices. Rats typically choose to exert increased effort, such as barrier climbing or lever pressing, if the associated reward is of considerably higher value than that of lower-effort choice options. This preference is reduced or eliminated by lesions of the Anterior Cingulate Cortex (ACC). (Walton et al, 2002; Walton et al, 2003; Schweimer & Hauber, 2005; Holec et al, 2014), lesions of ventral striatum (VS) (Hauber & Sommer, 2009), or by disruption of dopamine transmission in these areas (Cousins et al, 1996; Schweimer & Hauber, 2006; Mai et al, 2012) Drugs such as d-amphetamine (AMPH) that increase extracellular dopamine levels in these structures (Chiueh & Moore, 1973; Pum et al, 2007), will likely influence effort-reward choices. Because utility can be expressed as the expected value discounted by its associated costs, the bias toward high-effort high-reward options under
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