Abstract
The dopaminergic neurotransmitter system is critically involved in promoting plasticity in auditory cortex. We combined functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to investigate dopaminergic modulation of neural activity in auditory cortex during instrumental learning. Volunteers either received 100 mg L-dopa (Madopar) or placebo in an appetitive, differential instrumental conditioning paradigm, which involved learning that a specific category of frequency modulated tones predicts a monetary reward when fast responses were made in a subsequent reaction time task. The other category of frequency modulated tones was not related to a reward. Our behavioral data provides evidence that dopaminergic stimulation differentially impacts on the speed of instrumental responding in rewarded and unrewarded trials. L-dopa increased neural BOLD activity in left auditory cortex to tones in rewarded and unrewarded trials. This increase was related to plasma L-dopa levels and learning rate. Our data thus provides evidence for dopaminergic modulation of neural activity in auditory cortex, which occurs for both auditory stimuli related to a later reward and those not related to a reward.
Highlights
The cortical representation of sensory stimuli is modulated by experience [1,2,3,4,5]
We aimed to investigate whether dopaminergic stimulation modulates representations of relevant stimuli in human auditory cortex
Our results show that neural activity in the auditory cortex during auditory instrumental learning was similar for reward predicting (CS+) and unrewarded (CS2) tones but generally increased after dopaminergic stimulation
Summary
The cortical representation of sensory stimuli is modulated by experience [1,2,3,4,5]. [17]) point to a crucial role of dopaminergic neurons within the ventral tegmental area (VTA) for the development of learning related plasticity. This assumption is further supported by several studies reporting significant effects of VTA activity on learning and long-term potentiation [18,19]. In line with these studies, it has been shown that the dopaminergic neurotransmitter system is involved in enhancing plasticity in auditory cortex [13,20,21,22]. Increased dopaminergic activity at the time point of initial learning promotes later memory formation via gene activation and synaptic remodeling [24]
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