Dopaminergic mesocortical projections to M1: role in motor learning and motor cortex plasticity

Although the architecture of a dopaminergic (DA) system within the primary motorcortex (M1) was well characterized anatomically, its functional significance remainedobscure for a long time. Recent studies in rats revealed that the integrity ofdopaminergic fibers in M1 is a prerequisite for successful acquisition of motor skills.This essential contribution of DA for motor learning is plausible as it modulates M1circuitry at multiple levels thereby promoting plastic changes that are required forinformation storage: at the network level, DA increases cortical excitability andenhances the stability of motor maps. At the cellular level, DA induces the expressionof learning related genes via the transcription factor c-fos. At the level of synapses,DA is required for the formation of long-term potentiation (LTP), a mechanism thatlikely is a fingerprint of a motor memory trace within M1. Dopaminergic fibersinnervating M1 originate within the midbrain, precisely the ventral tegmental area(VTA) and the medial portion of substantia nigra (SN). Thus, they could be part of themeso-cortico-limibic pathway – a network that provides information about saliencyand motivational value of an external stimulus and is commonly referred as