Substantia Nigra Pars Compacta (SNc)

The substantia nigra pars compacta (SNc) is a region in the brain that plays a crucial role in the regulation of movements and in reward-related learning^[1].

The substantia nigra is located in the mesencephalon, a small region located towards the base of the brain. The term "substantia nigra" means "black substance" in Latin, which is named for its dark colour due to high levels of neuromelanin in dopaminergic neurons^[2]. The substantia nigra itself is divided into two parts: the pars compacta (SNc) and the pars reticulata (SNr).

The SNc is particularly known for its role in producing dopamine, a vital neurotransmitter for numerous functions in the brain. The neurons in the SNc, also known as dopaminergic neurons, have extensive axonal projections that reach out to various parts of the brain^[1].

Functionally, the SNc is involved in the regulation of motor control and is integral to the reward system^[3]. The dopaminergic neurons project from the SNc to the striatum, which is part of the basal ganglia. This pathway, known as the nigrostriatal pathway, is critical in modulating motor function. In conditions like Parkinson's disease, the loss of dopaminergic neurons in the SNc leads to the characteristic motor symptoms of the disease, such as tremors, rigidity, bradykinesia (slowness of movement), and postural instability^[4].

Furthermore, the dopaminergic neurons in the SNc also project to other areas of the brain, including the nucleus accumbens, which is a part of the ventral striatum, and the prefrontal cortex^[5]. This is known as the mesocortical pathway, which is deeply involved in reward-based learning and motivation, the processing of aversive stimuli, and in the modulation of various aspects of cognition and emotion.