A deficiency in which neurotransmitter is linked to Parkinson's disease?

Parkinson's disease is primarily associated with a deficiency in dopamine, a neurotransmitter that plays a critical role in coordinating movement and motor control. In the brains of individuals with Parkinson's disease, the neurons that produce dopamine become damaged and gradually die. This loss of dopamine leads to the hallmark symptoms of Parkinson's, including tremors, rigidity, and slowed movements. The insufficient levels of dopamine disrupt the normal function of the basal ganglia, a group of brain structures involved in movement regulation.

In contrast, other neurotransmitters listed in the question have roles that do not directly relate to the motor control issues seen in Parkinson's disease. For instance, serotonin is more commonly associated with mood regulation and is linked to conditions like depression and anxiety. Norepinephrine is involved in attention and response actions, while acetylcholine has important roles in memory and learning as well as in muscle activation. Thus, while all these neurotransmitters are important for various functions within the nervous system, dopamine's specific link to motor function makes it the neurotransmitter most clearly associated with Parkinson's disease.