Final answer:
The input nuclei of the basal ganglia are primarily associated with motor planning and initiation.
Step-by-step explanation:
The function primarily associated with the input nuclei of the basal ganglia is motor planning and initiation. The basal ganglia, including the input nuclei, are involved in assessing cortical movement commands and comparing them with the general state of the individual. They play a crucial role in motor functions. For example, symptoms of Parkinson's and Huntington's diseases are largely related to dysfunction within the basal ganglia.