Final answer:
The reticular formation is the group of nuclei within the brainstem responsible for sleep-wake cycles and maintaining alertness.
Step-by-step explanation:
The group of loosely packed nuclei within the entire length of the brainstem that is involved in cyclic activities such as sleep-wake cycles is known as the reticular formation. It is a diffuse region of gray matter that plays a crucial role in regulating sleep, wakefulness, and states of consciousness. This formation is responsible for processing cranial nerve information and helps maintain the body in a state of alertness.
In contrast, the basal ganglia (also known as basal nuclei) are involved in motor control and are affected in disorders such as Parkinson's and Huntington's diseases. The hippocampus is associated with learning and memory, while the amygdala is linked to emotional responses.