Which of the following is NOT a symptom of upper motor neuron lesions?

Hypotonicity is not a symptom typically associated with upper motor neuron lesions. Instead, upper motor neuron lesions are characterized by increased muscle tone or spasticity, which is the state of resistance to passive movement due to the heightened reflex activity.

In patients with upper motor neuron lesions, you would commonly observe muscle weakness, as the upper motor neurons are responsible for conveying messages from the brain to initiate voluntary movements. Pathologic reflexes, such as the Babinski reflex, can also emerge due to the disruption of normal reflex pathways in the central nervous system.

In contrast, hypotonicity is more indicative of lower motor neuron lesions. These lesions impact the final common pathway, leading to a decrease in muscle tone and reflexes. Therefore, recognizing hypotonicity as not characteristic of upper motor neuron lesions is essential in understanding the differentiation between upper and lower motor neuron pathologies.