What is a hallmark of peripheral facial paralysis during the eyebrow raising test?

In the context of peripheral facial paralysis, which is often associated with conditions like Bell's palsy, the hallmark finding during the eyebrow raising test is that the forehead does not wrinkle. This is due to the partial or complete loss of function in the facial nerve on the affected side, which leads to the inability to engage the muscles that control eyebrow movement and forehead wrinkling.

When performing the eyebrow raising test, if the forehead does not wrinkle, it indicates that the muscles responsible for this action—innervated by the facial nerve—are compromised. This is pivotal in differentiating between central and peripheral facial paralysis. In central facial paralysis, the upper facial muscles (including those of the forehead) can often still be activated because they receive bilateral innervation from the brain; hence, complete wrinkling might still occur on one side. In contrast, with peripheral facial paralysis, the affected side's muscles will remain at rest and show no wrinkling, confirming the diagnosis.

The other options do not accurately reflect this hallmark. For instance, pronounced wrinkles in the forehead would suggest normal nerve function, while both eyebrows being easily raised would indicate no paralysis. Thus, the correct interpretation of the eyebrow raising test points to the absence of forehead wrinkles on the affected