Which part of the brain is affected in truncal ataxia?

Truncal ataxia is primarily associated with dysfunction in the vermis of the cerebellum. The vermis is the central part of the cerebellum and plays a crucial role in controlling balance and posture. When this area is affected, it results in a characteristic instability while sitting or standing and difficulty with balance, leading to the clinical manifestation known as truncal ataxia.

The cerebellum as a whole is involved in coordinating voluntary movements, and damage to it can lead to various types of ataxia, but truncal ataxia specifically points to involvement of the vermis. This distinction is important, as other parts of the cerebellum may cause different types of ataxias that do not primarily affect the trunk and posture in the same manner.

In contrast, while the brainstem is involved in motor control and can affect the function of the cerebellum, it does not specifically correlate with truncal ataxia. The cerebral cortex also has various roles in motor control but is not directly responsible for the ataxia seen in vermis dysfunction. Hence, the most accurate answer in the context of truncal ataxia is the vermis of the cerebellum.