A cerebellar lesion produces motor signs that are on which side relative to the lesion?

• A. Contralateral motor deficits.
• B. Ipsilateral motor deficits.
• C. Only sensory loss.
• D. Headache without ataxia.

Answer: (B)

Cerebellar signs occur on the same side as the lesion because each cerebellar hemisphere coordinates movements of the ipsilateral limbs. When a cerebellar hemisphere is damaged, the circuitry that tunes and coordinates those same-side movements is disrupted, leading to ataxia, dysmetria, and intention tremor on that side. This pattern contrasts with lesions of the motor cortex or corticospinal tract, which produce contralateral weakness rather than pure ataxia. Sensory loss is not a hallmark of cerebellar problems, and headaches without ataxia don’t reflect cerebellar dysfunction. Therefore, motor deficits appear on the same side as the lesion.