A basal ganglia lesion is most likely to cause which syndrome?

• A. Parkinsonism features such as bradykinesia and rigidity.
• B. Pure sensory loss.
• C. Seizures.
• D. Visual field defect.

Answer: (A)

Movement is regulated by basal ganglia circuits that modulate thalamocortical activity through direct and indirect pathways. When a basal ganglia lesion disrupts these circuits, the balance shifts toward increased inhibitory output from the internal globus pallidus and substantia nigra pars reticulata, leading to reduced thalamic stimulation of the motor cortex. This produces the slowness and stiffness characteristic of parkinsonism, notably bradykinesia and rigidity.

Other presentations like pure sensory loss point to damage in sensory pathways such as the thalamus or sensory cortex; seizures arise from cortical hyperexcitability; and visual field defects involve the occipital cortex or optic radiations. Basal ganglia lesions, by contrast, predominantly disrupt movement control rather than primary sensation or vision.