Cerebellectomy, the surgical removal of the cerebellum or part of it, in monkeys has been extensively studied to understand the cerebellum’s critical role in motor control and coordination. After postoperative recovery, when a monkey is tasked with pressing a bar, several characteristic motor dysfunctions can be observed, which shed light on the cerebellum’s functions.

Motor Deficits After Cerebellectomy

Research consistently shows that cerebellectomy results in impairments related to fine motor control rather than paralysis. Monkeys retain the ability to move their limbs but often exhibit:

• Overshoot of target during reaching: The monkey’s hand overshoots the intended target when reaching for an object, reflecting a lack of movement precision and poor trajectory control. This symptom is known as dysmetria.

• Intention tremor: As the monkey tries to perform a precise action like pressing a bar, it displays tremors that worsen with the attempt to initiate the movement, a hallmark of cerebellar dysfunction.

• Preservation of limb movement ability: Contrary to paralysis, the monkey can move its forelimbs, ruling out the inability to move as a typical consequence.

• No instinctual substitution: The monkey does not resort to pressing the bar with the mouth, indicating that basic motor planning is intact but motor execution is impaired.

Scientific Evidence from Studies

Studies involving cerebellectomy or cerebellar blockade in monkeys show increased variability in movement trajectories and impaired adaptation to motor tasks. The cerebellum’s role in refining motor commands makes the motor outputs less accurate and coordinated post-surgery. Electrical recordings confirm disrupted cerebellar-cortical interactions, which normally ensure smooth, well-timed movements. Importantly, despite motor impairments, the motor cortex and other brain regions maintain the ability to initiate movement, explaining why the limbs remain movable.pubmed.ncbi.nlm.nih+1

Correct Observations Post-Cerebellectomy

Based on these established scientific findings, the correct observations following cerebellectomy in a monkey attempting to press a bar are:

• Its hand would overshoot the target while reaching the bar (Option A).

• It would show intention tremor while trying to press the bar (Option C).

The monkey retains limb movement (ruling out B), and there is no typical compensatory use of the mouth instead of the hand (ruling out D).

Conclusion

The correct answer for the question is:
(1) A and C