Unilateral forelimb deafferentation in the monkey: purposive movement

Area of Science:

• Neuroscience
• Primate behavior
• Motor control

Background:

• Unilateral dorsal rhizotomy (UDR) is a surgical procedure that severs sensory nerve roots.
• The use of deafferented limbs in primates after UDR is not fully understood.
• Previous theories suggested cross-spinal inhibition or learned disuse might explain limited limb function.

Purpose of the Study:

• To investigate the functional use of deafferented limbs in monkeys after UDR.
• To test hypotheses regarding cross-spinal inhibition and learned disuse.
• To understand the role of sensory feedback in motor control.

Main Methods:

• Monkeys underwent unilateral dorsal rhizotomy (C2-T3).
• Deafferented limbs were used to retrieve unseen food pellets.
• The intact limb's movement was restricted by a container.
• Limb use was observed after the intact limb was released.

Main Results:

• Monkeys successfully used their deafferented limbs to retrieve food when the intact limb was immobilized.
• Deafferented limb use ceased when the intact limb was no longer confined.
• Protracted use of the deafferented limb did not lead to sustained use when the intact limb was free.

Conclusions:

• Findings challenge explanations of deafferented limb non-use based on cross-spinal inhibition.
• The results also cast doubt on the learned disuse hypothesis.
• Sensory feedback and the availability of an intact limb significantly influence deafferented limb utilization.