Roll tilt reflexes after vestibulospinal tract lesions

Area of Science:

• Neuroscience
• Vestibular System
• Motor Control

Background:

• Vestibulospinal tracts are critical for maintaining posture and balance.
• Understanding their specific roles in forelimb and neck reflexes is essential for comprehending motor control.

Purpose of the Study:

• To investigate the functional roles of the medial and lateral vestibulospinal tracts.
• To determine their influence on vestibular reflexes in forelimb and neck extensor muscles during roll tilt.

Main Methods:

• Decerebrate cat preparation.
• Lesions of the medial longitudinal fasciculus (containing the medial vestibulospinal tract).
• Spinal lesions at C2-C3 (hemisections and lateral vestibulospinal tract lesions).
• Electromyography (EMG) recording from forelimb and neck extensor muscles.
• Administration of L-Dopa to modulate background excitability.

Main Results:

• Medial vestibulospinal tract lesions had minor effects on reflex phase and gain.
• Lateral vestibulospinal tract lesions abolished ipsilateral triceps EMG and caused partial loss in the contralateral limb.
• Contralateral forelimb tilt reflex showed a 180-degree phase reversal, indicating crossed otolith-spinal input.
• Neck extensor responses were largely unaffected by spinal lesions.

Conclusions:

• The lateral vestibulospinal tract plays a significant role in modulating forelimb muscle activity and receiving crossed otolith-spinal input.
• The medial vestibulospinal tract has a less prominent role in these specific vestibular reflexes.
• Vestibular reflexes in neck extensors are relatively independent of these specific vestibulospinal pathways.