Importance of the visual cortex for postural stabilization: inferences from pigeon and frog data

Area of Science:

• Neuroscience
• Vestibular System
• Visual Perception

Background:

• Optokinetic stimulation influences postural balance through visual-vestibular convergence.
• The specific visual pathways (subcortical vs. cortical) involved in conveying optokinetic information to the central vestibular system remain unclear.

Purpose of the Study:

• To investigate the functional significance of the visual cortex in processing optokinetic information for postural control.
• To determine if the presence of a visual cortex is necessary for the perception of rollvection and compensatory postural adjustments.

Main Methods:

• Behavioral experiments were conducted on frogs (lacking a visual cortex) and pigeons (possessing a primitive visual cortex).
• Optokinetic stimulation in roll was used to induce self-motion perception (rollvection) and apparent body tilt.
• Lateral postural sway was measured to quantify compensatory postural adjustments.

Main Results:

• Pigeons exhibited tonic 'compensatory' postural adjustments towards the direction of pattern motion, similar to humans.
• Frogs did not show these compensatory postural adjustments, indicating a lack of rollvection perception.
• These findings align with the absence of visual-vestibular convergence in frog vestibular nuclei and brainstem nystagmus velocity storage.

Conclusions:

• The visual cortex is essential for the perception of rollvection and for eliciting compensatory postural adjustments during optokinetic stimulation.
• The evolutionary development of the visual cortex is linked to sophisticated visual-vestibular integration for balance control.
• Results in animals correlate with human data from hemianopic patients, further supporting the role of the visual cortex.