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1 Department of Neuroscience, Nobel institute for Neurophysiology, Karolinska Institutet, Stockholm, Sweden
2 Department of Neuroscience, Nobel institute for Neurophysiology, Karolinska Institutet, Sweden
* To whom correspondence should be addressed. E-mail: sten.grillner{at}ki.se.
The intrinsic function of the brainstem-spinal cord networks eliciting the locomotor synergy is well described in the lamprey -- a vertebrate model system. This study addresses the role of tectum in integrating eye, body orientation and locomotor movements as in steering and goal directed behavior. Electrical stimuli were applied to different areas within the optic tectum in head-restrained semi-intact lampreys (n=40). The motion of the eyes and body were recorded simultaneously (video-taped). Brief pulse trains (< 0.5 s) elicited only eye movements, but with longer stimuli (> 0.5 s) lateral bending movements of the body (orientation movements) were added, and with even longer stimuli locomotor movements were initiated. Depending on the tectal area stimulated, four characteristic response patterns were observed. In a lateral area conjugate horizontal eye movements combined with lateral bending movements of the body and locomotor movements were elicited, depending on stimulus duration. The amplitude of the eye movement and bending movements was site specific within this region. In a rostro-medial area, bilateral downward vertical eye movements occurred. In a caudo-medial tectal area, large amplitude undulatory body movements akin to struggling behaviour were elicited, combined with large amplitude eye movements that were antiphasic to the body movements. The alternating eye movements were not dependent on vestibulo-ocular reflexes. Finally, in a caudo-lateral area locomotor movements without eye or bending movements could be elicited. These results show that tectum can provide integrated motor responses of eye, body orientation and locomotion of the type that would be required in goal-directed locomotion.
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