Tectal Control of Locomotion, Steering, and Eye Movements in Lamprey

Abstract

Saitoh K, Ménard A, Grillner S. Tectal control of locomotion, steering, and eye movements in lamprey. J Neurophysiol 97: 3093-3108, 2007. First published February 15, 2007 doi:10.1152/jn.00639.2006. The intrinsic function of the brain stem-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 ϭ 40). Motions of the eyes and body were recorded simultaneously (videotaped). Brief pulse trains (Ͻ0.5 s) elicited only eye movements, but with longer stimuli (Ͼ0.5 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 rostromedial area, bilateral downward vertical eye movements occurred. In a caudomedial tectal area, largeamplitude undulatory body movements akin to struggling behavior were elicited, combined with large-amplitude eye movements that were antiphasic to the body movements. The alternating eye movements were not dependent on vestibuloocular reflexes. Finally, in a caudolateral 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.

Tectal microcircuit generating visual selection commands on gaze-controlling neurons

“…Although the collicular contribution to the selection process is of central importance, the underlying neuronal processes have remained elusive due to methodological limitations. It is our aim here to address this issue in a novel experimental model.The optic tectum is well developed in the lamprey, belonging to the oldest extant vertebrate group that evolved 560 million years ago (17), and it has remained conserved throughout vertebrate phylogeny (18)(19)(20)(21)(22). Afferents from retina provide a direct input to the superficial layers of the optic tectum, where a retinotopic map is formed (23-26).…”

“…Afferents from retina provide a direct input to the superficial layers of the optic tectum, where a retinotopic map is formed (23-26). The intermediate and deep layers give rise to projections to brainstem areas and a motor map is formed that is responsible for the coordination of eye, head, and body movements (22,(27)(28)(29).To uncover the mechanisms underlying visual stimulus selection for gaze reorientation, detailed intracellular analysis is needed in combination with visual activation, which has not been possible in the classic mammalian preparations. To achieve this, we have developed a preparation in lamprey that maintains the eye and the midbrain intact in vitro, which has allowed us to perform whole-cell recordings from identified gaze-controlling cells in the optic tectum, while delivering natural and focal light stimuli within the visual field and monitoring and manipulating the synaptic responses.…”

“…To achieve this, we have developed a preparation in lamprey that maintains the eye and the midbrain intact in vitro, which has allowed us to perform whole-cell recordings from identified gaze-controlling cells in the optic tectum, while delivering natural and focal light stimuli within the visual field and monitoring and manipulating the synaptic responses. The retinotopic map in the lamprey tectum and the aligned motor map have been described in considerable detail (22,26), and the lamprey nervous system from forebrain to spinal cord is experimentally very accessible, well described, and also conserved throughout vertebrate evolution (30-32).Although most mammalian studies have focused on the role of the retinotopic excitatory circuits that mediate signal transmission between the superficial layer and the deeper layers (33-36), only more recent studies have emphasized the role of GABAergic circuits in the collicular control of gaze (37-45). The question how collicular GABAergic systems affect stimulus selection for gaze motor action has, however, remained unanswered because most studies have relied on extracellular recordings in vivo and therefore have not allowed an analysis of the synaptic basis for these inhibitory interactions.…”

“…Afferents from retina provide a direct input to the superficial layers of the optic tectum, where a retinotopic map is formed (23-26). The intermediate and deep layers give rise to projections to brainstem areas and a motor map is formed that is responsible for the coordination of eye, head, and body movements (22,(27)(28)(29).…”

“…To achieve this, we have developed a preparation in lamprey that maintains the eye and the midbrain intact in vitro, which has allowed us to perform whole-cell recordings from identified gaze-controlling cells in the optic tectum, while delivering natural and focal light stimuli within the visual field and monitoring and manipulating the synaptic responses. The retinotopic map in the lamprey tectum and the aligned motor map have been described in considerable detail (22,26), and the lamprey nervous system from forebrain to spinal cord is experimentally very accessible, well described, and also conserved throughout vertebrate evolution (30-32).…”