Visual direction-selective neurons in the pretectum of the rainbow trout.
M.Klar & K.-P. Hoffmann
Brain Research Bulletin, 57:431-433, 2002
- In mammals, the essential neuronal substrate for the generation of the
horizontal optokinetic nystagmus (hOKN) are the nucleus of optical tract (NOT) and the dorsal terminal nucleus
(DTN). The medial terminal nucleus (MTN) is thought to be involved in vertical OKN control. Characteristic for
all of these neurons is a high-direction selectivity. Although behavioural hOKN experiments in different fish species
show comparability to mammals, little is known about the neuronal OKN control in fish. In preceding studies, we
demonstrated that the rainbow trout has a nearly symmetrical monocular hOKN at low stimulus speeds. With increasing
visual stimulus speeds (>14 degrees /s), the monocular hOKN becomes asymmetrical with a temporo to nasal preferred
direction. For visual stimulation, we presented random-dot-patterns projected by a planetarium inside a perimeter.
We tested four rotation axes of the planetarium, yaw (0 degrees -180 degrees ), roll (90 degrees -270 degrees ),
diagonal (45 degrees -225 degrees ) and anti-diagonal (135 degrees -315 degrees ). In every position, the visual
stimulus turned in clockwise and counter-clockwise direction. In a subregion of the pretectum of nine fish, we
recorded 47 direction-selective neurons. Analysis of tuning-curves and preferred direction vectors show that these
neurons encode both horizontal (yaw) and vertical (roll) visual stimulus directions. These results suggest that
the control of horizontal and vertical OKN might not segregate into different nuclei in fish.
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