Journal of Neuroscience, Vol 15, 5139-5151, Copyright © 1995 by Society for Neuroscience
Characterization of a forebrain gaze field in the archistriatum of the barn owl: microstimulation and anatomical connections
EI Knudsen, YE Cohen and T Masino
Department of Neurobiology, Stanford University School of Medicine, California 94305-5401, USA.
We present evidence that the archistriatum in the forebrain of the barn owl
participates in gaze control, that it can mediate gaze changes
independently of the optic tectum (OT), and that it projects in parallel to
both the OT and to saccade-generating circuitry in the brainstem tegmentum.
These properties are similar to those of the frontal eye fields (FEF) in
the prefrontal cortex of primates. The forebrain was surveyed for sites
where electrical microstimulation would induce head saccades. Head (and
eye) saccades were elicited from the anterior 70% of the archistriatum, a
region that we refer to as the archistriatal gaze fields (AGF). At single
stimulation sites in the AGF, saccade amplitude tended to vary as a
function of stimulation parameters (current strength, pulse frequency, and
train duration) and starting head position. In contrast, saccade direction
was largely independent of these parameters. Saccade direction did vary
over a wide range of primarily contraversive directions with the site of
stimulation in the AGF. Using anatomical pathway tracing techniques, we
found that the archistriatum projects strongly and in parallel to the deep
layers of the OT and to nuclei in the midline brainstem tegmentum. Previous
work has shown that electrical microstimulation of either of these
brainstem regions evokes saccadic movements of the head and/or eyes (du Lac
and Knudsen, 1990; Masino and Knudsen, 1992b). Inactivation of the OT with
lidocaine reduced the size but did not eliminate (or change the direction
of) the saccades evoked by AGF stimulation. The direct anatomical pathway
from the archistriatum to the midline tegmental nuclei can account for
saccades that persist following OT inactivation. The similarities between
the AGF in barn owls and the FEF in primates suggest that the same general
plan of anatomical and functional organization supports the contribution of
the forebrain to gaze control in a wide variety of species.
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