Journal of Neuroscience, Vol 6, 723-733, Copyright © 1986 by Society for Neuroscience
Movements resembling orientation or avoidance elicited by electrical stimulation of the superior colliculus in rats
N Sahibzada, P Dean and P Redgrave
Some studies have reported that stimulation of the superior colliculus in
rats produces orienting responses, as it does in a number of species.
However, other studies have reported movements resembling avoidance and
escape, which are not characteristic of collicular stimulation in other
mammals. This apparent discrepancy was investigated by systematically
recording the effects on head and body movements of electrical stimulation
at a large number of sites throughout the superior colliculus (SC) and
surrounding structures. It was found that the nature of the movements
observed depended on the location of the stimulating electrode.
Contralateral head and body movements resembling orienting and approach
were obtained from sites in the intermediate and deep layers in rostral
colliculus, the intermediate white layer and immediately surrounding tissue
in central colliculus, and in all layers except deep white in caudal
colliculus. At the remaining responsive sites, movements resembling
avoidance and escape were obtained. The most common response was an
ipsilateral cringelike movement of the body that developed into ipsilateral
locomotion, followed by running and jumping as the current was increased.
These movements were obtained from sites in the superficial and
intermediate layers rostrally; from the intermediate gray and the medial
superficial and deep layers in central colliculus; and from the deep layers
and underlying tegmentum caudally. The distributions of sites, together
with evidence from other studies, suggested the following conclusions:
Within the superficial layers, avoidance responses were obtained from a
region of the superior colliculus that appeared to represent the upper
visual field, whereas orienting responses were obtained from a region
apparently representing the lower visual field. Stimulation of the area
containing the cells of origin of the predorsal bundle produced orientation
and approach movements, whereas the avoidance and escape movements were
probably mediated by parts of the ipsilateral descending pathway. The
stimulation-induced avoidance and escape may reflect the importance of such
responses to visual "events," particularly in the upper part of the visual
field, in animals, like rats, with many predators.
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