Purchase this article with an account.
L. Tychsen, D. Sarezky, J. Leonard, P. Foeller; Effects of Callosotomy on Nasotemporal Smooth Pursuit in Macaque Monkey: Validating a Cerebral Gaze Asymmetry Mechanism. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2874.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Knowledge to date regarding horizontal gaze control in primates indicates that smooth eye tracking is driven by neurons in the medial-superior-temporal (MST) area of each cerebral hemisphere. The directional organization is ipsiversive: MST of the right hemisphere drives rightward tracking and MST of the left hemisphere, leftward tracking. Visual motion neurons of areas V1/MT must send feed forward projections--representing rightward vs. leftward motion from each visual hemi field--to the appropriate MST, presumably through the splenium (posterior quarter) of the corpus callosum. Convolving visual hemi fields on rightward vs. leftward motion, callosotomy would be expected to disrupt tracking of stimuli moving away from the vertical meridian within each hemi field (centrifugal motion), but spare tracking of stimuli moving toward the vertical meridian (centripetal motion). To test this prediction, we performed a partial callosotomy.
The splenium (i.e. posterior portion) of the callosum was sectioned in a 1 yr old monkey. The rostrum, genu and body of the callosum were left intact. Several weeks later, horizontal step-ramp motion stimuli were confined to the right or left visual hemi fields to elicit centripetal vs. centrifugal smooth pursuit when viewing with either eye monocularly.
Smooth eye velocity evoked by ramps of stimulus motion revealed decrements in gain of ~ 20% for centrifugal motion within each hemi field. The response to centripetal motion was unaffected. Latencies for centrifugal motion were prolonged (~20%) when compared to those for centripetal motion. Saccadic latency and accuracy was unaffected.
Sectioning of the callosal splenium produced the predicted asymmetry of pursuit, but the effect was underwhelming. Two interpretations are possible: 1) the sectioning may have been less complete than assumed, or 2) visual projections from areas V1/MT travel through more anterior regions of the callosum (e.g. the body as well as the splenium). Further experiments will be necessary to establish the validity of these interpretations.
This PDF is available to Subscribers Only