Lecture: Structure and function of the “unconscious” visuo-motor system
Dr. Tadashi Isa, National Institute for Physiological Sciences, Okazaki, Japan:
'Structure and function of the “unconscious” visuo-motor system'
Visual inputs to the retina reaches the CNS via two major pathways, one is via the lateral geniculate nucleus and primary visual cortex (V1)(geniculo-striate pathway) and the other via the superficial layer of the superior colliculus (SC)(extrageniculate visual pathway). Despite abundant neuroanatomical knowledge on these two pathways, the role of individual pathways in guiding the goal-directed behavior has not been well characterized. It has been reported that some patients with lesion in V1 exhibit residual visuo-motor functions to localize the objects presented in the affected visual field under forced choice condition despite loss of awareness. Such residual visuo-motor capability has been called “blindsight” and ascribed to the function of the extrageniculate visual pathway. Therefore, the exrageniculate visual pathway has been supposed to be involved in the “unconscious” visuo-motor processing. However, the way how the visual inputs are converted to the action in the extrageniculate visual system is not well understood.
In this talk, I will first talk on the local circuits of the superior colliculus, a key node of the extrageniculate visual pathway, mostly by using the in-vitro slice preparation. The fundamental aspects of signal processing in the local circuits, especially, the intralaminar and interlaminar interactions, will be discussed.
Secondly, I will talk on our recent studies on the saccade control and cognitive functions of macaque monkeys with unilateral lesion of the primary visual cortex, an animal model of blindsight. In the present talk, I will focus on the (1) effects of reversible inactivation of SC on saccade control, (2) presence or absence of visual awareness and the neural correlates in the SC, (3) capability of working memory and its neural correlates in the SC, (4) whether thee animals can detect salient visual stimuli in the affected field under free-viewing condition. Based on these results, the capacity and limitation of the extrageniculate visual pathways in the control of saccades and cognitive functions will be discussed.
Isa T, Hall WC (2009) Exploring the superior colliculus in vitro. Journal of Neurophysiology (review), 102: 2581-2593.
Isa T, Yoshida M. (2009) Saccade control after V1 lesion revisited. Current Opinion in Neurobiology (review) 19: 608-614.
Takaura K, Yoshida M, Isa T (2011) Neural substrate of spatial memory in the superior colliculus after damage to the primary visual cortex. Journal of Neuroscience, in press.
- Werner Reichardt Centre for Integrative Neuroscience