One very unique feature of us primates is that we have foveated eyes. The primate retinas consist of densely packed photoreceptors at the foveal region but relatively loose in the periphery. In order to obtain the best vision with our eyes, we constantly move them to put the things we want to see onto our fovea. Such eye movements are usually ballistic, called saccades. In order to make a successful saccade requires multiple steps including making decision of the saccade target, preparing for the proper saccade and suppressing unwanted saccade, and also shift of attention to the saccade target. Because of the complex and dedicated nature of saccadic eye movements, it has been shown for decades that the cortical and subcortical brain areas controlling saccadic eye movements are also involved in cognitive function, such as attention and decision making. Several cortical areas, like frontal eye field (FEF) and lateral intraparietal area (LIP), and the subcortical area, superior colliculus (SC) had been shown to contribute to saccadic eye movement. However, whether each brain area serve specific function in specific time point in saccade generation or this is a joint work from multiple brain areas simultaneously is still not clear.
I have been investigating saccadic eye movements and the consequence of such movement altering our attention and visual perception during my Ph.D. research. I have found that there was correlation between the preparatory neuronal signal for saccades in the SC and the alternation of attention. I would like to further investigate the interaction in the saccade network using advanced calcium imaging and electrophysiological methods to simultaneously record multiple cortical and subcortical brain areas involving in saccade generation. To tease apart the role of each brain region, I would use the stat-of-the-art optogenetics tools to excite or inhibit these areas in various time point during saccade preparation and execution. To explain the above idea in more detail, I will train one small new world monkey, the marmosets, for saccadic tasks, such as gap task, delayed saccade, and memory-guided saccade task (Fig 1). After the marmosets are successfully trained, I will monitor the activity of neurons by performing simultaneous calcium signal recording in the brain areas involved in saccade generation while they are engaged in the saccade tasks (Fig 2a, 2b). To visualize the change of calcium ions in behaving subjects, I will inject engineered Adeno-associated virus (AAV) and express calcium indicator in the neurons. With this approach, I expected to have a clear view of the potential involvement of each brain areas in different time points of the saccade tasks. Furthermore, I will use either optogenetic excitation or inhibition methods to test the causal involvement of those brain areas in saccade generation (Fig 2c). This will help me to resolve the causal relationship of cortical and subcortical interactions involved in saccade generation.
Chih-Yang Chen went to Germany and obtained his PhD in Neuroscience form the University of Tuebingen in 2017. He later moved to Kyoto and undertook postdoctoral training with JSPS Postdoctoral Fellowship in Prof. Tadashi Isa’s group in Kyoto University until 2020. He was than appointed as an Assistant Professor in 2020 in the Institute for the Advanced Study of Human Biology (ASHBi) of Kyoto University.
Chen, C. -Y., Hoffmann, K. P., Distler, C., & Hafed, Z. M. (2019). The Foveal Visual Representation of the Primate Superior Colliculus. Current Biology, Vol. 29, No. 13, pp. 2109-2119
Chen, C. -Y., Sonnenberg, L., Weller, S., Witschel, T., & Hafed, Z. M. (2018). Spatial frequency sensitivity in macaque midbrain. Nature Communications. doi: 10.1038/s41467-018-05302-5
Chen, C. -Y. and Hafed, Z. M. (2017). A neural locus for spatial-frequency specific saccadic suppression in visual-motor neurons of the primate superior colliculus. Journal of Neurophysiology, Vol. 117, No. 4, pp. 1657-1673
Hafed, Z. M. and Chen, C. -Y. (2016). Sharper, stronger, faster upper visual field representation in primate superior colliculus. Current Biology, Vol. 26, No. 13, pp. 1647-1658
Chen, C. -Y., Ignashchenkova, A., Thier, P., and Hafed, Z. M. (2015). Neuronal response gain enhancement prior to microsaccades. Current Biology, Vol. 25, No. 16, pp. 2065-2074.
Chen, C. -Y. and Hafed, Z. M. (2013). Postmicrosaccadic enhancement of slow eye movements. The Journal of Neuroscience, Vol. 33, No. 12, pp. 5375-5386.
Annual Attempto Prize (for Tübingen-based research published), the Attempto Foundation in Germany (2015);
Annual Trainee Professional Development Awards, Society of Neuroscience (2016);
The Excellent Research Award, ASHBi Retreat 2020 (2020)