My expertise is in vivo retinal imaging in animals using adaptive optics. My current role in the Department of Ophthalmology is to translate the novel retinal imaging technologies developed in the Dubra lab to the bench by developing close interdisciplinary cooperation between optical engineers, biologists and clinicians. I spent 3 years at the University of Rochester using adaptive optics to study vision restoration in mouse models of blindness. Formally trained as a neuroscientist, I have a passion for engineering. I love making and inventing. I am self taught in electronics, CAD design and 3d printing. I love to invent solutions to old problems, and refining existing inefficient processes.

Honors & Awards

  • Dean's Honors List Award, Faculty of Science, The University of Melbourne (2007)
  • Department of Optometry and Vision Sciences Honors Scholarship, The University of Melbourne (2007)
  • Department of Optometry and Vision Sciences Summer Research Scholarship, The University of Melbourne (2007)
  • Australian Postgraduate Award PhD Scholarship, Australian Government (2008)
  • The University of Sydney Postgraduate Research Support Scheme, The University of Sydney (2010)
  • Dean's Prize for Student Research Publications for best paper published by a graduate student, Sydney Medical School, The University of Sydney (2012)
  • Paxinos-Watson Prize - most significant neuroscience paper published in 2011 by a full member, Australasian Neuroscience Society (2013)
  • Young Investigator Award Honorable Mention, The Optical Society Fall Vision Meeting (2014)
  • Travel Fellowship, XVIIth International Symposium on Retinal Degeneration (2016)
  • Young Investigator Aware for best presentation, The Optical Society Fall Vision Meeting (2016)

Boards, Advisory Committees, Professional Organizations

  • Member, Australasian Neuroscience Society (2008 - 2012)
  • Member, Association for Research in Vision and Ophthalmology (2014 - Present)
  • Member, Society for Neruoscience (2016 - Present)

Professional Education

  • Bachelor of Science, University Of Melbourne (2007)
  • Doctor of Philosophy, University Of Sydney (2012)

Research & Scholarship

Current Research and Scholarly Interests

We combine advanced imaging technology with cutting edge developments in engineered fluorescent biosensors to study the function of neurons and other cell types in the living eye. The purpose is to study the health and function of the retina in the living animal with greater resolution than ever before, to understand the mechanisms of retinal diseases, and to develop new therapies for treating blindness.


  • Functional imaging of neurons in the living eye, Stanford University (April 1, 2017)

    Using adaptive optics to image the retina of living animals, we aim to study the changes to neuronal health in diseases such as photoreceptor degeneration and trauma to the optic nerve.


    Stanford, CA, USA


All Publications

  • Relationship between cortical state and spiking activity in the lateral geniculate nucleus of marmosets. The Journal of physiology Pietersen, A. N., Cheong, S. K., Munn, B., Gong, P., Martin, P. R., Solomon, S. G. 2017


    How parallel are the primate visual pathways? In the present study, we demonstrate that parallel visual pathways in the dorsal lateral geniculate nucleus (LGN) show distinct patterns of interaction with rhythmic activity in the primary visual cortex (V1). In the V1 of anaesthetized marmosets, the EEG frequency spectrum undergoes transient changes that are characterized by fluctuations in delta-band EEG power. We show that, on multisecond timescales, spiking activity in an evolutionary primitive (koniocellular) LGN pathway is specifically linked to these slow EEG spectrum changes. By contrast, on subsecond (delta frequency) timescales, cortical oscillations can entrain spiking activity throughout the entire LGN. Our results are consistent with the hypothesis that, in waking animals, the koniocellular pathway selectively participates in brain circuits controlling vigilance and attention.The major afferent cortical pathway in the visual system passes through the dorsal lateral geniculate nucleus (LGN), where nerve signals originating in the eye can first interact with brain circuits regulating visual processing, vigilance and attention. In the present study, we investigated how ongoing and visually driven activity in magnocellular (M), parvocellular (P) and koniocellular (K) layers of the LGN are related to cortical state. We recorded extracellular spiking activity in the LGN simultaneously with local field potentials (LFP) in primary visual cortex, in sufentanil-anaesthetized marmoset monkeys. We found that asynchronous cortical states (marked by low power in delta-band LFPs) are linked to high spike rates in K cells (but not P cells or M cells), on multisecond timescales. Cortical asynchrony precedes the increases in K cell spike rates by 1-3 s, implying causality. At subsecond timescales, the spiking activity in many cells of all (M, P and K) classes is phase-locked to delta waves in the cortical LFP, and more cells are phase-locked during synchronous cortical states than during asynchronous cortical states. The switch from low-to-high spike rates in K cells does not degrade their visual signalling capacity. By contrast, during asynchronous cortical states, the fidelity of visual signals transmitted by K cells is improved, probably because K cell responses become less rectified. Overall, the data show that slow fluctuations in cortical state are selectively linked to K pathway spiking activity, whereas delta-frequency cortical oscillations entrain spiking activity throughout the entire LGN, in anaesthetized marmosets.

    View details for DOI 10.1113/JP273569

    View details for PubMedID 28116750

  • Binocular Visual Responses in the Primate Lateral Geniculate Nucleus. Current biology : CB Zeater, N., Cheong, S. K., Solomon, S. G., Dreher, B., Martin, P. R. 2015


    The dorsal lateral geniculate nucleus (dLGN) in carnivores and primates is a laminated structure, where each layer gets visual input from only one eye [1, 2]. By contrast, in rodents such as mice and rats, the dLGN is not overtly laminated, the retinal terminals from the two eyes are only partially segregated [3, 4], and many cells in the binocular segment of dLGN get excitatory inputs from both eyes [5, 6]. Here, we show that the evolutionary ancient koniocellular (K) division of primate dLGN, like rodent dLGN, forms a subcortical site of binocular integration. We recorded single-cell activity in dLGN of anesthetized marmoset monkeys. As expected, cells in the parvocellular (P) and magnocellular (M) layers received monocular excitatory inputs. By contrast, many cells in the K layers received excitatory inputs from both eyes. The specialized properties of distinct K sub-populations (for example, blue-yellow color selectivity) were preserved across the two eye inputs, and where tested, the contrast sensitivity of each eye input was roughly matched. The results argue that evolutionarily widely separated orders such as rodents and primates have a shared strategy of integrating signals from the two eyes in subcortical circuits.

    View details for DOI 10.1016/j.cub.2015.10.033

    View details for PubMedID 26778654

  • Temporal response properties of koniocellular (blue-on and blue-off) cells in marmoset lateral geniculate nucleus JOURNAL OF NEUROPHYSIOLOGY Pietersen, A. N., Cheong, S. K., Solomon, S. G., Tailby, C., Martin, P. R. 2014; 112 (6): 1421-1438


    Visual perception requires integrating signals arriving at different times from parallel visual streams. For example, signals carried on the phasic-magnocellular (MC) pathway reach the cerebral cortex pathways some tens of milliseconds before signals traveling on the tonic-parvocellular (PC) pathway. Visual latencies of cells in the koniocellular (KC) pathway have not been specifically studied in simian primates. Here we compared MC and PC cells to "blue-on" (BON) and "blue-off" (BOF) KC cells; these cells carry visual signals originating in short-wavelength-sensitive (S) cones. We made extracellular recordings in the lateral geniculate nucleus (LGN) of anesthetized marmosets. We found that BON visual latencies are 10-20 ms longer than those of PC or MC cells. A small number of recorded BOF cells (n = 7) had latencies 10-20 ms longer than those of BON cells. Within all cell groups, latencies of foveal receptive fields (<10° eccentricity) were longer (by 3-8 ms) than latencies of peripheral receptive fields (>10°). Latencies of yellow-off inputs to BON cells lagged the blue-on inputs by up to 30 ms, but no differences in visual latency were seen on comparing marmosets expressing dichromatic ("red-green color-blind") or trichromatic color vision phenotype. We conclude that S-cone signals leaving the LGN on KC pathways are delayed with respect to signals traveling on PC and MC pathways. Cortical circuits serving color vision must therefore integrate across delays in (red-green) chromatic signals carried by PC cells and (blue-yellow) signals carried by KC cells.

    View details for DOI 10.1152/jn.00077.2014

    View details for Web of Science ID 000341694700017

    View details for PubMedID 24920024

  • Antidromic latency of magnocellular, parvocellular, and koniocellular (Blue-ON) geniculocortical relay cells in marmosets. Visual neuroscience Cheong, S. K., Johannes Pietersen, A. N. 2014; 31 (3): 263-273


    We studied the functional connectivity of cells in the lateral geniculate nucleus (LGN) with the primary visual cortex (V1) in anesthetized marmosets (Callithrix jacchus). The LGN sends signals to V1 along parallel visual pathways called parvocellular (P), magnocellular (M), and koniocellular (K). To better understand how these pathways provide inputs to V1, we antidromically activated relay cells in the LGN by electrically stimulating V1 and measuring the conduction latencies of P (n = 7), M (n = 14), and the "Blue-ON" (n = 5) subgroup of K cells (K-BON cells). We found that the antidromic latencies of K-BON cells were similar to those of P cells. We also measured the response latencies to high contrast visual stimuli for a subset of cells. We found the LGN cells that have the shortest latency of response to visual stimulation also have the shortest antidromic latencies. We conclude that Blue color signals are transmitted directly to V1 from the LGN by K-BON cells.

    View details for DOI 10.1017/S0952523814000066

    View details for PubMedID 24703370

  • Cortical-Like Receptive Fields in the Lateral Geniculate Nucleus of Marmoset Monkeys JOURNAL OF NEUROSCIENCE Cheong, S. K., Tailby, C., Solomon, S. G., Martin, P. R. 2013; 33 (16): 6864-6876


    Most neurons in primary visual cortex (V1) exhibit high selectivity for the orientation of visual stimuli. In contrast, neurons in the main thalamic input to V1, the lateral geniculate nucleus (LGN), are considered to be only weakly orientation selective. Here we characterize a sparse population of cells in marmoset LGN that show orientation and spatial frequency selectivity as great as that of cells in V1. The recording position in LGN and histological reconstruction of these cells shows that they are part of the koniocellular (K) pathways. Accordingly we have named them K-o ("koniocellular-orientation") cells. Most K-o cells prefer vertically oriented gratings; their contrast sensitivity and TF tuning are similar to those of parvocellular cells, and they receive negligible functional input from short wavelength-sensitive ("blue") cone photoreceptors. Four K-o cells tested displayed binocular responses. Our results provide further evidence that in primates as in nonprimate mammals the cortical input streams include a diversity of visual representations. The presence of K-o cells increases functional homologies between K pathways in primates and "sluggish/W" pathways in nonprimate visual systems.

    View details for DOI 10.1523/JNEUROSCI.5208-12.2013

    View details for Web of Science ID 000317723000018

    View details for PubMedID 23595745

  • Colour and pattern selectivity of receptive fields in superior colliculus of marmoset monkeys JOURNAL OF PHYSIOLOGY-LONDON Tailby, C., Cheong, S. K., Pietersen, A. N., Solomon, S. G., Martin, P. R. 2012; 590 (16): 4061-4077


    The main subcortical visual targets of retinal output neurones (ganglion cells) are the parvocellular and magnocellular layers of the dorsal lateral geniculate nucleus (LGN) in the thalamus. In addition, a small and heterogeneous collection of ganglion cell axons projects to the koniocellular layers of the LGN, to the superior colliculus (SC), and to other subcortical targets. The functional (receptive field) properties and target specificity of these non-parvocellular, non-magnocellular populations remain poorly understood. It is known that one population of koniocellular layer cells in the LGN (blue-On cells) receives dominant functional input from short-wavelength sensitive (S or ‘blue') cones. Here we asked whether SC neurones also receive S cone inputs. We made extracellular recordings from single neurones (n = 38) in the SC of anaesthetised marmoset monkeys. Responses to drifting and flashed gratings providing defined levels of cone contrast were measured. The SC receptive fields we recorded were often binocular, showed ‘complex cell' like responses (On–Off responses), strong bandpass spatial frequency tuning, direction selectivity, and many showed strong and rapid habituation to repeatedly presented stimuli. We found no evidence for dominant S cone input to any SC neurone recorded. These data suggest that S cone signals may reach cortical pathways for colour vision exclusively through the koniocellular division of the lateral geniculate nucleus.

    View details for DOI 10.1113/jphysiol.2012.230409

    View details for Web of Science ID 000308128100032

    View details for PubMedID 22687612

  • The impact of brief exposure to high contrast on the contrast response of neurons in primate lateral geniculate nucleus JOURNAL OF NEUROPHYSIOLOGY Camp, A. J., Cheong, S. K., Tailby, C., Solomon, S. G. 2011; 106 (3): 1310-1321


    Prolonged exposure to an effective stimulus generally reduces the sensitivity of neurons early in the visual pathway. Yet eye and head movements bring about frequent changes in the retinal image, and it is less clear that exposure to brief presentations will produce similar desensitization. To address this, we made extracellular recordings from single neurons in the lateral geniculate nucleus of anesthetized marmosets, a New World primate. We measured the contrast response for drifting gratings before and after 0.5-s exposure to a high-contrast drifting grating, a stationary grating, or a blank screen. Prior exposure to the drifting grating reduced the contrast sensitivity of cells in the magnocellular pathway, on average by 23%; this reduction remained strong when the adapting and test stimuli were separated by 0.4 s. Exposure to a stationary grating of the preferred spatial phase did not change the contrast response; exposure to the opposite spatial phase did. None of the brief adaptors reduced the sensitivity of parvocellular cells. We conclude that brief periods of high contrast, such as those that would be expected to occur during a normal visual fixation, are sufficient to reduce the sensitivity of magnocellular-pathway cells.

    View details for DOI 10.1152/jn.00943.2010

    View details for Web of Science ID 000294775500020

    View details for PubMedID 21653705

  • Slow intrinsic rhythm in the koniocellular visual pathway PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Cheong, S. K., Tailby, C., Martin, P. R., Levitt, J. B., Solomon, S. G. 2011; 108 (35): 14659-14663


    Slow rhythmic changes in nerve-cell activity are characteristic of unconscious brain states and also may contribute to waking brain function by coordinating activity between cortical and subcortical structures. Here we show that slow rhythms are exhibited by the koniocellular (K) pathway, one of three visual pathways beginning in the eye and projecting through the lateral geniculate visual relay nucleus to the cerebral cortex. We recorded activity in pairs and ensembles of neurons in the lateral geniculate nucleus of anesthetized marmoset monkeys. We found slow rhythms are common in K cells but are rare in parvocellular and magnocellular cell pairs. The time course of slow K rhythms corresponds to subbeta (<10 Hz) EEG frequencies, and high spike rates in K cells are associated with low power in the theta and delta EEG bands. By contrast, spontaneous activity in the parvocellular and magnocellular pathways is neither synchronized nor strongly linked to EEG state. These observations suggest that parallel visual pathways not only carry different kinds of visual signals but also contribute differentially to brain circuits at the first synapse in the thalamus. Differential contribution of sensory streams to rhythmic brain circuits also raises the possibility that sensory stimuli can be tailored to modify brain rhythms.

    View details for DOI 10.1073/pnas.1108004108

    View details for Web of Science ID 000294425900059

    View details for PubMedID 21844334

  • Linear and Nonlinear Contributions to the Visual Sensitivity of Neurons in Primate Lateral Geniculate Nucleus JOURNAL OF NEUROPHYSIOLOGY Solomon, S. G., Tailby, C., Cheong, S. K., Camp, A. J. 2010; 104 (4): 1884-1898


    Several parallel pathways convey retinal signals to the visual cortex of primates. The signals of the parvocellular (P) and magnocellular (M) pathways are well characterized; the properties of other rarely encountered cell types are distinctive in many ways, but it is not clear that they can provide signals with the same fidelity. Here we study this by characterizing the temporal receptive field of neurons in the lateral geniculate nucleus of anesthetized marmosets. For each neuron, we measured the response to a flickering uniform field, and, from this, estimated the linear and nonlinear receptive fields using spike-triggered average (STA) and spike-triggered covariance (STC) analyses. As expected the response of most P-cells was dominated by the STA, but the response of most M-cells required additional nonlinear components, and these usually acted to suppress cell responses. The STC analysis showed stronger suppressive axes in suppressed-by-contrast cells, and both suppressive and excitatory axes in on-off cells. Together, the STA and the STC analyses form a model of the temporal response to a large uniform field: under this model, the information that was provided by suppressed-by-contrast cells or on-off cells approached that provided by the P- and M-cells. However, whereas P- and M-cells provided more information about luminance, the nonlinear cells provided more information about the contrast energy. This suggests that the nonlinear cells provide complimentary signals to those of P- and M-cells, with reasonably high fidelity, and may play an important role in normal visual processing.

    View details for DOI 10.1152/jn.01118.2009

    View details for Web of Science ID 000282649900007

    View details for PubMedID 20685925