Chronobiology & Visual Neuroscience

The brain combines signals across the eyes. This process is well-characterized for the perceptual anatomical pathway through V1 that primarily codes contrast, where interocular normalization ensures that responses are approximately equal for monocular and binocular stimulation. But we have much less understanding of how luminance is combined binocularly, both in the cortex and in subcortical structures that govern pupil diameter. Here I will describe the results of experiments using a novel combined EEG and pupillometry paradigm to simultaneously index binocular combination of luminance flicker in parallel pathways. The results show evidence of a more linear process than for spatial contrast, that may reflect different operational constraints in distinct anatomical pathways.

The rising and setting of the sun is accompanied by changes in both the irradiance and the spectral distribution of the sky. Since the discovery of intrinsically photosensitive retinal ganglion cells (ipRGCs) 20 years ago, considerable progress has been made in understanding melanopsin's contributions to encoding irradiance. Much less is known about the cone inputs to ipRGCs and how they could encode changes in the color of the sky. I will summarize our recent connectomic investigation into the cone-opponent inputs to primate ipRGCs and the implications of this work on our understanding of circadian photoentrainment and the evolution of color vision.

Beyond vision, light triggers a variety of non-image forming responses. Amongst these is the pupillary light reflex, commonly used by ophthalmologists to gauge the function of the optic nerve head. In my talk, I will share some of our latest work on optimizing the use of the pupillary light reflex to detect functional loss in ocular diseases in clinics.

Do all components of the living human eye have a measurable diurnal rhythm? In this talk I will discuss methodologies and results of studies on adolescents and young adults. I will also touch upon the associations between diurnal rhythms of the eye and behavioral activities.

Night shift work is associated with adverse health effects and leads to misalignment between timing cues from the environment and the endogenous circadian clock. In this presentation, I will discuss the effect of circadian misalignment induced by night shift work on peripheral 24-h rhythms on the transcriptome and metabolome in humans, presenting findings from both controlled laboratory studies and field studies. Furthermore, I will highlight the importance of taking into account interindividual differences in the response to circadian misalignment.

This talk will (1) describe patterns and correlates of objectively assessed motor activity (2) present findings on the inter-relationships among motor activity, sleep and circadian rhythms and mood disorders; (3) describe potential of cross species studies of motor activity and related systems to inform human chronobiology research

The retina is probably the most accessible part of the vertebrate central nervous system. Its computational logic can be interrogated in a dish, from patterns of lights as the natural input, to spike trains on the optic nerve as the natural output. Consequently, retinal circuits include some of the best understood computational networks in neuroscience. The retina is also ancient, and central to the emergence of neurally complex life on our planet. Alongside new locomotor strategies, the parallel evolution of image forming vision in vertebrate and invertebrate lineages is thought to have driven speciation during the Cambrian. This early investment in sophisticated vision is evident in the fossil record and from comparing the retina’s structural make up in extant species. Animals as diverse as eagles and lampreys share the same retinal make up of five classes of neurons, arranged into three nuclear layers flanking two synaptic layers. Some retina neuron types can be linked across the entire vertebrate tree of life. And yet, the functions that homologous neurons serve in different species, and the circuits that they innervate to do so, are often distinct to acknowledge the vast differences in species-specific visuo-behavioural demands. In the lab, we aim to leverage the vertebrate retina as a discovery platform for understanding the evolution of computation in the nervous system. Working on zebrafish alongside birds, frogs and sharks, we ask: How do synapses, neurons and networks enable ‘function’, and how can they rearrange to meet new sensory and behavioural demands on evolutionary timescales?

Since the discovery of the intrinsically photosensitive retinal ganglion cells (ipRGCs) – just two decades ago – substantial work has been carried out trying to understand their functioning. In this seminar, I’ll focus on pupillometry studies that have provided key clues about ipRGC behavior. Specifically, the interaction between the intrinsic response, rods, and cones will be discussed.

Retinal light exposure is modulated by our behavior, and light exposure patterns show strong variations within and between persons. Yet, most laboratory studies investigated influences of constant lighting settings on human daytime functioning and sleep. In this presentation, I will discuss a series of studies investigating light-induced moderations in sleepiness, vitality and sleep, with a strong focus on the temporal dynamics in these effects, and the bi-directional relation between persons' light profiles and their behavior.

Laboratory studies have shown that meaningful changes in light exposure lead to phase shifts in melatonin rhythm. In natural settings, however, light is a very complex signal. How melatonin responds to weekly- and seasonal-dependent variations in light exposure is still poorly understood. In this talk I will present results from a series of observational and intervention studies on the relationship between melatonin and light exposure in the field.

Profound changes in the visual environment occur over the course of the day-night cycle. There is therefore a profound pressure for cells and circuits within the visual system to adjust their function over time, to match the prevailing visual environment. Here, I will discuss electrophysiological data collected from nocturnal and diurnal rodents that reveal how the visual code is ‘temporally optimised’ by 1) the retina’s circadian clock, and 2) a change in behavioural temporal niche.

What happens to human sleep and circadian rhythms in space? There are many challenges that affect sleep in space, including unusual patterns of light exposure and the influence of microgravity. This talk will review the causes and consequences of sleep loss and circadian misalignment during spaceflight and will discuss how missions to the Moon and Mars will be different than missions to the International Space Station.