Light and Behavior
The effect of light on behavior is both profound and multifaceted, with two major distinctions: form-vision and irradiance-measurement.
Detection of light at discrete points in space and time by an array of photoreceptor cells provides a spatial representation of the environment, termed form-vision. Form vision includes detection of shape, color, depth and motion.
Distinct from form-vision, detection of gross changes in light levels adapt an animal’s physiology and behavior to changes in the environment associated with altered light-conditions, termed irradiance-measurement. Irradiance-responses include daily and seasonal rhythms, and acute modulation of activity, sleep, and widely acting hormones like melatonin and cortisol.
In mice and humans, detection of light in the retina of the eye supports form-vision, regulates biological rhythms, and drives changes in behavioral states like sleepiness.
In practice, the influences of irradiance-measurement and form-vision compliment each other. The Bushy-tailed Wood rat feeds in mountainside woodland but nests on adjacent scree slopes, presumably because the rocks provide a safe haven from predators. This means that commuting between work and home is a risky business.
- Foraging during the day has an increased risk of predation and the body clock promotes activity at night and rest during the day. This body clock time is set by irradiance measurement detection of dawn and dusk.
- Crossing the rocks under bright moonlight also invites predation. The Wood rat can measure how bright it is outside, and stay safely near its nest on bright nights. This suppression of activity is driven by irradiance measurement.
- Crossing the rocks on very dark nights also presents a fall hazard and the Wood rat stays near its nest. In this case the limitations of spatial vision probably determine the behavior - if you can't see, you stay put.
In the lab, in a two-chamber light-dark preference test, aversion to light originates with irradiance-measurement that motivates the mouse to find cover or darkness, whereas form-vision may assist the mouse in identifying or finding the opening between the light-chamber and the dark-chamber.
Effects of retinal disease and traumatic injury to the retina
Because of this dual role, inherited disease or traumatic injury in the retina can cause:
- Devastating loss of vision.
- Abnormal responses to light that disrupt sleep and the body clock, depress mood, and unbalance important hormones.
Progress toward treating retinal disease is rapid, with recent success in gene replacement therapy, and hope for retinal prosthesis and stem cell replacement therapies. However, there is an immediate need to minimize the effect of disease on patients. Critically, we know very little about which eye diseases affect our physiology, how they affect us, and what we can do to minimize any negative effects.
Our goal is two-fold:
- Advance development of treatments for inherited retinal disease.
- Minimize the effect of untreated inherited retinal disease on health and performance.
Toward the first aim, we investigate how inherited eye diseases affect visual behavior in mice, and test the effectiveness of treatments in rescuing vision.
Toward the second aim, we are studying the effects of light on non-visual behaviors like sleep, and how those behaviors are disrupted by retinal disease or blast injury.