Salk Institute for Biological Studies


John H. Reynolds

John H. Reynolds

Systems Neurobiology Laboratory



The long-range goal of our laboratory is to understand the neural mechanisms of selective visual attention at the level of the individual neuron and the cortical circuit, and to relate these to perception and conscious awareness. We take as our starting point the observation that the brain is limited in the amount of visual information it can process at any moment in time. For instance, when people are asked to identify the objects in a briefly presented scene, they become less accurate as the number of objects increases. This inability to process more than a few objects at a time reflects the limited capacity of some stage (or stages) of sensory processing, decision-making, or behavioral control. Somewhere between stimulating the retina and generating a behavioral response, objects compete with one another to pass through this computational bottleneck. We seek to understand this selection process using a combination of visual psychophysics, neurophysiology, and computational neural modeling.

"The long-range goal of our laboratory is twofold–to understand the fundamental nature of the computations that are carried out by the neocortex and to understand how and why these computations fail in brain disease."

Evolution has endowed our brains with a system of neural mechanisms whose function is to choose which information will be selected to guide our behavioral decisions. When this system fails, as in disorders such as schizophrenia, Alzheimer's disease and attention deficit hyperactivity disorder (ADHD), the effects on the quality of life can be devastating. Reynolds's team is working to decipher the neural mechanisms of attention, which are key to understanding and treating brain diseases in which the attention system fails.

At any point in time, our brains are able to process only a small fraction of the totality of information available in the sensory environment. Even if we wanted to pay attention to many things at once, there are limits on how many stimuli we can juggle simultaneously. What's more, only a small fraction of available sensory information is needed to make effective behavioral decisions, and the information that is needed changes from moment to moment, depending on our needs and the risks and possibilities presented by our ever-changing environment. The attentional system thus plays the critical role of "perceptual gatekeeper," selecting task relevant information for processing while keeping distracting information from entering conscious awareness.

Reynolds's team has found that when attention is directed toward a stimulus, attentional control centers of the brain send signals that tell the perceptual systems to favor certain circuits over others. As a result, neurons that convey information about an attended stimulus are more active, while neurons that would otherwise convey distracting information are suppressed. They have also recently discovered that attention reduces the variability or "noise" in neuronal signals, improving the quality of information about the visual stimuli to which we attend.

They are now conducting experiments to understand the neural mechanisms underlying these attention-dependent changes in neural signaling. To do this, they use a range of techniques, including neurophysiology, neuroanatomy, computational modeling, visual psychophysics and cutting-edge optogenetic techniques that enable the use of viruses to change the DNA of neurons so that they create proteins that act as light sensors. This enables them to use light to alter the activity of specific types of neurons and understand their role in perception, attention and behavior.

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