Controlling the Brain with Light

With a technique called optogenetics, researchers can probe how the nervous system works in unprecedented

Image: Photograph by Darren Braun

detail. Their findings could lead to better treatments for psychiatric problems.

Every day as a practicing psychiatrist, I confront my field’s limitations. Despite the noble efforts of clinicians and researchers, our limited insight into the roots of psychiatric disease hinders the search for cures and contributes to the stigmatization of this enormous problem, the leading cause worldwide of years lost to death or disability. Clearly, we need new answers in psychiatry. But as philosopher of science Karl Popper might have said, before we can find the answers, we need the power to ask new questions. In other words, we need new technology.

Developing appropriate techniques is difficult, however, because the mammalian brain is beyond compare in its complexity. It is an intricate system in which tens of billions of intertwined neurons—with multitudinous distinct characteristics and wiring patterns—exchange precisely timed, millisecond-scale electrical signals and a rich diversity of biochemical messengers.

Because of that complexity, neuroscientists lack a deep grasp of what the brain is really doing—of how specific activity patterns within specific brain cells ultimately give rise to thoughts, memories, sensations and feelings. By extension, we also do not know how the brain’s physical failures produce distinct psychiatric disorders such as depression or schizophrenia. The ruling paradigm of psychiatric disorders—casting them in terms of chemical imbalances and altered levels of neurotransmitters—does not do justice to the brain’s high-speed electrical neural circuitry. Psychiatric treatments are thus essentially serendipitous: helpful for many but rarely illuminating.

In Brief

• Neuroscientists have long been frustrated by their inability to study how the brain works in sufficiently precise detail. Unexpectedly, a solution has emerged from basic genetic research on micro­organisms that rely on light-responsive “opsin” proteins to survive.
• By inserting opsin genes into the cells of the brain, scientists can now use flashes of light to trigger firing by specific neurons on command. This technology, optogenetics, permits researchers to conduct extremely precise, cell type–targeted experiments in the brains of living, freely moving animals—which electrodes and other traditional methods do not allow.
• Although optogenetics is still in its infancy, it is already yielding potentially useful insights into the neuroscience underlying some psychiatric conditions.

Source: Scientific American magazine

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