background preloader

The Brain in Discover magazine

Facebook Twitter

The Man With Uncrossed Eyes : Neuroskeptic. “GB” is a 28 year old man with a curious condition: his optic nerves are in the wrong place. Most people have an optic chiasm, a crossroads where half of the signals from each eye cross over the midline, in such a way that each half of the brain gets information from one side of space. GB, however, was born with achiasma – the absence of this crossover.

It’s an extremely rare disorder in humans, although it’s more common in some breeds of animals, such as Belgian sheepdogs. Here’s GB and a normal brain for comparison: Canadian neurologists Davies-Thompson and colleagues describe GB in a new paper using functional neuroimaging to work out how his brain is organized. In the absence of a left-right crossover, all of the signals from GB’s left eye end up in his left visual cortex, and vice versa.

It turns out that the two halves of space overlap in GB’s visual cortex, as these fMRI results show: This is a fascinating case report, and vision neuroscientists will find much to ponder here. Napping Neurons Explain Sleep-Deprived Blunders | Memory, Emotions, & Decisions. When tiredness sets in, poor decisions and clumsiness often follow. In a study published last April, scientists may have pinpointed the biological basis of such mistakes: tiny clusters of neurons that start napping, even as the brain stays awake. To explore the phenomenon, neuroscientist Giulio Tononi of the University of Wisconsin at Madison tempted lab rats to stay awake longer than usual by supplying them with a steady stream of new toys. At the same time, he measured their brain activity through electroencephalography (EEG).

With so much exploring to do, the rats seemed alert, but measurements told a different story. Though EEG recordings indicated overall wakefulness, small groups of neurons briefly went offline. Our Strange, Important, Subconscious Light Detectors. Studies like Foster’s prompted a number of researchers to look for those missing cells. The first clue came in 2000, when neuroscientist Ignacio Provencio, now at the University of Virginia, found a light- capturing pigment called melanopsin in the ganglion layer of the retina. It was a bizarre discovery, since the ganglion layer was thought only to relay electric signals from the rods and cones, not catch its own light. But in 2002, Samer Hattar of Johns Hopkins University and David Berson of Brown University identified individual retinal ganglion cells containing melanopsin. They further demonstrated that the cells—called intrinsically photosensitive retinal ganglion cells, or ipRGCs—could detect light.

Like the rods and cones, ipRGCs are most sensitive to a particular color: blue, in this case. And like other retinal ganglion cells in the eye, the ipRGCs grow long fibers that snake out to join the optic nerve. Another surprise: Not all ipRGCs are the same. The Brain: The Troublesome Bloom of Autism | Mental Health. Eric Courchesne managed to find a positive thing about getting polio: It gave him a clear idea of what he would do when he grew up. Courchesne was stricken in 1953, when he was 4. The infection left his legs so wasted that he couldn’t stand or walk. “My mother had to carry me everywhere,” he says. His parents helped him learn how to move his toes again. Courchesne was 11 when the braces finally came off, and his parents patiently helped him practice walking on his own.

When Courchesne wasn’t competing at gymnastics, he was studying neuroscience. At the time, Courchesne was investigating how children’s brains respond to new pieces of information. Autism had cut the boy off from the social world, Courchesne realized. In the three decades since, autism has gone from obscurity to painful familiarity. As they develop, autistic brains bloom with an overabundance of neurons, Courchesne finds. Scientists had done a few anatomical studies on the autistic brain, but the results were ambiguous. Science's Long—and Successful—Search for Where Memory Lives | Memory, Emotions, & Decisions. During that visit, the three sat down to see if they could figure out the discrepancy in the data. The “problem,” Silva felt, might in fact be an opportunity: a hint of how they could use CREB as a tool not merely to enhance or suppress memories but to explore each new memory’s precise location—to locate the engram.

Maybe after all these years, it would be possible to find true tracks of memory in the brain. Perhaps it was actually necessary for only a small percentage of neurons to be involved in forming a memory. Maybe memory formation is a kind of competitive sport. By the time Josselyn’s study was published, in 2001, she had already accepted an invitation extended to her and her husband, Paul Frankland, also a postdoc in neuroscience, to join Silva at UCLA. Once there, Josselyn dreamed up an ingeniously elaborate study with Silva to test their “neuronal competition” theory of memory formation.

But this is where things got seriously strange. Josselyn happens to like Tom Cruise. The Brain: The Connections May Be the Key | Mind & Brain. There was just one problem: Nobody knew what the connectome looked like. MRI scans can capture the entire brain, but they can get down to a resolution of only a few cubic millimeters, not nearly fine enough. Other methods, such as staining, allow scientists to look at one neuron at a time but not to track the broader links between them. Seung needed a way to see every neuron in a given piece of brain tissue.

He found the way by teaming up with scientists who know how to slice brains very, very thinly. Each image is a few hundredths of an inch across, but it’s packed with neural cross sections. Such images contain details far beyond what had ever been seen before. If memories really are encoded in cell assemblies the way Hebb claimed, Seung should be able to observe those assemblies (pdf). The collaboration between humans and computers has sped the process along. It would be simple enough, he suggests, for neurosurgeons to set aside a smidgen of tissue removed during human surgery. The "Interpreter" in Your Head Spins Stories to Make Sense of the World | Mind & Brain. The left hemisphere specializes in speech, language, and intelligent behavior, and a split-brain patient’s left hemisphere and language center has no access to sensory information if it is fed only to the right brain. In the case of vision, the optic nerves leading from each eye meet inside the brain at what is called the optic chiasm.

Here, each nerve splits in half; the medial half (the inside track) of each crosses the optic chiasm into the opposite side of the brain, and the lateral half (that on the outside) stays on the same side. The parts of both eyes that attend to the right visual field send information to the left hemisphere and information from the left visual field goes to and is processed by the right hemisphere. More than a few years into our experiments, we were working with a group of split-brain patients on the East Coast. We wondered what they would do if we sneaked information into their right hemisphere and told the left hand to do something [pdf].

The Brain Is Ready for Its Close-Up | Biotechnology.