General anesthesia can be tolerated by patients older than 65

Contrary to conventional medical wisdom, a new study by NYU Langone Medical Center researchers shows that healthy elderly patients with severe to profound hearing loss can undergo a surgical procedure to receive cochlear implants with minimal risk. "Due to concerns about the effects of general anesthesia, many elderly people with hearing loss are not receiving the implants which can significantly improve their hearing and quality of life," according to Anil Lalwani, M.D., Mendik Foundation Professor of Otolaryngology and Chairman of the Department of Otolaryngology at NYU School of Medicine and a study co-author. "The elderly are often incorrectly considered too fragile for this life transforming technology that can deliver them from a world of silence and loneliness to a world of hearing and engagement," says Dr. Lalwani. The new study is published in the February issue of the journal The Laryngoscope.

The National Institute on Aging estimates that about one-third of Americans between ages 65 and 74 have hearing difficulty – and that number increases to 50 percent in people 85 and older. In about 10% of the elderly, the impairment is so severe that conventional hearing aids provide little benefit. The inability to communicate interferes greatly with daily living and can lead to cognitive impairment, personality changes, depression, reduced functional status and social isolation.

The researchers conducted a retrospective chart review of 70 patients over 70 years of age who received cochlear implants under general anesthesia at NYU Langone Medical Center between 1984 and 2007. The patients were divided into risk groups and intraoperative and postoperative anesthesia-related complications were identified. Most patients tolerated the procedure and there was no long-term morbidity or mortality related to the surgery or anesthesia.

The researchers concluded that general anesthesia is well tolerated by elderly patients undergoing cochlear implantation. Any pre - existing medical condition is a better predictor of intraoperative and postoperative complication than age alone, they observed. Jung T. Kim, M.D. Vice chairman of the Department of Anesthesiology at NYU School of Medicine and a study co-author said "As seniors embrace a healthy and active lifestyle, it is important that age alone should not deter a person from having surgery that could potentially improve their quality of life."

Arrangement of receptors appears uniformly random across individuals and species

Despite the striking aromatic differences between coffee, peppermint, and pine, a new mapping of the nose's neural circuitry suggests a haphazard patchwork where the receptors for such disparate scents are as likely as not to be neighbors. Inexplicably, this seemingly random arrangement is faithfully preserved across individuals and even species, with cells that process the same scent located in precisely the same location on the olfactory bulb, the brain's first processing station for odors. The crazy-quilt map of odor-processing neurons on the front lines of the olfactory system is described by Harvard University neuroscientists in the February issue of the journal Nature Neuroscience.

"It had been thought that the layout of the olfactory bulb was variable from individual to individual, but followed a chemotopic order where cells handling similar odor responses are near each other," says Markus Meister, the Jeff C. Tarr Professor of Molecular and Cellular Biology in Harvard's Faculty of Arts and Sciences. "Here we show that the layout is actually very precise -- the same from animal to animal -- but doesn't appear to follow any chemotopic order whatsoever."

Working with mice and rats, Meister and colleague Venkatesh N. Murthy recorded neural responses to several hundred distinct odors, including anise, beer, cloves, coffee, ginger, lemon, orange, peppermint, pine, rose, and even fox pheromones. The neuroscientists found that across individuals and even across the two species, bundles of neurons from a given type of odor receptor -- known as glomeruli -- were found in almost exactly the same spot on the olfactory bulb, a sensory structure measuring some four to five millimeters across and located at the very front of the brain.

"Glomeruli from different receptors line the surface of the olfactory bulb like an array of close-packed marbles," says Murthy, professor of molecular and cellular biology at Harvard. "Across individuals the location of a given glomerulus varies by only one array position. Compared to the size of the map, this represents a remarkable developmental precision of one part in 1,000." Meister and Murthy then analyzed whether nearby glomeruli detect similar odors, such as those with similar chemical structures. Neuroscientists have previously hypothesized axes of similarities along which odors might be classified. "One might expect that nearby glomeruli should have similar odor sensitivities," Meister says, "but we were surprised to find this was not the case. The odor response spectra of two neighboring glomeruli were as dissimilar as those of distant glomeruli."

This seemingly haphazard layout of sensory properties stands in marked contrast to other brain maps, such as those governing vision, touch, and hearing. In these three cases, our brains represent the outside world using ordered maps -- such as when neighboring points in visual space activate neighboring points on the retina. "That sort of arrangement makes sense, since most brain computation is local, relying on short connections between nearby cells," Murthy says. "This is necessary because the connections between neurons occupy most of the volume available to the brain, and long-distance connections require more of this volume."

Meister and Murthy suspect that the deliberate randomness in rodents' odor maps is likely also found in humans, which have only one-third as many receptors but are capable, in some extreme cases, of discerning tens of thousands of distinct smells.

Meister and Murthy's co-authors on the Nature Neuroscience paper are Edward R. Soucy, Dinu F. Albeanu, and Antoniu L. Fantana, all of Harvard's Department of Molecular and Cellular Biology and Center for Brain Science. Their work was funded by Harvard University.