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1. Visual abilities decline during normal aging, and many of these declines are due to neural changes in the retina or central visual pathways. We have begun studies of the primate visual system to investigate the location and nature of these changes as well as to answer general questions about the effects of aging on neural function. We began with the dorsal lateral geniculate nucleus (LGN) because it is the main structure through which visual information passes on the way to cortex and because the parallel parvocellular and magnocellular pathways, which may be affected differently by aging, are anatomically distinct there. 2. Single -cell recordings were made in the LGN of young adult (5–16 yr) and old (25–28 yr) rhesus monkeys. We made quantitative measures of a wide variety of response properties for a large number of parvocellular (n = 257) and magnocellular (n = 113) neurons in the two groups of animals. As a result, in addition to studying the effects of aging, we were able to make quantitative comparisons between parvocellular and magnocellular neurons using larger samples than have been studied previously and for some properties that have not been studied before. 3. We found that magnocellular neurons have significantly higher maximal response rates and signal -to -noise ratios than parvocellular neurons. However, response latencies to visual stimulation were similar for neurons in the two types of layers. In agreement with previous studies, magnocellular neurons had higher maximal contrast sensitivity and higher contrast gain than parvocellular neurons. However, the sensitivity difference occurred because nearly all of the neurons with low sensitivities (< 10) were in the parvocellular layers, not because neurons in the magnocellular layers had the highest sensitivities. 4. Neurons with the smallest receptive-field centers, the highest spatial-frequency resolutions, and the highest optimal spatial frequencies were found in the parvocellular layers. However, the overall distributions of each of these properties overlapped substantially for neurons in the two types of layers, and the mean values were not significantly different. The mean high temporal-frequency cutoff was significantly higher for magnocellular than parvocellular neurons, but the difference was small (only 3 Hz), and it occurred because many parvocellular neurons had lower cutoffs than any seen in the magnocellular layers, not because magnocellular neurons had the highest temporal-frequency cutoffs. Parvocellular neurons also had narrower temporal-frequency tuning than magnocellular neurons. However, there was no significant difference in optimal temporal frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

The relationships of photosynthetic characteristics to the competitive interactions of a C plant, Chenopodium album, and a C plant, Amaranthis retroflexus, were investigated in different temperature and water supply regimes. Both species had similar photosynthetic rates at 25°C, but at higher temperatures, Amaranthus had substantially greater rates than Chenopodium. Conversely, at lower temperatures, Chenopodium had an advantage. The competitive abilities in mixtures exhibited a close parallel to the photosynthetic performances with Amaranthus having an advantage at high temperatures and Chenopodium an advantage at low temperatures. These competitive outcomes were determined primarily by differences in relative growth rates prior to canopy closure. In the respective, temperature regimes, the species having the highest photosynthetic rate, which resulted an more rapid growth, overtopped and shaded the other species at the time of canopy closure. These results demonstrate that differences in photosynthetic temperature response between C and C plants can be an important determinant in competitive interactions, but at least in this case, the influence is primarily through, events prior to the actual initiation of competition.In contrast to temperature, growth of the plants under limited water supply had no influence on the competitive interactions. Thus, the presence of the C pathway alone was not sufficient to yield a competitive advantage over the C species under water limited conditions.

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The 3-item RCS exhibits good sensitivity and specificity for the detection of MCI and dementia, and higher cognitive function on the RCS is protective against nursing home placement and mortality. The RCS may be a useful screening instrument for the detection of cognitive dysfunction in the primary care setting.

In the July 2016 issue of this journal, Dr. Mary Tinetti proposed that geriatric medicine abandon attempts to increase the numbers of board‐certified geriatricians and change focus to the development of a “small elite workforce.” What would be gained and what sacrificed by accepting this challenge? We agree that the best clinical use of a scarce resource, specialty trained geriatricians, is to care for frail, complex, severely ill elderly adults and to help design and study novel interventions in research, education, and care models to improve the care of all older adults, but for this to happen, all other providers must attain specific competency in the care of older adults. This article responds and discusses alternative pathways for teaching geriatrics care, training specialists, and geriatrics fellows.

1. X, Y, and W cells in the A and C layers of the cat's dorsal lateral geniculate nucleus (LGN) were tested for responses to stimulation of the nondominant eye. The main purpose was to determine the incidence of nondominant-eye excitation and inhibition among different classes of cells and to examine the spatial-frequency tuning of responses to the nondominant eye. 2. Of 198 cells that were tested with drifting sine-wave gratings presented to the nondominant eye, 109 (55%) showed statistically significant responses. Four types of responses were observed: an increase in the mean discharge rate (F0 excitation), a decrease in the mean discharge rate (F0 inhibition), an increased modulation at the fundamental frequency of the grating (F1 excitation), and a decreased modulation at the fundamental frequency of the grating (F1 inhibition). Overall, 29% of the cells responded with inhibition, 24% responded with excitation, and 2% showed both excitation and inhibition, depending upon the spatial frequency and/or the harmonic response component. The relative incidence of excitation and inhibition was similar for X, Y, and W cells, for cells with on-center and off-center receptive fields, for cells with different receptive-field eccentricities, and for cells in each LGN layer. In addition, within layers A and A1, responses were similar for cells at different distances from the laminar borders. 3. Spatial-frequency response functions indicated that cells could have band-pass or low-pass spatial-frequency tuning through the nondominant eye. Band-pass cells tended to be narrowly tuned (less than or equal to 1 octave), and low-pass cells responded to a broader range of spatial frequencies. These properties were similar for X, Y, and W cells. Spatial resolution tended to be low (less than or equal to 0.8 c/deg for most cells), although a few cells responded to the highest spatial frequency tested (5.4 c/deg). Likewise, optimal spatial frequency was low (less than or equal to 0.2 c/deg) for most cells. These properties were similar for X and Y cells, and there was a weak tendency for X and Y cells to have higher optimal spatial frequencies and spatial resolutions than W cells. 4. In terms of absolute change in activity, responses to drifting gratings were weak. However, cells that were inhibited generally showed 20-60% decreases in activity to the optimal spatial frequency, and cells that were excited generally showed 40-100% increases. Response amplitudes were similar for X, Y, and W cells.(ABSTRACT TRUNCATED AT 400 WORDS)