Functional Maturation of the Macaque's Lateral Geniculate Nucleus

Abstract

Vision in infant primates is poor, but it is not known which structures in the eye or brain set the main limits to its development. We studied the visual response properties of 348 neurons recorded in the lateral geniculate nucleus (LGN) of macaque monkeys aged 1 week to adult. We measured spatial and temporal frequency tuning curves and contrast responses with drifting achromatic sinusoidal gratings. Even in animals as young as 1 week, the main visual response properties of neurons in the magnocellular (M) and parvocellular (P) divisions of the LGN were qualitatively normal, including the spatial organization of receptive fields and the characteristic response properties that differentiate M-and P-cells. At 1 and 4 weeks, spatial and temporal resolution were less than one-half of adult values, whereas contrast gain and peak response rates for optimal stimuli were about two-thirds of adult values. Adult levels were reached by 24 weeks. Analysis of correlations between S-potentials representing retinal inputs and LGN cells suggested that the LGN follows retinal input as faithfully in infants as in adults, implicating retinal development as the main driving force in LGN development. Comparisons with previously published psychophysical data and ideal observer models suggest that the relatively modest changes in LGN responses during maturation impose no significant limits on visual performance. In contrast to previous studies, we conclude that these limits are set by neural development in the visual cortex, not in or peripheral to the LGN.

Transmission of Spike Trains at the Retinogeniculate Synapse

“…Previous studies of connected retinal ganglion cells and LGN neurons have shown that mean firing rates are lower in LGN neurons (Kaplan et al, 1987;Movshon et al, 2005). In our population of 15 cells, the average probability of a retinal ganglion cell spike leading to an LGN spike was 46 Ϯ 16%.…”

“…With 98% of "priming" EPSPs falling within 33 ms of a spike, it appears that an instantaneous firing rate of 30 Hz is needed to bring an LGN neuron to threshold. The summation requirement explains the threshold portion of the function that relates the retinal spike rate to LGN spike rate (Lee et al, 1983;Movshon et al, 2005). This threshold nonlinearity is incorporated as the final stage of most neural models relating synaptic input to spike output (Dayan and Abbott, 2001).…”

The functional asymmetry of ON and OFF channels in the perception of contrast

“…1B). Fourier analyses determined that during recordings most (Ͼ90%) of the contrast stimuli used had a significant amount of energy (Ͼ50%) distributed in the low to medium spatial frequency range (Ͻ10 c/deg), which can effectively drive most LGN neurons under similar lighting conditions such as ours (Derrington and Lennie 1984;Movshon et al 2005). As an example, the contrast responses of a P ON neuron are shown in the form of raster plots (Fig.…”

Development of Temporal Response Properties and Contrast Sensitivity of V1 and V2 Neurons in Macaque Monkeys

“…Neurons in the LGN of infant monkeys have qualitatively adultlike spatial/temporal response properties as early as 1 wk of age, although retinal development limits the contrast sensitivity and the spatial/temporal resolving power of these neurons (Hawken et al 1997;Movshon et al 2005). However, "ideal observer analyses" indicated that immaturities in the retina or the LGN during the first several weeks of a monkey's life do not entirely account for the reduced spatial vision and therefore additional limits must be imposed by visual cortex Movshon et al 2005).…”

“…However, "ideal observer analyses" indicated that immaturities in the retina or the LGN during the first several weeks of a monkey's life do not entirely account for the reduced spatial vision and therefore additional limits must be imposed by visual cortex Movshon et al 2005).…”