Binocular response modulation in the lateral geniculate nucleus

Abstract

The dorsal lateral geniculate nucleus of the thalamus (LGN) receives the main outputs of both eyes and relays those signals to the visual cortex. Each retina projects to separate layers of the LGN so that each LGN neuron is innervated by a single eye. In line with this anatomical separation, visual responses of almost all of LGN neurons are driven by one eye only. Nonetheless, many LGN neurons are sensitive to what is shown to the other eye as their visual responses differ when both eyes are stimulated compared to when the driving eye is stimulated in isolation. This, predominantly suppressive, binocular modulation of LGN responses might suggest that the LGN is the first location in the primary visual pathway where the outputs from the two eyes interact. Indeed, the LGN features several anatomical structures that would allow for LGN neurons responding to one eye to modulate neurons that respond to the other eye. However, it is also possible that binocular response modulation in the LGN arises indirectly as the LGN also receives input from binocular visual structures. Here we review the extant literature on the effects of binocular stimulation on LGN spiking responses, highlighting findings from cats and primates, and evaluate the neural circuits that might mediate binocular response modulation in the LGN.

Binocular Modulation of Monocular V1 Neurons

“…Moreover, cat LGN features anatomical connections between monocular layers that are either absent or less prominent in primates [32][33][34]. Accordingly, responses of the vast majority of cat LGN cells modulate under binocular stimulation, whereas only a small minority of LGN neurons in the macaque seem to be sensitive to both eyes (see [35] for more extensive discussion). Our results suggest that despite these species differences, monocular neurons in primary visual cortex of both cats and monkeys exhibit binocular modulation.…”

“…Specifically, monocular LGN neurons might modulate under binocular stimulation and imprint this response pattern onto their projection targets in L4 of V1. Indeed, binocular modulation occurs in cat LGN (see [35] for review). It is unclear whether this binocular modulation results from feedback from V1 [32,[41][42][43].…”

Adaptation of Intracortical Signaling Concurs with Enhanced Encoding Efficiency

“…The two retinae receive no feedback from its projection targets in the primary visual pathway (Ortiz et al 2017). And at the next step of visual processing, in the lateral geniculate nucleus (LGN), almost all neurons respond to one eye only (Zeater et al 2015; Dougherty et al 2018). Hence, sensory signals from the two eyes remain largely segregated before they arrive in V1.…”

Binocular modulation of monocular V1 neurons

“…Moreover, cat LGN features anatomical connections between monocular layers that are either absent or less prominent in primates (Hayhow, 1958, Laties and Sprague, 1966, Guillery and Colonnier, 1970, Sanderson et al, 1971, Saini et al, 1981. Accordingly, responses of the vast majority of cat LGN cells modulate under binocular stimulation, whereas only a small minority of LGN neurons in the macaque seem to be sensitive to both eyes (see Dougherty et al, 2018 for a more extensive discussion of species differences). Our results suggest that despite these species differences, monocular neurons in primary visual cortex of both cats and monkeys exhibit binocular modulation.…”

“…Specifically, LGN monocular neurons might modulate under binocular stimulation and imprint this response pattern onto their projection targets in layer 4C of V1. Indeed, binocular modulation has been reported in cat LGN (see Dougherty et al, 2018 for review). Moreover, cortical inactivation studies aimed at delineating whether this binocular modulation is caused by feedback from V1 produced equivocal results (Singer, 1970, Sanderson et al, 1971, Schmielau and Singer, 1977, Pape and Eysel, 1986, Varela and Singer, 1987.…”