Binocular Modulation of Monocular V1 Neurons

Neurophysiology: Charting the Confluence of the Two Eyes’ Information Streams

“…Using their more modern technique, Dougherty et al [2] confirmed what has been known: most neurons within layer 4, but not those in other layers of V1, can be driven only by stimuli shown to their dominant eye: they are monocular neurons. While this observation corroborated the long-standing idea of the eyes' signals being kept separate in layer 4, their next observation did not: most layer-4 neurons, although monocular by the above definition, did show a statistically different response when both eyes were stimulated simultaneously, as compared to when the dominant eye was stimulated alone (Figure 2).…”

“…Interestingly, they found that the more common, suppressive, type of modulation actually occurs later in layer 4 than it does elsewhere in V1, even though layer 4, being V1's input layer, receives visual input first. Dougherty et al [2] reasonably interpret this as tentative evidence that this suppressive modulation involves a neural circuit in which the eyes' signals first meet outside of layer 4, and in which the result of this interaction is then fed back to the monocular cells of layer 4 (the less common, facilitatory, kind of modulation did not bear this signature).…”

“…The logical conclusion relayed in textbooks since that time is that binocular integration, as it is called, happens within V1 but downstream of its input layer, termed layer 4. A new study by Dougherty et al [2], reported recently in Current Biology, offers a correction to this view, and provides new clues as to the neural circuit responsible for binocular integration. Dougherty et al [2] measured neural responses in V1 of awake behaving macaque monkeys that viewed stimuli on a screen.…”

“…A new study by Dougherty et al [2], reported recently in Current Biology, offers a correction to this view, and provides new clues as to the neural circuit responsible for binocular integration. Dougherty et al [2] measured neural responses in V1 of awake behaving macaque monkeys that viewed stimuli on a screen. Whereas many existing studies have recorded such responses using electrodes that have a single contact point, one notable feature of this new study is the use of linear multielectrode arrays.…”

“…Beyond this demonstration that the two eyes' signals do interact in V1's input layer, Dougherty et al [2] also performed several additional analyses to shed light on the nature of this interaction. One analysis with a particularly striking outcome rests on the fact that modulation by the non-dominant eye was observed in monocular neurons throughout V1, not just in layer 4.…”