Abstract
In the mammalian primary visual cortex (V1), lateral spreading of excitatory potentials is believed to be involved in spatial integrative functions, but the underlying cortical mechanism is not well understood. Visually-evoked population-level responses have been shown to propagate beyond the V1 initial activation site in mouse, similar to higher mammals. Visually-evoked responses are, however, affected by neuronal circuits prior to V1 (retina, LGN), making the separate analysis of V1 difficult. Intracortical stimulation eliminates these initial processing steps. We used in vivo RH1691 voltage-sensitive dye (VSD) imaging and intracortical microstimulation in adult C57BL/6 mice to elucidate the spatiotemporal properties of population-level signal spreading in V1 cortical circuits. The evoked response was qualitatively similar to that measured in single-cell electrophysiological experiments in rodents: a fast transient fluorescence peak followed by a fast and a slow decrease or hyperpolarization, similar to EPSP and fast and slow IPSPs in single cells. The early cortical response expanded at speeds commensurate with long horizontal projections (at 5% of the peak maximum, 0.08–0.15 m/s) however, the bulk of the VSD signal propagated slowly (at half-peak maximum, 0.05–0.08 m/s) suggesting an important role of regenerative multisynaptic transmission through short horizontal connections in V1 spatial integrative functions. We also found a tendency for a widespread and fast cortical response suppression in V1, which was eliminated by GABAA-antagonists gabazine and bicuculline methiodide. Our results help understand the neuronal circuitry involved in lateral spreading in V1.
Highlights
In the primary visual cortex (V1), many neurons can be activated by visual stimuli applied outside the boundaries of their classical receptive field (RF) [1, 2]
We verified that the assumed V1 stimulation site was within V1 and that the most prominent secondary activity focus was outside of V1 in V2L, by relating voltage-sensitive dye (VSD) responses around stimulation sites in the assumed V1 and V2L areas to marked locations on cytochrome oxidase C (COC) tangential slices in one animal
The VSD signal of cortical activity evoked by stimulation was recorded at each site, and the site was marked by the application of 50 μA current for 3–4 seconds
Summary
In the primary visual cortex (V1), many neurons can be activated by visual stimuli applied outside the boundaries of their classical receptive field (RF) [1, 2]. Elucidating the spatiotemporal properties of the horizontal propagation of excitatory signals, either sub- or super-threshold, is important to understand the function of V1 in visual perception, since it might play a crucial role in visual processing, such as in improving the specificity and reliability of visual responses [10], in formation of dynamic activity patterns relevant to illusions [5, 9, 11, 12]. This, has its drawbacks when one tries to investigate how V1 neuronal circuitry shapes the spatiotemporal properties of cortical activity, since the visually evoked cortical responses are strongly affected by the state of visual circuits prior to V1, i.e. retina and LGN
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call