In vivo Large-Scale Cortical Mapping Using Channelrhodopsin-2 Stimulation in Transgenic Mice Reveals Asymmetric and Reciprocal Relationships between Cortical Areas

Abstract

We have mapped intracortical activity in vivo independent of sensory input using arbitrary point channelrhodopsin-2 (ChR2) stimulation and regional voltage sensitive dye imaging in B6.Cg-Tg (Thy1-COP4/EYFP)18Gfng/J transgenic mice. Photostimulation of subsets of deep layer pyramidal neurons within forelimb, barrel, or visual primary sensory cortex led to downstream cortical maps that were dependent on synaptic transmission and were similar to peripheral sensory stimulation. ChR2-evoked maps confirmed homotopic connections between hemispheres and intracortical sensory and motor cortex connections. This ability of optogentically activated subpopulations of neurons to drive appropriate downstream maps suggests that mechanisms exist to allow prototypical cortical maps to self-assemble from the stimulation of neuronal subsets. Using this principle of map self-assembly, we employed ChR2 point stimulation to map connections between cortical areas that are not selectively activated by peripheral sensory stimulation or behavior. Representing the functional cortical regions as network nodes, we identified asymmetrical connection weights in individual nodes and identified the parietal association area as a network hub. Furthermore, we found that the strength of reciprocal intracortical connections between primary and secondary sensory areas are unequal, with connections from primary to secondary sensory areas being stronger than the reciprocal.

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…Similarly, we repeated these experiments using antagonists of glutamatergic transmission, DNQX (500 mM) and AP5 (200 mM). Relatively high drug concentrations were required because of surface application and are consistent with blockade that we have achieved in the past 40 . Attempts to generate seed pixel correlation maps from residual spontaneous infraslow activity following treatment with TTX or DNQX and AP5 resulted in the absence of any functional structure even when presented as filled contour plots to guide visual analysis (Fig.…”

“…1b) giving us confidence that our VSD signal was reflecting truly infraslow activity. Using a giant, bilateral, cranial window experimental preparation 33,40,41 , we showed that infraslow spontaneous cortical activity exhibits bilaterally synchronous, regionally discrete areas of activation ( Fig. 2a and Supplementary Movie 1).…”

“…Although we did observe an increase in background correlation in infraslow spontaneous activity versus slow spontaneous activity, global signal removal was not necessary using VSD imaging to reveal infraslow functional connectivity. The dye also has an excellent signal-to-noise ratio and its efficacy has been established in monitoring sensory-evoked, optogenetically evoked and spontaneous activity at high spatial and temporal resolution 27,28,31,33,40,51 . We have previously demonstrated the high spatial resolution of our VSD imaging with an optical resolution of 67 mm (ref.…”

“…The resolution along the optical axis of our imaging setup was B1 mm (ref. 40). VSD fluorescence was filtered using a 673-703-nm bandpass optical filter (Semrock, New York, NY).…”

Optogenetic neuronal stimulation promotes functional recovery after stroke

“…Optogenetic approaches have been used in rodents to probe neuronal circuits for several neurological/neurodegenerative diseases, including Parkinson disease (30) and epilepsy (31). Recent studies have also used optogenetics to map functional organization after stroke (32)(33)(34)(35). The safety and efficacy of using optogenetics in nonhuman primates has also been characterized (29,36).…”