Figure 2: Thalamic spontaneous waves drive the communication between distinct thalamic nuclei.

(a) Fluorescence images of E16.5 Gbx2^CreER/+;R26^tdTomato 45 degrees thalamocortical acute slices loaded with the calcium indicator Cal520. Areas corresponding to the dLGN, VPM and MGv nuclei express tomato in function of the time of tamoxifen administration (upper panels). Maximum projection of Ca²⁺ waves (yellow) covering the three principal thalamic nuclei (lower panels). (b) Raster plot of the activity recorded in more than 250 individual cells in the dLGN-VPM during 10 min. The arrows label synchronous Ca²⁺ transients corresponding to Ca²⁺ waves. The lower panel shows examples of Ca²⁺ activity traces in four individual thalamic neurons (indicated by colour arrows in the raster plot) illustrating the three patterns of Ca²⁺ transients: asynchronous scattered, synchronous clusters and waves. (c) Cell-by-cell wave propagation. Upper panel: Percentage of neurons (over both dLGN and VPM nuclei) that are activated at every time point during wave propagation. Middle panel: Temporal spread of a wave front (colour coded). Lower panel: Examples of Ca²⁺ transients in four cells during a wave indicated in the middle panel (cell 1 initiated the wave). (d) Propagation of thalamic waves at E16.5 in acute slices: from the VPM into the dLGN (upper panels); from the dLGN into the VPM (middle panels); and from the VPM into the MGv nuclei (lower panels). The calcium signal intensity is coded in pseudocolour. Right panels for each wave show the temporal colour coded spread of the wave front from its origin (red zone) up to the borders of the nuclei. (e) Expression of GCaMP6-EGFP in embryonic acute thalamocortical slice from Gbx2^CreER/+;R26^{GCaMP6-EGFP/+} mice with tamoxifen administrated at E10.5. (f) Acute slice showing GCaMP6 in the thalamocortical projections at E16.5 (left). Maximum projection of a Ca²⁺ wave from the same slice (right, yellow) showing the propagation of the thalamic waves to the cortex. Traces showing the progression of a wave from VPM (1) to dLGN (2) that propagated along the TCAs (1′ and 2′) up to distinct medio-lateral cortical territories (3 and 4). (g) Temporal colour-coded spread of the wave shown in f. Scale bars, 200 μm in a, 100 μm in c and 200 μm in d–g.