Figure 7.

Optogenetic activations of Po terminal axons focused on M1wk layer 3 or on S1BF layer 1 modify subsequent tactile stimulus processing in other cortical layers. (A) Diagram of the M1wk experimental protocol. Mechanical stimuli (air puffs) were applied to the trimmed contralateral whiskers (three trains of 100 stimuli, 1 Hz). A single long-lasting pulse of blue-light (473 nm, 300 ms, <30 mW/mm²) was applied through a fiber optic whose tip was positioned in L3M1wk, pointing inwards to illuminate Po axons terminals expressing ChR2 + eYFP in this layer. The light pulse was applied immediately after the first train (“control”) of whisker stimuli. SEPs and unit responses were recorded separately in the superficial and deep layers (shaded in different color hues, respectively). (B) L3 Po terminal axons activation modified SEP1 in others M1wk cortical layers. Changes in SEP1 area immediately after light application (gray) and during the recovery train (white) are represented as the variation of percentage to the control values at different depths. Negative values symbolize inhibition and positive values facilitation. Representative traces examples of SEPs recorded during control (black line) and after light application (gray dashed line) trains are shown below. (C) Blue-light activation of Po terminal axons in L3 of M1wk modulates unit responses and more superficially located layers. Mean values of changes in unit responses are represented as the variation of spike counts percentage to the control train. (D) Diagram of the S1BF experimental protocol. A single long-lasting pulse of light was applied through a fiber optic whose tip was placed in L1 S1BF, pointing inwards. Others conventions as in panel (A). (E) Light-activation of thalamocortical Po axons in L1 changes subsequent SEP1 recorded in others cortical layers. Conventions as in panel (B). (F) Light activation of Po terminal axons in L1 S1BF modify unit responses in both superficial and deep layers. Conventions as in panel (C).