Fig. 8.

Laminar profile of evoked responses for the entire stimulus sequence. A: single-unit spiking responses, organized by laminar compartment. Each row indicates the spiking responses of 1 unit across the entire trial (i.e., all 5 stimulus subsequent presentations), averaged across all trials. Periods of visual stimulation (STIM) are denoted by horizontal bars at bottom. All single-unit responses were normalized (norm.) for comparison (see materials and methods). B: mean current source density (CSD) across presentations. Stimulation is denoted by bars at top. C: difference in laminar spiking (ΔSpiking) between first (P₁) and fourth (P₄) stimulus presentations, averaged across sessions. D: difference in CSD sinks (ΔSiCSD) between P₁ and P₄, averaged across sessions. Interior of navy outline denotes P < 0.01; light blue outline, P < 0.05, and white outline, P < 0.1. Note that targeted feedback to inhibitory interneurons should result in a net increase of synaptic activity and thus an increase in CSD. The net decrease in current sinks shown suggests that the repetition-induced adaptation of synaptic drive in V1 might be supported by a different mechanism.