Modification of oscillation strength by various FF input strengths.

(A) Cross-correlograms of cortical spikes. (i), (ii) In the OA network, the relative strength of gamma oscillation changes according to the FF input strength. The oscillation is strongest when FF input strength is 35∼40 µS/cm², and gradually diminishes as input strength increases. (iii) The E-I firing pattern shows that cortical oscillation is significantly modulated by the E-E interaction, and two different peaks coexist (‘spike doublets’, * and **). For a stronger FF input (50 µS/cm²), the E-I firing pattern shows only the normal gamma phase feature (***). Cortical oscillation is almost disappears for very strong FF input (80 µS/cm²). (B) The responsiveness difference between the OA network and the FF network changes from positive (for weak FF inputsthresh) to negative (for moderate FF inputs>S_thresh), and becomes zero (for strong FF inputs). Its absolute value (or cortical response modulation) is almost proportional to the strength of the gamma oscillation at each input strength (except at the FF response threshold, ∼30 µS/cm², where the difference changes from positive to negative). Also the difference in response delay between the OA network and the FF network is proportional to the strength of the gamma oscillation, which is controlled by the FF input strength.